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Lighting System - Diagnostic Information and Procedures Buick LaCrosse II

Exterior Lights ~44936 words

Diagnostic Instructions

  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Hazard Switch LED Backlighting ControlB096A 02B096A 01, B096A 041
Multifunction Switch 1 - Instrument Panel GroundB096A 01, B096A 04
1. Hazard Lamps Malfunction

Circuit/System Description

The instrument panel dimmer switch controls are located on the headlamp switch assembly and are used to increase and decrease the brightness of the interior backlighting components. When the instrument panel dimmer switch is placed in a desired brightness position, the body control module (BCM) receives a signal from the instrument panel dimmer switch and responds by applying a pulse width modulated (PWM) voltage to the hazard warning switch LED backlighting control circuit illuminating the LED to the desired level of brightness.

Conditions for Running the DTC

  1. Battery voltage must be between 9-16 V.
  2. Park lamps ON.

Conditions for Setting the DTC

DTC B096A 01

  1. The BCM detects an open/high resistance in the hazard warning switch LED backlighting control circuit.
  2. The BCM detects an open/high resistance in the hazard warning switch ground circuit.

DTC B096A 02

The BCM detects a short to ground in the hazard warning switch LED backlighting control circuit.

DTC B096A 04

  1. The BCM detects an open/high resistance in the hazard warning switch LED backlighting control circuit.
  2. The BCM detects an open/high resistance in the hazard warning switch ground circuit.

Actions Taken When the DTC Sets

The hazard warning switch LED backlighting will not illuminate.

Conditions for Clearing the DTC

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Reference Information

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S48C multifunction switch 1 - instrument panel. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 7 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Connect a test lamp between the control circuit terminal 5 and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the Hazard Lamps Switch Backlight ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the S48C multifunction switch 1 - instrument panel.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Instrument Panel Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Courtesy Lamps Control - Terminal 2 X7B1480 0211
Dome Lamps ControlB2615 0222
Center Compartment Lamp Switch Ground1
Dome/Reading Lamps - Front Ground1, 2
Dome/Reading Lamps - 2nd Row Ground1, 2
Instrument Panel Compartment Lamp Ground1
Sunshade Mirror Lamp - Left Ground1
Sunshade Mirror Lamp - Right Ground1
1. Courtesy Lamps Malfunction 2. Dome Lamps Malfunction

The body control module (BCM) supplies battery voltage to the front and rear reading lamps, left and right sunshade lamps, center console compartment lamp, and instrument panel compartment lamp via the courtesy lamp control circuit. When the instrument panel compartment or a sunshade mirror is opened, the switch contacts close allowing battery voltage to flow illuminating the respective lamps. The front and rear reading lamps are controlled by individual switches that are activated by the operator when additional cabin lighting is required. In the event that any of these courtesy lamps were to remain illuminated for more than 10 minutes with the ignition switch in the OFF position and no doors opened, the BCM will deactivate the courtesy lamp control circuit to prevent total battery discharge.

Battery voltage must be between 9-16 V.

The BCM detects a short to ground in the courtesy lamps control circuit.

The BCM will disable the circuit and all lamps controlled by the courtesy lamp control circuit will be inoperative.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connectors at the components listed below. E37F dome/reading lamps - front E37B dome/reading lamps - 2nd row E31L sunshade mirror lamp - left E31R sunshade mirror lamp - right E27 instrument panel compartment lamp S5 center console compartment lamp switch
  2. Connect a test lamp between the appropriate control circuit terminal listed below and ground. E37F dome/reading lamps - front terminal 1 E37B dome/reading lamps - rear terminal 1 E31L sunshade mirror lamp - left terminal A E31R sunshade mirror lamp - right terminal A E27 instrument panel compartment lamp terminal 1 S5 center console compartment lamp switch terminal 1
  3. Verify the test lamp turns ON and OFF when commanding the Inadvertent Load ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Test or replace the appropriate courtesy lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Sunshade Replacement»(/buick/lacrosse/ii-2009-2013/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling)
  2. «Instrument Panel Compartment Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Sunshade Illuminated Mirror Lamp Bulb Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Front Floor Console Armrest Compartment Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Dome and Reading Lamp Replacement - Front»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  6. «Dome and Reading Lamp Replacement - Rear»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  7. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Front Fog Lamp and Instrument Panel Dimmer Switch B+B257B 03, B1405 03B257B 03
Front Fog Lamp and Instrument Panel Dimmer Switch SignalB257B 03B257B 031
Front Fog Lamp Relay ControlB2530 02, B2530 04B2530 02, B2530 04B2530 01
Front Fog Lamp Control111
Front Fog Lamp Ground - Left1
Front Fog Lamp Ground - Right1
1. Front Fog Lamps Malfunction

The front fog lamp switch is an input to the body control module (BCM) and is contained in the headlamp switch assembly. The BCM supplies voltage to the front fog lamp switch via the front fog lamp and instrument panel dimmer switch B+ circuit. When the front fog lamp switch is pressed, voltage from the B+ circuit is pulled down through the front fog lamp switch resistor. The front fog lamp resistor is part of the resistor ladder that also provides the dimming signals for the instrument panel dimmer switches. The BCM receives the voltage signal through the front fog lamp and instrument panel dimmer switch signal circuit.

The front fog lamp relay is supplied with battery voltage at all times. The front fog lamp switch signal circuit is grounded momentarily by pressing the front fog lamp switch. The body control module (BCM) energizes the front fog lamp relay by applying ground to the front fog lamp relay control circuit. When the front fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the FRT FOG fuse to the front fog lamp control circuit which illuminates the front fog lamps.

  1. Battery voltage must be between 9-16 V.
  2. Front fog lamps ON.

DTC B2530 01

The BCM detects a short to voltage in the front fog lamp relay control circuit for 5 seconds or greater.

DTC B2530 02

The BCM detects a short to ground in the front fog lamp relay control circuit.

DTC B2530 04

The BCM detects an open in the front fog lamp relay control circuit.

DTC B2530 01 and B2530 04

The front fog lamps will not operate when the park lamps are ON and the front fog lamp switch is active.

DTC B2530 02

The front fog lamps always ON.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, disconnect the X2 harness connector at the X50A fuse block - underhood.
  2. Connect a test lamp between the control circuit terminal 19 and B+, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the control circuit terminal and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Test or replace the X50A fuse block - underhood.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Fuse Block Replacement»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F32UA Fuse B+B2545 01, B2545 04, B3950 01, B3950 04B2545 01, B2545 04, B3950 01, B3950 04
Backup Lamps ControlB2545 02B2545 04B2545 01
Backup Lamp Ground - Left1
Backup Lamp Ground - Right1
1. Backup Lamps Malfunction

With the engine running and the transmission in the reverse position, the transmission control module (TCM) sends a serial data message to the body control module (BCM). The message indicates that the gear selector is in the reverse position. The BCM applies battery voltage to the backup lamps control circuit illuminating the backup lamps. Once the driver moves the gear selector out of the reverse position, a message is sent by the TCM via serial data requesting the BCM to remove battery voltage from the backup lamps control circuit. The engine must be running for the backup lamps to operate.

  1. Battery voltage must be between 9-16 V.
  2. Engine RUNNING.
  3. Transmission placed in REVERSE gear.

DTC B2545 01

The BCM detects a short to voltage in the backup lamps control circuit.

DTC B2545 02

The BCM detects a short to ground in the backup lamps control circuit.

DTC B2545 04

The BCM detects an open/high resistance in the backup lamps control circuit.

DTC B2545 02 and B2545 04

The backup lamps will not operate.

DTC B2545 01

The backup lamps are always ON.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

  1. «Exterior Lights Schematics»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-wiring-schematic-diagrams)
  2. «Body Control System Schematics»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#data-communications-system)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 4 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X5 harness connector at the K9 body control module.
  4. Ignition OFF, exterior lamps OFF, trunk latch latched, remove the appropriate E5 backup lamp bulb at the appropriate E5 tail lamp assembly.
  5. Test for less than 5 ohms between the ground circuit terminal B and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  6. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  7. Verify the test lamp turns ON and OFF when commanding the Backup Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  8. Test or replace the appropriate E5 backup lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Backup Lamp Bulb Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Dome Lamp ControlB2615 0211
Dome Lamp Switch Cancel SignalB2555 02B2555 04B2555 01
Dome Lamp Switch ON SignalB2555 02B2555 04B2555 01
Dome/Reading Lamps - Front Ground1, 2
1. Dome Lamp Malfunction 2. Dome Lamp Switch Malfunction

The dome lamp switch has 3 positions: DOOR, OFF, and ON. The ON position provides a ground for continuous operation and the dome lamp will remain illuminated until the switch is placed in either the DOOR or OFF position. When in the DOOR position, the dome lamp operation is controlled by the body control module (BCM). When any door is opened, the door ajar switch contacts close and the BCM receives a door-open input. The BCM illuminates the dome lamp when any door is opened or a door lock/unlock request is activated with the key fob. After all doors have been closed, the dome lamp will remain illuminated approximately 3 seconds after the last door closes. When the driver places the dome lamp switch in the OFF position, the dome lamp will be disabled. In the event that the dome lamp were to remain illuminated for more than 10 minutes with the ignition switch in the OFF position and no doors opened, the BCM will deactivate the dome lamp control circuit to prevent total battery discharge.

Battery voltage must be between 9-16 V.

DTC B2555 01

  1. The BCM detects a short to voltage in the dome lamp switch Cancel signal circuit.
  2. The BCM detects a short to voltage in the dome lamp switch ON signal circuit.

DTC B2555 02

  1. The BCM detects a short to ground in the dome lamp switch Cancel signal circuit.
  2. The BCM detects a short to ground in the dome lamp switch ON signal circuit.

DTC B2555 04

  1. The BCM detects an open/high resistance in the dome lamp switch Cancel signal circuit.
  2. The BCM detects an open/high resistance in the dome lamp switch ON signal circuit.

The dome lamps cannot be turned off when any door is in the open or ajar position.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the E37F dome/reading lamps-front. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 6 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Interior/Courtesy Lighting Master Switch parameter is Door. If Cancel Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 4 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If On Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 5 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Door
  5. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the ground circuit terminal 6.
  6. Verify the scan tool Interior/Courtesy Lighting Master Switch parameter is Cancel. If not Cancel Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 4 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Cancel
  7. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the ground circuit terminal 6.
  8. Verify the scan tool Interior/Courtesy Lighting Master Switch parameter is On. If not On Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 5 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If On
  9. Test or replace the E37F dome/reading lamps-front.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Dome and Reading Lamp Replacement - Front»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F24DA Fuse B+11
Rear Compartment Courtesy Lamp ControlB2570 0211
Rear Compartment Courtesy Lamp Ground1
1. Rear Compartment Lamp Malfunction

The body control module (BCM) applies battery voltage to the rear compartment courtesy lamp through the rear compartment lamp control circuit. When the BCM receives a rear compartment lid open input from the rear compartment lid latch, the BCM applies battery voltage to the rear compartment lamp control circuit illuminating the rear compartment courtesy lamp. In the event that the rear compartment lamp were to remain illuminated for more than 10 minutes with the ignition switch in the OFF position and no doors opened, the BCM will deactivate the rear compartment lamp control circuit to prevent total battery discharge.

  1. Battery voltage must be between 9-16 V.
  2. Rear compartment OPEN.

The BCM detects a short to ground on the rear compartment courtesy lamp control circuit.

The rear compartment lamp is inoperative.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, exterior lamps OFF, trunk latch latched, disconnect the harness connector at the E8S rear compartment courtesy lamp.
  2. Test for less than 10 ohms between the ground circuit terminal 2 and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Connect a test lamp between the control circuit terminal 1 and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the Trunk Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the E8S rear compartment courtesy lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Cargo Center Courtesy Lamp Bulb Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F9DA Fuse B+B2699 01, B2699 04B2699 01, B2699 04
F23DA Fuse B+B2575 01, B2575 04B2575 01, B2575 04
Low Beam Headlamp Control - Left (T4A)B2575 02B2575 01, B2575 041
Low Beam Headlamp Control - Right (T4A)B2699 02B2699 01, B2699 041
Headlamp Ground - Left1
Headlamp Ground - Right1
1. Headlamps Malfunction

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the headlamp switch. The body control module (BCM) responds by applying battery positive voltage to the left and right low beam headlamp control circuits illuminating the low beam headlamps.

  1. Battery voltage must be between 9-16 V.
  2. Low beam headlamps ON.

DTC B2575 01 and B2575 04

  1. The BCM detects an open/high resistance in the left low beam headlamp control circuit.
  2. The BCM detects a short to ground or an open/high resistance in the F23DA fuse B+ circuit.

DTC B2575 02

The BCM detects a short to ground in the left low beam headlamp control circuit.

DTC B2699 01 and B2699 04

  1. The BCM detects an open/high resistance in the right low beam headlamp control circuit.
  2. The BCM detects a short to ground or an open/high resistance in the F9DA fuse B+ circuit.

DTC B2699 02

The BCM detects a short to ground in the right low beam headlamp control circuit.

  1. When DTC B2575 sets, the left low beam headlamp will be inoperative.
  2. When DTC B2699 sets, the right low beam headlamp will be inoperative.
  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

  1. «Headlights/Daytime Running Lights (DRL) Schematics»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-wiring-schematic-diagrams)
  2. «Body Control System Schematics»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#data-communications-system)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

DTC B2575

  1. Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 3 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF, remove the F23DA fuse at the X51A fuse block - instrument panel. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF, remove the F23DA fuse at the X51A fuse block - instrument panel. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X1 harness connector at the K9 body control module.
  4. Install the F23DA fuse.
  5. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the E4G headlamp - left low beam.
  6. Test for less than 5 ohms between the ground circuit terminal B and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  7. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  8. Verify the test lamp turns ON and OFF when commanding the Left Low Beam/Daytime Running Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  9. Test or replace the E4G headlamp - left low beam.

DTC B2699

  1. Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 2 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF, remove the F9DA fuse at the X51A fuse block - instrument panel. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF, remove the F9DA fuse at the X51A fuse block - instrument panel. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X1 harness connector at the K9 body control module.
  4. Install the F9DA fuse.
  5. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the E4F headlamp - right low beam.
  6. Test for less than 5 ohms between the ground circuit terminal B and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  7. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  8. Verify the test lamp turns ON and OFF when commanding the Right Low Beam/Daytime Running Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  9. Test or replace the E4F headlamp - right low beam.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Headlamp Bulb Replacement (TT4 Low Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT4 High Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Headlamp Switch Park Lamps ON Signal2B257A 002
Headlamp Switch Headlamps OFF SignalB257A 0011
Headlamp Switch Headlamps ON SignalB257A 0011
Headlamp Switch Ground1
1. Headlamps Malfunction 2. Park, License, and/or Tail Lamps Malfunction

For headlamp operation, the body control module (BCM) monitors three signal circuits from the headlamp switch. When the headlamp switch is in the AUTO position, the three signal circuits are unaffected and the BCM relies on the ambient light sensor input to turn the headlamps and daytime running lamps (DRLs) ON and OFF. When the headlamp switch is placed in the OFF position, the headlamp switch headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the headlamp switch in the PARK LAMPS position, the headlamp switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the headlamp switch is in the HEADLAMP position, both the headlamp switch park lamps ON signal circuit and the headlamp switch headlamps ON signal circuit are grounded. The BCM responds by commanding the park lamps and headlamps ON.

Battery voltage must be between 9-16 V.

  1. The BCM detects an open/high resistance in the headlamp switch park lamps ON signal circuit.
  2. The BCM detects a short to ground in the headlamp switch headlamps ON signal circuit.
  3. The BCM detects a short to ground in the headlamp switch headlamps OFF signal circuit.
  1. When DTC B257A 00 is present on the headlamp switch headlamps OFF signal circuit, the low beam headlamps are always ON in the AUTO position. The headlamp switch operates in all positions other than AUTO. The AUTO headlamp defeat is inoperative.
  2. When DTC B257A 00 is present on the headlamp switch headlamps ON signal circuit, the low beam headlamps are always ON. The BCM disregards all headlamp switch inputs.
  3. When DTC B257A 00 is present on the headlamp switch park lamps ON signal circuit, the park lamps and low beam headlamps are inoperative in the PARK and HEAD positions. Headlamps and park lamps operate in AUTO position.
  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, all doors closed, all accessories OFF, disconnect the harness connector at the S30 headlamp switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 6 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Automatic Headlamps Disable Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 5 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the ground circuit terminal 6.
  6. Verify the scan tool Automatic Headlamps Disable Switch parameter is Active. If not Active Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 5 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Verify the scan tool Park Lamps Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 3 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  8. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the ground circuit terminal 6.
  9. Verify the scan tool Park Lamps Switch parameter is Active. If not Active Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 3 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  10. Verify the scan tool Headlamps On Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 4 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  11. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the ground circuit terminal 6.
  12. Verify the scan tool Headlamps On Switch parameter is Active. If not Active Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 4 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  13. Test or replace the S30 headlamp switch.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Headlamp Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Instrument Panel Dimmer Switch B+B1405 03, B1529 03, B257B 03B257B 03
Instrument Panel Dimmer Switch SignalB257B 03B257B 03B257B 07
LED Backlight Dimming Control Terminal 8 X2B2610 02B2610 041
LED Backlight Dimming Control Terminal 9 X7B2610 02B2610 041
Hazard Warning Switch LED Backlight Dimming ControlB096A 02B096A 01, B096A 041
1. Interior Backlighting Malfunction

The instrument panel dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The instrument panel dimmer switch provides a voltage signal to the body control module (BCM) that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The BCM provides B+ and a low reference signal to the instrument panel dimmer switch. When the instrument panel dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies a pulse width modulated (PWM) voltage through the LED dimming control circuits illuminating the interior backlighting to the requested level of brightness.

  1. Battery voltage must be between 9-16 V.
  2. Park Lamps ON.

DTC B257B 03

  1. The BCM detects a short to ground or an open/high resistance in the instrument panel dimmer switch B+ circuit.
  2. The BCM detects a short to ground or an open/high resistance in the instrument panel dimmer switch signal circuit.

DTC B257B 07

The BCM detects a short to voltage in the instrument panel dimmer switch signal circuit.

The BCM will not dim any interior backlighting. All interior backlighting will default to the level selected prior to the fault being present.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the S30 headlamp switch, ignition ON.
  2. Test for B+ between the B+ circuit terminal 1 and ground. If less than B+ Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If B+
  3. Verify the scan tool LED Backlight Dimming Command parameter is greater than 40%. If 40% or less Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 12 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If greater than 40%
  4. Install a 3 A fused jumper wire between the signal circuit terminal 12 and the B+ circuit terminal 1.
  5. Verify the scan tool LED Backlight Dimming Command parameter is less than 30%. If 30% or greater Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If less than 30%
  6. Test or replace the S30 headlamp switch.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Headlamp Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The headlamp control module calculates the headlamp angle and sends commands to the left and right adaptive forward lighting system headlamp actuators. The headlamp actuators drive the headlamps to the position commanded by the headlamp control module. The headlamp control module monitors the headlamp actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory and the driver will be notified with a "Service AFL Lamp" message displayed over the driver information center located on the instrument cluster.

  1. Engine ON.
  2. Headlamps ON.

DTC B257C 00

The headlamp control module receives a serial data message from the left headlamp internal logic module that an internal headlamp malfunction has occurred.

DTC B257D 00

The headlamp control module receives a serial data message from the right headlamp internal logic module that an internal headlamp malfunction has occurred.

  1. Service AFL Lamp message is commanded ON.
  2. The appropriate headlamp horizontal and vertical controls are disabled.
  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 50 malfunction-free ignition cycles have occurred.

Diagnostic Aids

DTC B257C and B257D will set when there is an internal malfunction within the left or right headlamp assemblies. No parts are serviceable within the headlamp assemblies so complete headlamp assembly replacement is necessary.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, with a scan tool, clear the DTC and operate the vehicle within the Conditions for Running the DTC. Verify the DTC does not reset. If the DTC resets as current, replace the appropriate headlamp assembly.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Headlamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for headlamp control module replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Headlamp High Beam Relay ControlB2580 02, B2580 04B2580 02, B2580 04B2580 01
High Beam Headlamp Control - Left111
High Beam Headlamp Control - Right111
Headlamp Ground - Left1
Headlamp Ground - Right1
1. Headlamps Malfunction

The high beam and flash to pass functions are contained within the turn signal/multifunction switch. The BCM provides the turn signal/multifunction switch with two signal circuits, the high beam signal circuit and the flash to pass signal circuit. When the low beam headlamps are ON and the turn signal/multifunction switch is placed in the high beam position, ground is applied to the BCM through the high beam signal circuit. The BCM responds to the high beam request by applying ground to the high beam relay control circuit which energizes the high beam relay. With the high beam relay energized, the switch contacts close allowing battery voltage to flow through the high beam fuses to the high beam control circuits illuminating the high beam headlamps.

  1. Battery voltage must be between 9-16 V.
  2. High beam headlamps ON.

DTC B2580 01

The BCM detects a short to voltage in the headlamp high beam relay control circuit.

DTC B2580 02

The BCM detects a short to ground in the headlamp high beam relay control circuit.

DTC B2580 04

The BCM detects an open in the headlamp high beam relay control circuit.

The high beam headlamps and flash to pass will not operate.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, disconnect the X2 harness connector at the X50A fuse block - underhood.
  2. Connect a test lamp between the control circuit terminal 58 and B+, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the High Beams ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Test or replace the X50A fuse block - underhood.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Fuse Block Replacement»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F3DA (BCM 5) Fuse B+B2585 01, B2585 04B2585 01, B2585 04
F24DA (BCM 2) Fuse B+B3867 01, B3867 04B3867 01, B3867 04
Headlamp Switch Park Lamps ON Signal2B257A 002
Park Lamps Control - LeftB2585 02B2585 01, B2585 04B2585 01, B2585 04
Park Lamps Control - RightB3867 02B3867 01, B3867 04B3867 01, B3867 04
Headlamp Switch Ground2
Park/Turn Signal Lamp Ground - Left Front1
Park/Turn Signal Lamp Ground - Right Front1
Side Marker Lamp Ground - Left Front1
Side Marker Lamp Ground - Left Rear1
Side Marker Lamp Ground - Right Front1
Side Marker Lamp Ground - Right Rear1
Tail Lamp Ground - Left1
Tail Lamp Ground - Right1
1. Park, License, and/or Tail Lamps Malfunction 2. Park Lamp Switch Malfunction

When the headlamp switch is placed in the HEAD or PARK position, ground is applied to the park lamp switch ON signal circuit to the body control module (BCM). The BCM responds by applying voltage to the park lamps, tail lamps, and license lamps control circuits illuminating the park, tail, and license lamps.

  1. Battery voltage must be between 9-16 V.
  2. Park lamps ON.

DTC B2585 01 and B2585 04

  1. The BCM detects a short to voltage or an open/high resistance in the left park lamps control circuit.
  2. The BCM detects a short to ground or an open/high resistance in the F3DA (BCM 5) fuse B+ circuit.

DTC B2585 02

The BCM detects a short to ground in the left park lamps control circuit.

DTC B3867 01 and B3867 04

  1. The BCM detects a short to voltage or an open/high resistance in the right park lamps control circuit.
  2. The BCM detects a short to ground or an open/high resistance in the F24DA (BCM 2) fuse B+ circuit.

DTC B3867 02

The BCM detects a short to ground in the right park lamps control circuit.

DTC B2585 01

The left park lamps are always ON.

DTC B2585 02 and B2585 04

The left park lamps are always OFF.

DTC B3867 01

The right park lamps are always ON.

DTC B3867 02 and B3867 04

The right park lamps are always OFF.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

  1. «Exterior Lights Schematics»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-wiring-schematic-diagrams)
  2. «Body Control System Schematics»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#data-communications-system)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

DTC B2585

  1. Ignition OFF, disconnect the X2 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 3 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X2 harness connector at the K9 body control module.
  4. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate left park lamp.
  5. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground. E4N park/turn signal lamp - left terminal G E13L headlamp - left terminal A (with T4A) E13L headlamp - left terminal J (with T4F) E5E tail lamp - left terminal A If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  6. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON. E4N park/turn signal lamp - left terminal B E13L headlamp - left terminal D (with T4A) E13L headlamp - left terminal F (with T4F) E5E tail lamp - left terminal E
  7. Verify the test lamp turns ON and OFF when commanding the Left Park Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  8. Test or replace the appropriate left park lamp.

DTC B3867

  1. Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 4 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X1 harness connector at the K9 body control module.
  4. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate right park lamp.
  5. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground. E4P park/turn signal lamp - right terminal G E13R headlamp - right terminal A (with T4A) E13R headlamp - right terminal J (with T4F) E5F tail lamp - right terminal A If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  6. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON. E4P park/turn signal lamp - right terminal B E13R headlamp - right terminal D (with T4A) E13R headlamp - right terminal F (with T4F) E5F tail lamp - right terminal E
  7. Verify the test lamp turns ON and OFF when commanding the Right Park Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  8. Test or replace the appropriate right park lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Headlamp Bulb Replacement (TT4 Low Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT4 High Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Tail Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Front Turn Signal Lamp Bulb Replacement (TT4)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Headlamp Low Beam Relay ControlB258A 02, B258A 04B258A 02, B258A 04B258A 01
Low Beam Headlamp Control - Left111
Low Beam Headlamp Control - Right111
Headlamp Ground - Left1
Headlamp Ground - Right1
1. Headlamps Malfunction

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the headlamp switch. The body control module (BCM) responds by applying ground to the low beam relay control circuit which energizes the low beam relay. With the low beam relay energized, the switch contacts close allowing battery voltage to flow through the low beam fuses to the low beam control circuits illuminating the low beam headlamps.

  1. Battery voltage must be between 9-16 V.
  2. Low beam headlamps ON.

DTC B258A 01

The BCM detects a short to voltage in the headlamp low beam relay control circuit.

DTC B258A 02

The BCM detects a short to ground in the headlamp low beam relay control circuit.

DTC B258A 04

The BCM detects an open in the headlamp low beam relay control circuit.

DTC B258A 01 or B258A 04

The low beam headlamps will not operate.

DTC B258A 02

The low beam headlamps will always be ON.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, disconnect the KR49 headlamp low beam relay.
  2. Connect a test lamp between the control circuit terminal 85 and B+, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Low Beams ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the control circuit terminal and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Test or replace the KR49 headlamp low beam relay.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Relay Replacement (Within an Electrical Center)»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Left Daytime Running Lamp ControlB2600 02B2600 04B2600 01
Left Daytime Running Lamp/Front Side Marker GroundB2585 04, B2600 04

When the headlight switch is in the Auto position and the ambient light sensor detects sunlight, the body control module (BCM) will command the daytime running lamps to illuminate by providing 12 volts to the daytime running lamp control circuit.

  1. The engine is running.
  2. Headlamp switch in AUTO position.
  3. The ambient light is day.

B2600 01

The BCM detects a short to voltage on the daytime running lamp control circuit.

B2600 02

The BCM detects a short to ground on the daytime running lamp control circuit.

B2600 04

The BCM detects an open daytime running lamp control circuit.

Action Taken When the DTC Sets

For B2600 01, the left daytime running lamp will be continuously illuminated.

For B2600 02 or B2600 04, the left daytime running lamp will be inoperative.

  1. The DTC will be current for as long as the fault is present.
  2. When the fault is no longer present, the DTC will be a history DTC.
  3. A history DTC will clear after 50 ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, command the Left Dedicated Daytime Running Lamp ON and OFF with a scan tool. The E4C daytime running lamp - left should turn ON and OFF when changing between the commanded states.

  1. Ignition OFF, disconnect the X1 harness connector K9 BCM.
  2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 3 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the X1 harness connector at the K9 BCM.
  4. Ignition OFF, disconnect the harness connector at the E4C daytime running lamp - left.
  5. Test for less than 30 ohms between the ground circuit harness connector terminal G and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
  6. Connect a test lamp between the control circuit terminal A and ground.
  7. Ignition ON, command the Left Dedicated Daytime Running Lamp ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  8. If all circuits test normal, replace the daytime running lamp bulb.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Daytime Running Lamp Bulb Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Right Daytime Running Lamp ControlB2605 02B2605 04B2605 01
Right Daytime Running Lamp/Front Side Marker GroundB2605 01, B2605 04, B3867 01, B3867 04, B3949 01, B3949 04

When the headlight switch is in the Auto position and the ambient light sensor detects sunlight, the body control module (BCM) will command the daytime running lamps to illuminate by providing 12 volts to the daytime running lamp control circuit.

  1. The engine is running.
  2. Headlamp switch in AUTO position.
  3. The ambient light is day.

B2605 01

The BCM detects a short to voltage on the right daytime running lamp control circuit.

B2605 02

The BCM detects a short to ground on the right daytime running lamp control circuit.

B2605 04

The BCM detects an open/high resistance on the right daytime running lamp control circuit or the right daytime running lamp ground circuit.

For B2605 01, the right daytime running lamp will be continuously illuminated.

For B2605 02 or B2605 04, the right daytime running lamp will be inoperative.

  1. The DTC will be current for as long as the fault is present.
  2. When the fault is no longer present, the DTC will be a history DTC.
  3. A history DTC will clear after 50 ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the Right Dedicated Daytime Running Lamp ON and OFF with a scan tool. The E4D daytime running lamp - right should turn ON and OFF when changing between the commanded states.

  1. Ignition OFF, disconnect the X1 harness connector K9 BCM.
  2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 2 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the X1 harness connector at the K9 BCM
  4. Ignition OFF, disconnect the harness connector at the E4D daytime running lamp - right.
  5. Test for less than 30 ohms between the ground circuit harness connector terminal G and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
  6. Connect a test lamp between the control circuit terminal A and ground.
  7. Command the Right Dedicated Daytime Running Lamp ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  8. If all circuits test normal, replace the daytime running lamp bulb.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Daytime Running Lamp Bulb Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Left Daytime Running Lamp Relay ControlB260B 02B260B 04B260B 01
Right Daytime Running Lamp Relay ControlB260C 02B260C 04B260C 01

The body control module (BCM) receives a signal from the ambient light/sunload sensor indicating a low or high ambient outside light level. Under daylight conditions the BCM supplies a battery voltage to the daytime running lamps (DRL).

B260B 01 or B260C 01

Engine is not running.

B260B 02, B260C 02, B260B 04 or B260C 04

  1. The engine is running.
  2. Headlamp switch in AUTO position.
  3. The ambient light is day.

B260B 01 or B260C 01

The BCM detects a short to voltage on the appropriate daytime running lamp control circuit.

B260B 02 or B260C 02

The BCM detects a short to ground on the appropriate daytime running lamp control circuit.

B260B 04 or B260C 04

The BCM detects an open circuit on the appropriate daytime running lamp control circuit.

The appropriate headlamp is inoperative.

The condition responsible for setting the DTC no longer exists.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the appropriate Daytime Running Lamp ON and OFF with a scan tool. The daytime running lamp should turn ON and OFF when changing between the selected states.

  1. Ignition OFF, disconnect the harness connector at the appropriate E13 headlamp.
  2. Test for less than 5 ohms between the ground circuit terminal G and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal A and ground.
  4. Command the appropriate Daytime Running Lamp ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM. If the test lamp is always OFF, test the Signal circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the K9 BCM.
  5. If all the circuits test normal, replace the E13 headlamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Headlamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Headlamp Bulb Replacement (TT4 Low Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT4 High Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Instrument Panel Dimmer Switch B+B1405 03, B1529 03, B257B 03B257B 03
Instrument Panel Dimmer Switch SignalB257B 03B257B 03B257B 07
LED Backlight Dimming Control Terminal 8 X2B2610 02B2610 042
LED Backlight Dimming Control Terminal 9 X7B2610 02B2610 042
Object Detection Switch Indicator LED Backlight Dimming Control Terminal 5 X1B2625 0222
Dome/Reading Lamps - Front Ground2
Dome/Reading Lamps - 2nd Row Ground2
Garage Door Opener Ground2
Headlamp Switch Ground1
Head - Up Display Switch Ground2
Ignition Mode Switch Ground2
Multifunction Switch 1 - Instrument Panel Ground2
Multifunction Switch 2 - Instrument Panel Ground2
Outside Rearview Mirror Switch Ground2
Park Brake Control Switch Ground2
Sunroof Switch Ground2
Sunroof Sunshade Switch Ground2
Steering Wheel Controls Switch - Left Ground2
Steering Wheel Controls Switch - Right Ground2
Window Switch - Passenger Ground2
1. Dimmer Switch Malfunction 2. Interior Backlighting Malfunction

The instrument panel dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The instrument panel dimmer switch provides a voltage signal to the body control module (BCM) that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The BCM provides a low reference signal and a B+ reference circuit to the instrument panel dimmer switch. When the instrument panel dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies a pulse width modulated (PWM) voltage through the LED dimming control circuits illuminating the interior backlighting to the requested level of brightness.

  1. Battery voltage must be between 9-16 V.
  2. Park lamps ON.

DTC B2610 02

The BCM detects a short to ground in the LED backlight dimming control circuit terminal 8 X2 or terminal 9 X7.

DTC B2610 04

The BCM detects an open/high resistance in the LED backlight dimming control circuit terminal 8 X2 or terminal 9 X7.

The BCM will disable the LED backlight dimming control circuits.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, all doors closed, all accessories OFF, disconnect the harness connector at the component with inoperative backlighting. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the appropriate ground circuit terminal and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Connect a test lamp between the appropriate control circuit terminal and ground.
  4. Verify the test lamp turns ON and OFF when commanding the LED Backlight Dimming ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X2 and X7 harness connectors at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X2 and X7 harness connectors at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the component with inoperative backlighting.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Dome and Reading Lamp Replacement - Front»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Dome and Reading Lamp Replacement - Rear»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Sunroof Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/sun-rooft-topconvertible-top/#sunroof-system)
  4. «Outside Remote Control Rearview Mirror Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/mirrors/#mirror-system)
  5. «Front Side Door Window and Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/heated-glassdefoggers/#fixed-and-moveable-windows)
  6. «Rear Side Door Window Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/heated-glassdefoggers/#fixed-and-moveable-windows)
  7. «Headlamp Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  8. «Parking Brake Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/parking-brake-system/#parking-brake-system)
  9. «Instrument Panel Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
  10. «Accessory Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
  11. «Radio and Telephone Control Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/entertainment-systems/#cellular-system-entertainment-system-and-navigation-system)
  12. «Cruise Control Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/cruise-control-systems/#cruise-control-system)
  13. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, HVAC, instrument cluster, or radio replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Dome/Courtesy Lamps Control - Terminal 1 X7B2615 0211
Dome/Reading Lamps - Front Ground1
Dome/Reading Lamps - 2nd Row Ground1
Door Courtesy Lamp - Driver Ground1
Door Courtesy Lamp - Passenger Ground1
Door Courtesy Lamp - Left Rear Ground1
Door Courtesy Lamp - Right Rear Ground1
Instrument Panel Courtesy Lamp - Left Ground1
Instrument Panel Courtesy Lamp - Right Ground1
1. Dome Lamps Malfunction

The dome lamp switch has 3 positions: DOOR, OFF, and ON. The ON position provides a ground for continuous operation and the dome/courtesy lamps will remain illuminated until the switch is placed in either the DOOR or OFF position. When in the DOOR position, the dome lamps operation is controlled by the body control module (BCM). When any door is opened, the door ajar switch contacts close and the BCM receives a door-open input. The BCM illuminates the dome lamps, door courtesy lamps, and instrument panel courtesy lamps when any door is opened or a door lock/unlock request is activated with the key fob. After all doors have been closed, the dome lamps, door courtesy lamps, and instrument panel courtesy lamps will remain illuminated approximately 3 seconds after the last door closes. When the driver places the dome lamp switch in the OFF position, the dome/courtesy lamps will be disabled. In the event that the dome/courtesy lamps were to remain illuminated for more than 10 minutes with the ignition switch in the OFF position and no doors opened, the BCM will deactivate the dome/courtesy lamps control circuit to prevent total battery discharge.

Battery voltage must be between 9-16 V.

The BCM detects a short to ground in the dome lamps control circuit.

The BCM will disable the dome lamps control circuit.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, all doors closed, all accessories OFF, disconnect the harness connectors at the components listed below. E37F dome/reading lamps - front E37B dome/reading lamps - 2nd row E8D door courtesy lamp - driver E8P door courtesy lamp - passenger E8LR door courtesy lamp - left rear E8RR door courtesy lamp - right rear E8J instrument panel courtesy lamp - left E8K instrument panel courtesy lamp - right
  2. Test for less than 10 ohms between the appropriate ground circuit terminal listed below and ground. E37F dome/reading lamps - front terminal 6 E37B dome/reading lamps - 2nd row terminal 6 E8D door courtesy lamp - driver terminal 2 E8P door courtesy lamp - passenger terminal 2 E8LR door courtesy lamp - left rear terminal 2 E8RR door courtesy lamp - right rear terminal 2 E8J instrument panel courtesy lamp - left terminal 2 E8K instrument panel courtesy lamp - right terminal 2 If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground. E37F dome/reading lamps - front terminal 2 E37B dome/reading lamps - 2nd row terminal 2 E8D door courtesy lamp - driver terminal 1 E8P door courtesy lamp - passenger terminal 1 E8LR door courtesy lamp - left rear terminal 1 E8RR door courtesy lamp - right rear terminal 1 E8J instrument panel courtesy lamp - left terminal 1 E8K instrument panel courtesy lamp - right terminal 1
  4. Verify the test lamp turns ON and OFF when commanding the Courtesy Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate dome/courtesy lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Dome and Reading Lamp Replacement - Front»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Dome and Reading Lamp Replacement - Rear»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Front Side Door Warning Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Rear Side Door Warning Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Object Detection Switch Indicator LED Backlight Dimming Control Terminal 5 X1B2625 0211
1. Interior Backlighting Malfunction

The instrument panel dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The instrument panel dimmer switch provides a voltage signal to the body control module (BCM) that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The BCM provides a low reference signal and B+ to the instrument panel dimmer switch. When the instrument panel dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies a pulse width modulated (PWM) voltage through the LED backlight dimming control circuit illuminating the LED backlighting to the requested level of brightness.

  1. Battery voltage must be between 9-16 V.
  2. Park lamps ON.

The BCM detects a short to ground in the LED backlight dimming control circuit terminal 5 X1.

The LED backlight dimming control circuit driver is shut down.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, disconnect the harness connector at the S48D multifunction switch 2 - instrument panel.
  2. Connect a test lamp between the control circuit terminal 3 and ground.
  3. Verify the test lamp turns ON and OFF when commanding the LED Backlight Dimming ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Test or replace the S48D multifunction switch 2 - instrument panel.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Accessory Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Exterior Courtesy Lamps ControlB263A 02B263A 041
Outside Rearview Mirror - Driver Ground1
Outside Rearview Mirror - Passenger Ground1
1. Exterior Courtesy Lamps Malfunction

The body control module (BCM) supplies battery voltage to the exterior courtesy LED lighting located under each outside rearview mirror for approach lighting. When the keyless entry transmitter is operated to the lock/unlock functions the exterior door handles LED and the LED lighting located under each outside rearview mirror for approach lighting are commanded ON.

  1. Battery voltage must be between 9-16 V.
  2. Park lamps ON.

DTC B263A 02

The BCM detects a short to ground in the exterior courtesy lamps control circuit.

DTC B263A 04

The BCM detects an open/high resistance in the exterior courtesy lamps control circuit.

The BCM will disable the exterior courtesy lamps control circuit.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, all doors closed, all accessories OFF, disconnect the harness connectors at the A9A outside rearview mirror - driver and the A9B outside rearview mirror - passenger. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the appropriate ground circuit terminal 4 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Connect a test lamp between the control circuit terminal 17 and ground.
  4. Verify the test lamp turns ON and OFF when commanding the Outside Rear View Mirror Courtesy Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate door courtesy lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Outside Rearview Mirror Replacement»(/buick/lacrosse/ii-2009-2013/remont/mirrors/#mirror-system)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F9DA Fuse B+11
F23DA Fuse B+11
Ambient Light Sensor SignalB2645 03B2645 07B2645 07
Daytime Running Lamp Control - Left (T4F)B2600 02B2600 04B2600 01
Daytime Running Lamp Control - Right (T4F)B2605 02B2605 04B2605 01
Ambient Light Sensor Low ReferenceB2645 071
Daytime Running Lamp Ground - Left (T4F)1
Daytime Running Lamp Ground - Right (T4F)1
1. Daytime Running Lamps Malfunction

The ambient light sensor is used to monitor outside lighting conditions. The body control module (BCM) provides a 5-volt reference signal to the ambient light sensor. Depending on outside lighting conditions, the ambient light sensor provides a voltage signal to the BCM that will vary between 0.2 and 4.9 volts. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic headlamp system control when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying voltage to the DRL control circuits illuminating the DRLs. Any function or condition that turns on the headlamps will cancel DRL operation.

Battery voltage must be between 9-16 V.

DTC B2645 03

The BCM detects a short to ground in the ambient light sensor signal circuit.

DTC B2645 07

  1. The BCM detects a short to voltage or an open/high resistance in the ambient light sensor signal circuit.
  2. The BCM detects an open/high resistance in the ambient light sensor low reference circuit.
  1. Automatic headlamp system and daytime running lamps are inoperative.
  2. The BCM defaults to low light status and commands the low beam headlamps ON.
  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector at the B10B ambient light/sunload sensor. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the low reference circuit terminal 6 and ground. If 15 ohms or greater Ignition OFF, disconnect the X2 harness connector at the K33 HVAC control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K33 HVAC control module. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Ambient Light Sensor parameter is greater than 4.65 V. If 4.65 V or less Ignition OFF, disconnect the X2 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 5 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If greater than 4.65 V
  5. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the low reference circuit terminal 6.
  6. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 V. If 0.196 V or greater Ignition OFF, disconnect the X2 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 5 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If less than 0.196 V
  7. Test or replace the B10B ambient light/sunload sensor.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Sun Load Temperature and Headlamp Automatic Control Ambient Light Sensor Replacement»(/buick/lacrosse/ii-2009-2013/remont/automatic-hvac-system/#hvac-system-automatic)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Accent Lamp Control - Terminal 7 X6B2652 0211
Accent Lamp - Driver Door Ground1
Accent Lamp - Driver Door Handle Ground1
Accent Lamp - Passenger Door Ground1
Accent Lamp - Passenger Door Handle Ground1
Accent Lamp - Left Instrument Panel Ground1
Accent Lamp - Lower Instrument Panel Ground1
Accent Lamp - Right Instrument Panel Ground1
Accent Lamp - Right Rear Door Ground1
Accent Lamp - Right Rear Door Handle Ground1
Accent Lamp - Left Rear Door Ground1
Accent Lamp - Left Rear Door Handle Ground1
Accent Lamp - Center Console Armrest Left Ground1
Accent Lamp - Center Console Armrest Right Ground1
Accent Lamp - Center Console Cupholder Left Ground1
Accent Lamp - Center Console Cupholder Right Ground1
1. Interior Accent Lighting Malfunction

The instrument panel dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The instrument panel dimmer switch provides a voltage signal to the body control module (BCM) that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The BCM provides a low reference signal and B+ to the instrument panel dimmer switch. When the instrument panel dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies a pulse width modulated (PWM) voltage through the LED dimming control circuits illuminating the interior backlighting to the requested level of brightness.

  1. Battery voltage must be between 9-16 V.
  2. Park lamps ON.

The BCM detects a short to ground in the accent lamps control circuit.

The BCM will disable the accent lamps control circuit.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the appropriate E1 accent lamp. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the appropriate ground circuit terminal and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Connect a test lamp between the appropriate control circuit terminal and ground.
  4. Verify the test lamp turns ON and OFF while turning the headlamp switch ON and OFF. If the test lamp is always OFF Ignition OFF, disconnect the X6 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X6 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate E1 accent lamp

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Front Floor Console Cup Holder Illumination Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Front Floor Console Armrest Compartment Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Front Side Door Inside Handle Illumination Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Rear Side Door Inside Handle Illumination Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Lighting Control Switch ReferenceB1405 03, B1529 03, B2740 00B257B 031
Lighting Control Switch SignalB257B 03B257B 031
1. Front Fog Switch Malfunction

The front fog lamp relay is supplied with battery voltage at all times. The front fog lamp switch signal circuit is grounded momentarily by pressing the front fog lamp switch. The body control module (BCM) energizes the front fog lamp relay by applying ground to the front fog lamp relay control circuit. When the front fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the front fog lamp fuse to the front fog lamp supply voltage circuit which illuminates the front fog lamps.

  1. The ignition is turned ON.
  2. Front fog lamp switch activated.

The BCM detects the fog lamp switch is continuously active.

Front fog lamps will be continuously illuminated.

  1. The DTC will be current for as long as the fault is present.
  2. When the fault is no longer present, the DTC will be a history DTC.
  3. A history DTC will clear after 50 ignition cycles.

The condition for setting the DTC is not longer present.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool Front Fog Lamps Switch parameter while turning the front fog lamps switch ON and OFF. The parameter should change between Active and Inactive.

  1. Ignition OFF, disconnect the harness connector at the S30 headlamp switch.
  2. Ignition ON, test for greater than 10 V between the 12 V reference circuit terminal 1 and ground. If less than the specified range, test the 12 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  3. Test for 0.4k-1k ohms between the signal circuit terminal 12 and ground. If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM. If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the K9 BCM.
  4. If all circuits test normal, test or replace the S30 headlamp switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Headlamp Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Left Rear Stop Lamp ControlB3445 021B3445 01
Right Rear Stop Lamp ControlB3878 0223
1. Left Rear Stop Lamp Inoperative 2. Right Rear Stop Lamp Inoperative 3. Right Rear Stop Lamp Always ON

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal to the body control module (BCM). The BCM will apply battery voltage to the right, left and center stop lamp control circuits.

Brake pedal is applied.

B3445 01

The BCM detects a short to voltage on the left rear brake lamp control circuit.

B3445 02

The BCM detects a short to ground on the left rear brake lamp control circuit.

B3878 02

The BCM detects a short to ground on the right rear brake lamp control circuit.

B3445 01

The left rear brake lamp will be continuously illuminated.

B3445 02

The left rear brake lamp will be inoperative.

B3878 02

The right rear brake lamp will be inoperative.

  1. The DTC will be current for as long as the fault is present.
  2. When the fault is no longer present, the DTC will be a history DTC.
  3. A history DTC will clear after 50 ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, observe the function of the E5AA tail/stop lamp-left while commanding the Left Brake Lamp ON and OFF with a scan tool. The E5AA tail/stop lamp-left should turn ON and OFF while changing between the commanded states. If the E5AA tail/stop lamp-left is always ON or always OFF, refer to Left Brake Lamp Malfunction below.
  2. Observe the function of the E5AB tail/stop lamp-right while commanding the Right Brake Lamp ON and OFF with a scan tool. The E5AB tail/stop lamp-right should turn ON and OFF while changing between the commanded states. If the E5AB tail/stop lamp-right is always ON or always OFF, refer to Right Brake Lamp Malfunction below.

Left Brake Lamp Malfunction

  1. Ignition OFF, disconnect the X409 inline harness connector at the E5E tail lamp-left.
  2. Test for less than 30 ohms between the ground circuit terminal A and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal D and ground.
  4. Ignition ON, command the Left Brake Lamp ON and OFF with a scan tool, the test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  5. If all circuits test normal, test or replace the E5E tail lamp-left.

Right Brake Lamp Malfunction

  1. Ignition OFF, disconnect the X410 inline harness connector at the E5F tail lamp-right.
  2. Test for less than 30 ohms between the ground circuit terminal A and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal D and ground.
  4. Ignition ON, command the Right Brake Lamp ON and OFF with a scan tool, the test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  5. If all circuits test normal, test or replace the E5F tail lamp-right.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Tail Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Hazard Warning Switch Signal111B3596 00
Hazard Warning Switch LED Backlighting Control222
Hazard Warning Switch Ground1
1. Hazard Lamps Malfunction 2. Hazard Warning Switch Backlighting Malfunction

The hazard flashers may be activated in any power mode. The hazard warning switch signal circuit is momentarily grounded when the hazard warning switch is pressed. The body control module (BCM) responds to the hazard warning switch signal input by supplying battery voltage to all four turn signal lamps in an ON and OFF duty cycle. When the hazard warning switch is activated, the BCM sends a serial data message to the instrument cluster requesting both turn signal indicators to be cycled ON and OFF.

  1. Battery voltage must be between 9-16 V.
  2. Hazard lamps ON.

The hazard warning switch input is Active for longer than 60 seconds.

The hazard lamps are inoperative.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S48C multifunction switch 1 - instrument panel. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 7 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Hazard Lamps Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X2 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 10 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 10 and ground.
  6. Verify the scan tool Hazard Lamps Switch parameter is Active. If not Active Ignition OFF, disconnect the X2 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 10 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Test or replace the S48C multifunction switch 1 - instrument panel.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Instrument Panel Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Headlamp Switch Headlamps OFF SignalB257A 0011
Headlamp Switch Headlamps ON SignalB257A 0011
Headlamp Switch Park Lamps ON Signal2B257A 002
Turn Signal/Multifunction Switch Flash To Pass SignalB3806 0011
Turn Signal/Multifunction Switch High Beam SignalB3650 0811
Headlamp Switch Ground1
Turn Signal/Multifunction Switch Ground1
1. Headlamps Malfunction 2. Park, License, and/or Tail Lamps Malfunction

When the low beam headlamps are on and the turn signal/multifunction switch is placed in the high beam position, ground is applied to the body control module (BCM) through the high beam signal circuit. The BCM responds to the high beam request by applying ground to the high beam relay control circuit which energizes the high beam relay. With the high beam relay energized, the switch contacts close allowing battery voltage to flow through the high beam fuses to the high beam control circuits illuminating the high beam headlamps.

Battery voltage must be between 9-16 V.

The BCM detects a short to ground in the turn signal/multifunction switch high beam signal circuit.

The high beam headlamps will not operate.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S78 turn signal/multifunction switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 3 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool High Beam Select Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 2 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 2 and the ground circuit terminal 3.
  6. Verify the scan tool High Beam Select Switch parameter is Active. If not Active Ignition OFF, disconnect the X3 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 2 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Test or replace the S78 turn signal/multifunction switch.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Turn Signal Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/steering-column-switches/#steering-wheel-and-steering-column)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Headlamp Switch Headlamps OFF SignalB257A 0011
Headlamp Switch Headlamps ON SignalB257A 0011
Headlamp Switch Park Lamps ON Signal2B257A 002
Turn Signal/Multifunction Switch Flash To Pass SignalB3806 0011
Turn Signal/Multifunction Switch High Beam SignalB3650 0811
Headlamp Switch Ground1
Turn Signal/Multifunction Switch Ground1
1. Headlamps Malfunction 2. Park, License, and/or Tail Lamps Malfunction

When the turn signal/multifunction switch is momentarily placed in the flash to pass position, ground is applied to the body control module (BCM) through the flash to pass signal circuit. The BCM responds to the flash to pass request by applying ground to the high beam relay control circuit which energizes the high beam relay. With the high beam relay energized, the switch contacts close allowing battery voltage to flow through the high beam fuses to the high beam control circuits illuminating the high beam headlamps. The high beam headlamps will only illuminate for as long at the flash to pass switch is activated.

Battery voltage must be between 9-16 V.

The BCM detects a short to ground in the turn signal/multifunction switch flash to pass signal circuit.

The high beam lamps and the high beam indicator on the instrument panel cluster (IPC) are always ON.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S78 turn signal/multifunction switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 3 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Headlamps Flash Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 4 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the ground circuit terminal 3.
  6. Verify the scan tool Headlamps Flash Switch parameter is Active. If not Active Ignition OFF, disconnect the X3 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 4 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Test or replace the S78 turn signal/multifunction switch.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Turn Signal Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/steering-column-switches/#steering-wheel-and-steering-column)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Headlamp Switch Park Lamps ON Signal2B257A 002
License Plate Lamp ControlB3883 02B3883 01, B3883 04B3883 01
Park Lamps Control - LeftB2585 02B2585 04B2585 01, B2585 04
Park Lamps Control - RightB3867 02B3867 04B3867 01, B3867 04
Tail Lamps Control - LeftB3881 02B3881 04B3881 01
Tail Lamps Control - RightB3882 02B3882 04B3882 01
Headlamp Switch Ground2
License Plate Lamp Ground - Left1
License Plate Lamp Ground - Right1
Park Lamp Ground - Left Front1
Park Lamp Ground - Right Front1
Rear Tail/Stop Lamps Ground - Left1
Rear Tail/Stop Lamps Ground - Right1
Side Marker Lamp Ground - Left Front1
Side Marker Lamp Ground - Left Rear1
Side Marker Lamp Ground - Right Front1
Side Marker Lamp Ground - Right Rear1
1. Park, License, and/or Tail Lamps Malfunction 2. Park Lamp Switch Malfunction

When the headlamp switch is placed in the HEAD or PARK position, ground is applied to the park lamp switch ON signal circuit to the body control module (BCM). The BCM responds by applying voltage to the park lamps, tail lamps, and license lamps control circuits illuminating the park, tail, and license lamps.

  1. Battery voltage must be between 9-16 V.
  2. Park lamps ON.

DTC B3881 01

The BCM detects a short to voltage in the left rear tail lamp control circuit.

DTC B3881 02

The BCM detects a short to ground in the left rear tail lamp control circuit.

DTC B3881 04

The BCM detects an open/high resistance in the left rear tail lamp control circuit.

DTC B3882 01

The BCM detects a short to voltage in the right rear tail lamp control circuit.

DTC B3882 02

The BCM detects a short to ground in the right rear tail lamp control circuit.

DTC B3882 04

The BCM detects an open/high resistance in the right rear tail lamp control circuit.

The appropriate tail lamp will not operate.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

DTC B3881

  1. Ignition OFF, exterior lamps OFF, trunk latch latched, disconnect the harness connector at the appropriate E2L side marker lamp - left, E4N park/turn signal lamp - left front, or E5AA stop/tail lamp - left.
  2. Test for less than 10 ohms between the appropriate ground circuit terminal listed below and ground. E2LF side marker lamp - left front terminal 2 E2LR side marker lamp - left rear terminal B E4N park/turn signal lamp - left front terminal G E5AA tail/stop lamp - left terminal 1 If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON. E2LF side marker lamp - left front terminal 1 E2LR side marker lamp - left rear terminal A E4N park/turn signal lamp - left front terminal B E5AA tail/stop lamp - left terminal 3
  4. Verify the test lamp turns ON and OFF when commanding the Left Park Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate park lamp - left.

DTC B3882

  1. Ignition OFF, exterior lamps OFF, trunk latch latched, disconnect the harness connector at the appropriate or E2R side marker lamp - right, E4P park/turn signal lamp - right front, or E5AB stop/tail lamp - right.
  2. Test for less than 10 ohms between the appropriate ground circuit terminal listed below and ground. E2RF side marker lamp - right front terminal 2 E2RR side marker lamp - right rear terminal B E4P park/turn signal lamp - right front terminal G E5AB tail/stop lamp - right terminal 1 If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON. E2RF side marker lamp - right front terminal 1 E2RR side marker lamp - right rear terminal A E4P park/turn signal lamp - right front terminal B E5AB tail/stop lamp - right terminal 3
  4. Verify the test lamp turns ON and OFF when commanding the Right Park Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate park lamp - right.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Tail Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F8DA Fuse B+B3883 01, B3883 04B3883 01, B3883 04
License Plate Lamp ControlB3883 02B3883 01, B3883 04B3883 01
License Plate Lamp Ground - RightB3883 01, B3883 04
License Plate Lamp Ground - LeftB3883 01, B3883 04

When the headlamp switch is placed in the HEAD or PARK position, ground is applied to the park lamp switch ON signal circuit to the body control module (BCM). The BCM responds by applying voltage to the park lamps, tail lamps, and license lamps control circuits illuminating the park, tail, and license lamps.

Battery voltage must be between 9-16 V.

DTC B3883 01

Headlamp switch in OFF position.

DTC B3883 02 or B3883 04

Headlamp switch in PARK or ON positions.

DTC B3883 01

  1. The BCM detects a short to voltage in the license lamps control circuit.
  2. The BCM detects an open/high resistance in the license lamps ground circuit.
  3. The BCM detects a short to ground or an open/high resistance in the F8DA fuse B+ circuit.

DTC B3883 02

The BCM detects a short to ground in the license lamps control circuit.

DTC B3883 04

  1. The BCM detects an open/high resistance in the license lamps control circuit.
  2. The BCM detects an open/high resistance in the license lamps ground circuit.
  3. The BCM detects a short to ground or an open/high resistance in the F8DA fuse B+ circuit.

DTC B3883 01

License lamps always ON.

DTC B3883 02 or B3883 04

License lamps inoperative.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, disconnect the X2 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 1 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X2 harness connector at the K9 body control module.
  4. Ignition OFF, exterior lamps OFF, trunk latch latched, remove both E7 license plate lamp bulbs.
  5. Test for less than 5 ohms between each ground circuit terminal 2 and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  6. Connect a test lamp between the E7L license plate lamp - left control circuit terminal 1 and ground, ignition ON.
  7. Verify the test lamp turns ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  8. Ignition OFF.
  9. Connect a test lamp between the E7R license plate lamp - right control circuit terminal 1 and ground, ignition ON.
  10. Verify the test lamp turns ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If the test lamp turns ON and OFF
  11. Test or replace the appropriate E7 license plate lamp bulb.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Rear License Plate Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Center High Mounted Brake Lamp ControlB3884 0221
Center High Mounted Brake Lamp Ground2
1. Center High Mounted Brake Lamp Always ON 2. Center High Mounted Brake Lamp Always OFF

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal to the body control module (BCM). The BCM will apply battery voltage to the right, left and center stop lamp control circuits.

The brakes are applied.

The BCM detects a short to ground on the center high mounted brake lamp control circuit.

The center high mounted brake lamp will not illuminate.

  1. The DTC will be current for as long as the fault is present.
  2. When the fault is no longer present, the DTC will be a history DTC.
  3. A history DTC will clear after 50 ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, turn the center high mounted brake lamp ON and OFF by applying and releasing the brake pedal. The center high mounted brake lamp should turn ON and OFF when changing between the selected states.

  1. Ignition OFF, disconnect the harness connector at the E6 center high mounted stop lamp.
  2. Test for less than 30 ohms between the ground circuit terminal A and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal B and ground.
  4. Ignition ON, turn the center high mounted stop lamp ON and OFF by applying and releasing the brake pedal. The test lamp should turn ON and OFF when changing between the selected states. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  5. If all circuits test normal, replace the E6 center high mounted stop lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «High Mount Stop Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Turn Signal Switch Signal - Left111
Turn Signal Switch Signal - Right111
Turn Signal Control - Left FrontB3948 02B3948 04B3948 01, B3948 04
Turn Signal Control - Left RearB3950 02B3950 04B3950 01, B3950 04
Turn Signal Control - Right FrontB3949 02B3949 04B3949 01, B3949 04
Turn Signal Control - Right RearB3951 02B3951 04B3951 01, B3951 04
Turn Signal Lamp Ground - Left FrontB3948 01, B3948 04
Turn Signal Lamp Ground - Right FrontB3949 01, B3949 04
Turn Signal Lamp Ground - Left RearB3950 01, B3950 04
Turn Signal Lamp Ground - Right RearB3951 01, B3951 04
Turn Signal Repeater Lamp - Left GroundB3948 01, B3948 04
Turn Signal Repeater Lamp - Right GroundB3949 01, B3949 04
Turn Signal/Multifunction Switch Ground1
1. Turn Signal Lamps and/or Indicators Malfunction

Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START positions. When the turn signal/multifunction switch is placed in either the turn right or turn left position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM responds to the turn signal switch input by applying a pulsating voltage to the front and rear turn signal lamps through there respective control circuits. When a turn signal request is received by the BCM, a serial data message is sent to the instrument cluster requesting the respective turn signal indicator be pulsed ON and OFF.

Battery voltage must be between 9-16 V.

DTC B3948 01 and B3948 04

  1. The BCM detects an open/high resistance in the left front turn signal control circuit.
  2. The BCM detects an open/high resistance in the left front turn signal ground circuit.

DTC B3948 02

The BCM detects a short to ground in the left front turn signal control circuit.

DTC B3949 01 and B3949 04

  1. The BCM detects an open/high resistance in the right front turn signal control circuit.
  2. The BCM detects an open/high resistance in the right front turn signal ground circuit.

DTC B3949 02

The BCM detects a short to ground in the right front turn signal control circuit.

DTC B3948

  1. The left front turn signal is inoperative.
  2. The left turn signal indicator on the instrument cluster flashes rapidly.

DTC B3949

  1. The right front turn signal is inoperative.
  2. The right turn signal indicator on the instrument cluster flashes rapidly.
  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

DTC B3948

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate turn signal lamp - left.
  2. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground. E4N park/turn signal lamp - left terminal G A9A outside rearview mirror - driver terminal 4 - with GLD/GLL If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON. E4N park/turn signal lamp - left terminal A A9A outside rearview mirror - driver terminal 16 - with GLD/GLL
  4. Verify the test lamp turns ON and OFF when commanding the Left Front Turn Signal Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate turn signal lamp - left.

DTC B3949

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate turn signal lamp - right.
  2. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground. E4P park/turn signal lamp - right terminal G A9B outside rearview mirror - passenger terminal 4 - with GLD/GLL If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON. E4P park/turn signal lamp - right terminal A A9B outside rearview mirror - passenger terminal 16 - with GLD/GLL
  4. Verify the test lamp turns ON and OFF when commanding the Right Front Turn Signal Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate turn signal lamp - right.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Outside Rearview Mirror Replacement»(/buick/lacrosse/ii-2009-2013/remont/mirrors/#mirror-system)
  2. «Front Turn Signal Lamp Bulb Replacement (TT4)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F2DA (BCM 7) Fuse B+B3951 01, B3951 04B3951 01, B3951 04
F32UA (BCM 6) Fuse B+B3950 01, B3950 04B3950 01, B3950 04
Turn Signal Switch Signal - Left111
Turn Signal Switch Signal - Right111
Turn Signal Control - Left FrontB3948 02B3948 04B3948 01, B3948 04
Turn Signal Control - Left RearB3950 02B3950 04B3950 01, B3950 04
Turn Signal Control - Right FrontB3949 02B3949 04B3949 01, B3949 04
Turn Signal Control - Right RearB3951 02B3951 04B3951 01, B3951 04
Turn Signal Lamp Ground - Left FrontB3948 01, B3948 04
Turn Signal Lamp Ground - Right FrontB3949 01, B3949 04
Turn Signal Lamp Ground - Left RearB3950 01, B3950 04
Turn Signal Lamp Ground - Right RearB3951 01, B3951 04
Turn Signal Repeater Lamp - Left GroundB3948 01, B3948 04
Turn Signal Repeater Lamp - Right GroundB3949 01, B3949 04
Turn Signal/Multifunction Switch Ground1
1. Turn Signal Lamps and/or Indicators Malfunction

Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START positions. When the turn signal/multifunction switch is placed in either the turn right or turn left position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM responds to the turn signal switch input by applying a pulsating voltage to the front and rear turn signal lamps through there respective control circuits. When a turn signal request is received by the BCM, a serial data message is sent to the instrument cluster requesting the respective turn signal indicator be pulsed ON and OFF.

Battery voltage must be between 9-16 V.

DTC B3950 01 or B3950 04

  1. The BCM detects a short to ground or an open/high resistance in the F32UA (BCM 6) fuse B+ circuit.
  2. The BCM detects an open/high resistance in the left rear turn signal control circuit.
  3. The BCM detects an open/high resistance in the left rear turn signal ground circuit.

DTC B3950 02

The BCM detects a short to ground in the left rear turn signal control circuit.

DTC B3951 01 or B3951 04

  1. The BCM detects a short to ground or an open/high resistance in the F2DA (BCM 7) fuse B+ circuit.
  2. The BCM detects an open/high resistance in the right rear turn signal control circuit.
  3. The BCM detects an open/high resistance in the right rear turn signal ground circuit.

DTC B3951 02

The BCM detects a short to ground in the right rear turn signal control circuit.

DTC B3950

  1. The left rear turn signal is inoperative.
  2. The "Check Left Rear Turn Signal Lamp" message is displayed on the driver information center (DIC) display.
  3. The left turn signal indicator on the instrument cluster flashes rapidly.

DTC B3951

  1. The right rear turn signal is inoperative.
  2. The "Check Right Rear Turn Signal Lamp" message is displayed on the driver information center (DIC) display.
  3. The right turn signal indicator on the instrument cluster flashes rapidly.
  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

When testing at the rear turn signal lamp bulb socket, make sure all measurements and test lamp connections are in the correct terminal location and do not come in contact with each other during testing.

Schematic Reference

  1. «Exterior Lights Schematics»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-wiring-schematic-diagrams)
  2. «Body Control System Schematics»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#data-communications-system)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

DTC B3950

  1. Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 4 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X5 harness connector at the K9 body control module.
  4. Ignition OFF, exterior lamps OFF, remove the E4LR turn signal lamp bulb - left rear.
  5. Test for less than 5 ohms between the ground circuit terminal G and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  6. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  7. Verify the test lamp turns ON and OFF when commanding the Left Rear Turn Signal Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  8. Test or replace the E4LR turn signal lamp bulb - left rear.

DTC B3951

  1. Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 3 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X5 harness connector at the K9 body control module.
  4. Ignition OFF, exterior lamps OFF, remove the E4RR turn signal lamp bulb - right rear.
  5. Test for less than 5 ohms between the ground circuit terminal G and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  6. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  7. Verify the test lamp turns ON and OFF when commanding the Right Rear Turn Signal Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  8. Test or replace the E4RR turn signal lamp bulb - right rear.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Rear Turn Signal Lamp Bulb Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F8DA (BCM 1) Fuse B+C0890 03, U0121 00C0890 03, U0121 00
Brake Pedal Position Sensor 5 V ReferenceC0277 06, C0890 03, C0161 71C0277 06, C0161 71, C0161 5AC0277 07, C0890 07, C0161 71
Brake Pedal Position Sensor SignalC0277 06, U0140 71C0277 06, C0161 71, C0161 5AC0277 07, C0890 07, C0161 71C0277 09
Center High Mounted Stop Lamp Control222
Stop Lamp Control - Left111
Stop Lamp Control - Right111
Brake Pedal Position Sensor Low ReferenceC0277 07, C0161 71U0151 00, U0184 00
Center High Mounted Stop Lamp Ground2
Tail/Stop Lamp Ground - Left1
Tail/Stop Lamp Ground - Right1
1. Stop Lamps Malfunction 2. Center High Mounted Stop Lamp Malfunction

The brake pedal position (BPP) sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module provides a low reference signal and a 5 V reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the left and right stop lamp control circuits as well as the center high mounted stop lamp (CHMSL) control circuit illuminating the left and right stop lamps and the CHMSL.

  1. Battery voltage must be between 9-16 V.
  2. Brakes APPLIED.

DTC C0277 06

  1. The BCM detects a short to ground or an open/high resistance in the BPP sensor 5 V reference circuit.
  2. The BCM detects a short to ground or an open/high resistance in the BPP sensor signal circuit.

DTC C0277 07

  1. The BCM detects a short to voltage in the BPP sensor 5 V reference circuit.
  2. The BCM detects a short to voltage in the BPP sensor signal circuit.
  3. The BCM detects an open/high resistance in the BPP sensor low reference circuit.

DTC C0277 09

The BCM detects the BPP sensor signal is changing faster than possible under normal operating conditions.

DTC C0277 4B

The DTC will set when the BPP sensor home position is not learned.

DTC C0890 03

  1. The BCM detects a short to ground in the BPP sensor 5 V reference circuit.
  2. The BCM detects a short to ground or an open/high resistance in the F8DA (BCM 1) fuse B+ circuit.

DTC C0890 07

  1. The BCM detects a short to voltage in the BPP sensor 5 V reference circuit.
  2. The BCM detects a short to voltage in the BPP sensor low reference circuit.
  1. The Traction Control indicator is commanded ON.
  2. For DTC C0277 4B, the stop lamps may not activate at the expected brake pedal positions.
  1. The condition responsible for setting the DTC no longer exists.
  2. For DTC C0277 07 the ignition must be cycled before the code can be cleared.
  3. For DTC C0277 4B a successful brake pedal position sensor calibration has been performed.
  4. A history DTC will clear once 50 malfunction-free ignition cycles have occurred.
  5. A DTC will not clear the current status until the next ignition cycle.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

DTC C0277 or C0890

  1. Ignition OFF, disconnect the harness connector at the B22 brake pedal position sensor, ignition ON.
  2. Verify a test lamp illuminates between the low reference circuit terminal 1 and B+. If the test lamp does not illuminate Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp illuminates
  3. Ignition ON.
  4. Test for 4.8-5.2 V between the 5 V reference circuit terminal 2 and ground. If less than 4.8 V Ignition OFF, disconnect the X2 harness connector at the K9 body control module. Test for infinite resistance between the 5 V reference circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the 5 V reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If greater than 5.2 V Ignition OFF, disconnect the X2 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the 5 V reference circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If between 4.8-5.2 V
  5. Verify the scan tool Brake Pedal Applied parameter is Inactive. If not Inactive Ignition OFF, disconnect the X2 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 3 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If Active
  6. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the 5 V reference circuit terminal 2.
  7. Verify the scan tool Brake Pedal Applied parameter is Active. If not Active Ignition OFF, disconnect the X2 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 3 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  8. Test or replace the B22 brake pedal position sensor.

DTC C0277 4B

  1. Verify DTC C0277 4B is not set. If DTC C0277 4B is set Ignition ON Perform the BPP sensor recalibration procedure for the K9 body control module. Refer to «Brake Pedal Position Sensor Calibration»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions__brake-pedal-position-sensor-calibration) . Verify the DTC does not reset while operating the vehicle under the conditions for setting the DTC. If the DTC resets, replace the B22 brake pedal position sensor. If the DTC does not reset All OK. If DTC C0277 4B is not set
  2. All OK.

DTC C0277 09

  1. Verify DTC C0277 09 is not set. If DTC C0277 09 is set Replace the B22 brake pedal position sensor. Perform the BPP sensor recalibration procedure for the K9 body control module. Refer to «Brake Pedal Position Sensor Calibration»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions__brake-pedal-position-sensor-calibration) . Verify the DTC does not reset while operating the vehicle under the conditions for running the DTC. If the DTC resets, replace the K9 body control module. If the DTC does not reset All OK. If DTC C0277 09 is not set
  2. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Brake Pedal Position Sensor Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions__brake-pedal-position-sensor-replacement)
  2. «Brake Pedal Position Sensor Calibration»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions__brake-pedal-position-sensor-calibration)
  3. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Brake Applied SignalC0297 02C0297 021
1. Cruise Control Malfunction

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5 V reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the right and left stop lamp control circuits, engine control module (ECM), and center high mounted stop lamp control circuit.

  1. Battery voltage must be between 9-16 V.
  2. Brakes APPLIED.

The BCM detects a short to ground or an open/high resistance on the brake applied signal circuit.

The cruise control system is disabled.

  1. The condition responsible for setting the DTC no longer exists.
  2. A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Cruise Control Description and Operation»(/buick/lacrosse/ii-2009-2013/remont/cruise-control-systems/#cruise-control-system__cruise-control-description-and-operation)
  2. «Exterior Lighting Systems Description and Operation»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, disconnect the X1 harness connector at the K20 engine control module.
  2. Connect a test lamp between the signal circuit terminal 57 and ground, ignition ON.
  3. Verify the test lamp turns ON and OFF while pressing and releasing the brake pedal. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Replace the K20 engine control module.

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for BCM or ECM replacement, programming, and setup

Symptoms - Lighting

Note. The following steps must be completed before using a symptom table.

  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) before using a symptom table in order to verify that all of the following conditions are true: There are no DTCs set. The control modules can communicate via the serial data link.
  2. Review the system description and operation in order to familiarize yourself with the system functions. Refer to the following: «Exterior Lighting Systems Description and Operation»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-description-and-operation) «Interior Lighting Systems Description and Operation»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-description-and-operation)

Visual/Physical Inspection

  1. Inspect for aftermarket devices which could affect the operation of the lighting system. Refer to «Checking Aftermarket Accessories»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__checking-aftermarket-accessories) .
  2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Intermittent

Thoroughly inspect the wiring and connectors. An incomplete inspection of the wiring and connectors may result in misdiagnosis causing part replacement with the reappearance of the malfunction. If an intermittent malfunction exists, refer to Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

  1. «Adaptive Forward Lighting Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  2. «Backup Lamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  3. «Courtesy Lamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  4. «Daytime Running Lamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  5. «Door Sill Illumination Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  6. «Front Floor Console Cup Holder Illumination Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  7. «Front Fog Lamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  8. «Hazard Lamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  9. «Headlamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  10. «Headlamp Leveling Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  11. «High Intensity Discharge Lamp Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  12. «Interior Accent Lighting Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  13. «Interior Backlighting Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  14. «Park, License, and/or Tail Lamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  15. «Stop Lamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  16. «Turn Signal Lamps and/or Indicators Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures)
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Headlamp Control Module B+ (F64 UA)11
Headlamp Leveling Actuators B+ (F36 UA)11
Headlamp Control Module Ground1
Headlamp Leveling Actuator - Left Ground1
Headlamp Leveling Actuator - Right Ground1
1. Adaptive Forward Lighting Malfunction

Battery positive voltage is applied to the headlamp control module at all times. The headlamp control module has a normal operational voltage range of about 12.5-16 V and is only fully functional with the ignition switch is in the RUN position and the headlamp switch in the AUTOMATIC LIGHT position. The communications enable signal from the body control module (BCM) wakes the headlamp control module microprocessor. The headlamp control module receives serial data messages from the engine control module (ECM), transmission control module (TCM), electronic brake control module (EBCM), and BCM with information regarding power mode, speed, steering angle, transmission gear selection, and headlamp switch status. The headlamp control module calculates the headlamp angle and sends commands to the left and right adaptive forward lighting system headlamp actuators. The headlamp actuators drive the headlamps to the position commanded by the headlamp control module. The headlamp control module monitors the headlamp actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory and the driver will be notified with a message displayed over the driver information center located on the instrument cluster.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate M3 headlamp horizontal motor.
  2. Test for less than 5 ohms between the ground circuit terminal 2 and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminal 1 and ground. If the test lamp does not illuminate Ignition OFF, disconnect the X1 harness connector at the X50A fuse block - underhood. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the X50A fuse block - underhood. If the test lamp illuminates
  5. Test or replace the K26 headlamp control module.
  6. Ignition ON.
  7. Verify the appropriate headlamp operates to the LEFT and RIGHT positions when commanding the appropriate Headlamp Horizontal Motor control LEFT and RIGHT with a scan tool. If the appropriate headlamp does not operate LEFT and RIGHT, test or replace the appropriate headlamp assembly.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Headlamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for headlamp control module replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F32UA Fuse B+B2545 01, B2545 04, B3950 01, B3950 04B2545 01, B2545 04, B3950 01, B3950 04
Backup Lamps ControlB2545 02B2545 04B2545 01
Backup Lamp Ground - Left1
Backup Lamp Ground - Right1
1. Backup Lamps Malfunction

With the engine running and the transmission in the reverse position, the transmission control module (TCM) sends a serial data message to the body control module (BCM). The message indicates that the gear selector is in the reverse position. The BCM applies battery voltage to the backup lamps control circuit illuminating the backup lamps. Once the driver moves the gear selector out of the reverse position, a message is sent by the TCM via serial data requesting the BCM to remove battery voltage from the backup lamps control circuit. The engine must be running for the backup lamps to operate.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 4 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Ignition OFF, connect the X5 harness connector at the K9 body control module.
  4. Ignition OFF, exterior lamps OFF, trunk latch latched, remove the appropriate E5 backup lamp bulb at the appropriate E5 tail lamp assembly.
  5. Test for less than 5 ohms between the ground circuit terminal B and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  6. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  7. Verify the test lamp turns ON and OFF when commanding the Backup Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  8. Test or replace the appropriate E5 backup lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Backup Lamp Bulb Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Courtesy Lamps Control - Terminal 2 X7B1480 0211
Dome Lamps ControlB2615 0222
Center Compartment Lamp Switch Ground1
Dome/Reading Lamps - Front Ground1, 2
Dome/Reading Lamps - 2nd Row Ground1, 2
Instrument Panel Compartment Lamp Ground1
Sunshade Mirror Lamp - Left Ground1
Sunshade Mirror Lamp - Right Ground1
1. Courtesy Lamps Malfunction 2. Dome Lamps Malfunction

The body control module (BCM) supplies battery voltage to the front and rear reading lamps, left and right sunshade lamps, center console compartment lamp, and instrument panel compartment lamp via the courtesy lamp control circuit. When the instrument panel compartment or a sunshade mirror is opened, the switch contacts close allowing battery voltage to flow illuminating the respective lamps. The front and rear reading lamps are controlled by individual switches that are activated by the operator when additional cabin lighting is required. In the event that any of these courtesy lamps were to remain illuminated for more than 10 minutes with the ignition switch in the OFF position and no doors opened, the BCM will deactivate the courtesy lamp control circuit to prevent total battery discharge.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the inoperative courtesy lamp. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground. E37F dome/reading lamps - front terminal 6 E37B dome/reading lamps - rear terminal 6 E31L sunshade mirror lamp - left terminal B E31R sunshade mirror lamp - right terminal B E27 instrument panel compartment lamp terminal 2 S5 center console compartment lamp switch terminal 2 If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground. E37F dome/reading lamps - front terminal 1 E37B dome/reading lamps - rear terminal 1 E31L sunshade mirror lamp - left terminal A E31R sunshade mirror lamp - right terminal A E27 instrument panel compartment lamp terminal 1 S5 center console compartment lamp switch terminal 1
  4. Verify the test lamp turns ON and OFF when commanding the Inadvertent Load ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate courtesy lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Sunshade Replacement»(/buick/lacrosse/ii-2009-2013/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling)
  2. «Instrument Panel Compartment Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Sunshade Illuminated Mirror Lamp Bulb Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Front Floor Console Armrest Compartment Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Dome and Reading Lamp Replacement - Front»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  6. «Dome and Reading Lamp Replacement - Rear»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  7. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F9DA Fuse B+11
F23DA Fuse B+11
Ambient Light Sensor SignalB2645 03B2645 07B2645 07
Daytime Running Lamp Control - Left (T4F)B2600 02B2600 04B2600 01
Daytime Running Lamp Control - Right (T4F)B2605 02B2605 04B2605 01
Ambient Light Sensor Low ReferenceB2645 071
Daytime Running Lamp Ground - Left (T4F)1
Daytime Running Lamp Ground - Right (T4F)1
1. Daytime Running Lamps Malfunction

The ambient light sensor is used to monitor outside lighting conditions. The body control module (BCM) provides a 5-volt reference signal to the ambient light sensor. Depending on outside lighting conditions, the ambient light sensor provides a voltage signal to the BCM that will vary between 0.2 and 4.9 volts. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic headlamp system control when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying voltage to the DRL control circuits illuminating the DRLs. Any function or condition that turns on the headlamps will cancel DRL operation.

Schematic Reference

  1. «Headlights/Daytime Running Lights (DRL) Schematics»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-wiring-schematic-diagrams)
  2. «Body Control System Schematics»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#data-communications-system)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify the left daytime running lamp turns ON and OFF while commanding the Left Dedicated Daytime Running Lamp ON and OFF with a scan tool. If the left daytime running lamp does not turn ON and OFF Refer to Daytime Running Lamps Malfunction below. If the left daytime running lamp turns ON and OFF
  3. Verify the right daytime running lamp turns ON and OFF while commanding the Right Dedicated Daytime Running Lamp ON and OFF with a scan tool. If the right daytime running lamp does not turn ON and OFF Refer to Daytime Running Lamps Malfunction below. If the right daytime running lamp turns ON and OFF
  4. Refer to Ambient Light Sensor Malfunction below.

Daytime Running Lamps Malfunction

  1. Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON.
  2. Verify a test lamp illuminates between the B+ circuit terminal 2 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  3. Verify a test lamp illuminates between the B+ circuit terminal 3 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp illuminates
  4. Ignition OFF, connect the X1 harness connector at the K9 body control module.
  5. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E4 daytime running lamp.
  6. Test for less than 5 ohms between the ground circuit terminal G and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  7. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  8. Verify the test lamp turns ON and OFF when commanding the appropriate Dedicated Daytime Running Lamp Command ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  9. Test or replace the appropriate E4 daytime running lamp.

Ambient Light Sensor Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, open and close drivers door, disconnect the harness connector at the B10B ambient light/sunload sensor. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the low reference circuit terminal 6 and ground. If 15 ohms or greater Ignition OFF, disconnect the X2 harness connector at the K33 HVAC control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K33 HVAC control module. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Ambient Light Sensor parameter is greater than 4.65 V. If 4.65 V or less Ignition OFF, disconnect the X2 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 5 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If greater than 4.65 V
  5. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the low reference circuit terminal 6.
  6. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 V. If 0.196 V or greater Ignition OFF, disconnect the X2 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 5 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If less than 0.196 V
  7. Test or replace the B10B ambient light/sunload sensor.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Daytime Running Lamp Bulb Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Sun Load Temperature and Headlamp Automatic Control Ambient Light Sensor Replacement»(/buick/lacrosse/ii-2009-2013/remont/automatic-hvac-system/#hvac-system-automatic)
  3. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or HVAC control module replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
ControlB2615 0221
Ground2
1. Door Sill illumination Always ON 2. Door Sill illumination Inoperative

When the BCM receives a signal to command the courtesy lamps ON, it applies battery voltage through the dome/courtesy lamps control circuit to the courtesy lamps. The door sill illumination receives voltage through the courtesy lamps circuit. The door sill illumination harness connector includes a power inverter which converts the battery voltage to 150 V AC (550 Hz). This AC voltage is supplied to the door sill lamps and causes them to illuminate.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Observe the vehicle entry courtesy lamps while opening and closing the driver door. The entry courtesy lamps should turn ON the door is opened and OFF when the door is closed. If the entry courtesy lamps do not change between the selected states, refer to «Courtesy Lamps Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures) .
  2. Observe the door sill plate lamps while opening and closing the driver door. The door sill plate lamps should turn ON when the door is opened and turn OFF when the door is closed. If a single door sill plate lamp does not change between the selected states, replace the appropriate door sill plate lamp component. If all of the door sill plate lamps do not change between the selected states, refer to Circuit/System Testing below.
WARNINGDC and AC high-voltage is present. To reduce the risk of severe shocks and burns, the high-voltage system should be disabled any time service work is being performed on or around the high-voltage system. When in doubt, always disable the high-voltage system. The 12-volt system will still be active after the high-voltage system has been disabled.
  1. Ignition OFF, verify door sill plate lamp ground circuit 1150 is securely connected to the driver side kick panel ground stud. If the door sill plate lamp ground circuit is not securely connected, repair the poor connection.
  2. Disconnect the X2 (blue) harness connector at the BCM.
  3. Using the appropriate test tool, connect a test lamp between the control circuit terminal 5 at the BCM and ground.
  4. Ignition ON, turn the door sill plate lamp ON and OFF by opening and closing the vehicle door. The test lamp should turn ON and OFF when changing between the selected states. If the test lamp is always ON or OFF, replace the BCM.
  5. If all circuits test normal, replace the door sill plate lamp kit.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. Front and Rear Side Door Sill Trim Plate Kit Installation
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Exterior Courtesy Lamps ControlB263A 02B263A 041
Outside Rearview Mirror - Driver Ground1
Outside Rearview Mirror - Passenger Ground1
1. Exterior Courtesy Lamps Malfunction

The body control module (BCM) supplies battery voltage to the exterior courtesy LED lighting located under each outside rearview mirror for approach lighting. When the keyless entry transmitter is operated to the lock/unlock functions the exterior door handles LED and the LED lighting located under each outside rearview mirror for approach lighting are commanded ON.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition OFF, all doors closed, all accessories OFF, disconnect the harness connectors at the inoperative A9 outside rearview. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the appropriate ground circuit terminal 4 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Connect a test lamp between the control circuit terminal 17 and ground.
  4. Verify the test lamp turns ON and OFF when commanding the Outside Rear View Mirror Courtesy Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X7 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X7 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate door courtesy lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Outside Rearview Mirror Replacement»(/buick/lacrosse/ii-2009-2013/remont/mirrors/#mirror-system)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Front Fog Lamp and I/P Dimmer Switch B+B1405 03, B1529 03, B257B 03B257B 03
Front Fog Lamp and I/P Dimmer Switch SignalB257B 03B257B 031
Front Fog Lamp Relay ControlB2530 02, B2530 04B2530 02, B2530 04B2530 01
Front Fog Lamp Control111
Front Fog Lamp Ground - Left1
Front Fog Lamp Ground - Right1
1. Front Fog Lamps Malfunction

The front fog lamp switch is an input to the body control module (BCM) and is contained in the headlamp switch assembly. The BCM supplies voltage to the front fog lamp switch via the front fog lamp and instrument panel dimmer switch B+ circuit. When the front fog lamp switch is pressed, voltage from the B+ circuit is pulled down through the front fog lamp switch resistor. The front fog lamp resistor is part of the resistor ladder that also provides the dimming signals for the instrument panel dimmer switches. The BCM receives the voltage signal through the front fog lamp and I/P dimmer switch signal circuit.

The front fog lamp relay is supplied with battery voltage at all times. The front fog lamp switch signal circuit is grounded momentarily by pressing the front fog lamp switch. The body control module (BCM) energizes the front fog lamp relay by applying ground to the front fog lamp relay control circuit. When the front fog lamp relay is energized, the relay switch contacts close and battery voltage is applied through the FRT FOG fuse to the front fog lamp control circuit which illuminates the front fog lamps.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, headlamps ON.
  2. Verify the scan tool Front Fog Lamps Switch parameter changes between Active and Inactive while commanding the front fog lamps ON and OFF with the front fog lamp switch. If the parameter does not change Refer to Front Fog Lamp Switch Malfunction below. If the parameter changes
  3. Verify the front fog lamps turn ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool. If the front fog lamps do not turn ON and OFF Refer to Front Fog Lamps Malfunction below. If the front fog lamps turn ON and OFF
  4. Verify the front fog lamp indicator on the instrument cluster turns ON and OFF while commanding the front fog lamps ON and OFF with the front fog lamp switch. If the front fog lamp indicator does not turn ON and OFF Refer to Front Fog Lamp Indicator Malfunction below. If the front fog lamp indicator turns ON and OFF
  5. All OK.

Front Fog Lamp Switch Malfunction

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the S30 headlamp switch, ignition ON.
  2. Test for B+ between the B+ circuit terminal 1 and ground. If less than B+ Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If B+
  3. Verify the scan tool LED Backlight Dimming Command parameter is greater than 40%. If 40% or less Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 12 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If greater than 40%
  4. Install a 3 A fused jumper wire between the signal circuit terminal 12 and the B+ circuit terminal 1.
  5. Verify the scan tool LED Backlight Dimming Command parameter is less than 30%. If 30% or greater Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If less than 30%
  6. Test or replace the S30 headlamp switch.

Front Fog Lamps Malfunction

  1. Ignition OFF, disconnect the X2 harness connector at the X50A fuse block - underhood.
  2. Connect a test lamp between the control circuit terminal 19 and B+, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the control circuit terminal and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Ignition OFF, connect the X2 harness connector at the X50A fuse block - underhood.
  5. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E29 fog lamp.
  6. Test for less than 5 ohms between the ground circuit terminal B and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  7. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  8. Verify the test lamp turns ON and OFF when commanding the Front Fog Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X1 harness connector at the X50A fuse block - underhood. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the X50A fuse block - underhood. If the test lamp is always ON Ignition OFF, disconnect the X1 harness connector at the X50A fuse block - underhood, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the X50A fuse block - underhood. If the test lamp turns ON and OFF
  9. Test or replace the appropriate E29 fog lamp.

Front Fog Lamp Indicator Malfunction

  1. Ignition ON.
  2. Verify the front fog lamp indicator turns ON and OFF when commanding the Instrument Cluster All Indicators Test ON and OFF with a scan tool. If the front fog lamp indicator is always OFF or remains ON Replace the P16 instrument cluster. If the front fog lamp indicator turns ON and OFF
  3. Replace the K9 body control module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Headlamp Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Front Fog Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Front Fog Lamp Bulb Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Relay Replacement (Within an Electrical Center)»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  5. «Fuse Block Replacement»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  6. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or instrument cluster replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The front floor console cup holder lighting unit consists of a lighting electronic control unit, membrane control switch, cupholder LEDs and footwell LEDs. When the driver activates the control switch, the control unit receives a signal to command the accessory lighting ON. This signal applies the appropriate voltage to each of the three signal circuits on the footwell LED and cup holder LED harnesses. Power for the accessory lighting is taken from the accessory power outlet - center console compartment.

When the lighting unit is initially installed and powered up, the LEDs should be OFF. The ECU allows for six different colors of light to be displayed. Touching the membrane switch once will command the ECU on, and the LEDs will illuminate blue. Subsequent control of the membrane switch will go through the full color progression: blue - red - white - yellow - purple - green. Activating the switch a seventh time will turn the lighting off, where the full progression can be cycled through again. If the accessory lighting LEDs are running when the vehicle is turned OFF, the LEDs will default to illuminate blue once the vehicle is turned on again.

The lighting control unit includes a two amp fuse, and also has a battery power harness - which is permanently attached. A connector for the membrane switch will plug into the control unit, as will separate connectors for the footwell lighting (gray connector) and cup holder lighting (white connector).

The following two tables can be used to try and troubleshoot incorrect operation of the footwell and cup holder LEDs. The tables show the voltage measurements taken at each pin for each of the 7 controller output combinations (6 different colors and 1 off position). The table labeled gray connector refers to the footwell lighting outputs and the table labeled white connector refers to the cup holder lighting outputs. Measurements are taken from the appropriate colored electrical control unit connector at the terminal position indicated (red, green, blue).

Controller OutputRed Terminal VoltageGreen Terminal VoltageBlue Terminal Voltage
Position 0 = Off0 V0 V0 V
Position 1 = Blue0 V1.57 V12.37 V
Position 2 = Red8.4 V0 V0 V
Position 3 = White6.5 V9.73 V12.19 V
Position 4 = Yellow8.42 V3.68 V0 V
Position 5 = Purple3.35 V0 V10.46 V
Position 6 = Green0.008 V12.34 V4.78 V

Gray Connector

Controller OutputRed Terminal VoltageGreen Terminal VoltageBlue Terminal Voltage
Position 0 = Off0 V0 V0 V
Position 1 = Blue0 V0.292 V12.5 V
Position 2 = Red12.31 V0 V0 V
Position 3 = White10.13 V3.73 V12.3 V
Position 4 = Yellow12.27 V1.21 V0 V
Position 5 = Purple5.65 V0 V10.63 V
Position 6 = Green0 V5 V4.8 V

White Connector

The resistance to ground was also measured for the gray and white terminals. While the ignition for the vehicle was off, the resistance was 15.1 ohms. The resistance was 22 ohms while the key was off.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, install a 12 V DC accessory into the X80B accessory power receptacle - center console 2. Command the Accessory/Retained Accessory Power Relay Command ON and OFF with a scan tool. The KR80 accessory relay should click and the 12 V DC accessory should have power. If the 12 V DC accessory does not have power, refer to «Power Outlet Receptacle Malfunction (110V AC)»(/buick/lacrosse/ii-2009-2013/remont/body-electrical/#power-outlets) , «Power Outlet Receptacle Malfunction (12V DC)»(/buick/lacrosse/ii-2009-2013/remont/body-electrical/#power-outlets) .
  2. Ignition ON, observe the front floor console lights and cup holder lights while activating the membrane switch. The lighting should turn cycle through its color progression as the switch is activated. If the footwell lights and cup holder lights do not cycle through the color progression as the switch is activated, refer to Component Testing below.
  3. Observe the cup holder lights while activating the membrane switch. The lighting should turn cycle through its color progression as the switch is activated. If the cup holder lights do not cycle through the color progression as the switch is activated, refer to Cup Holder Lighting Malfunction below.
  4. Observe the front footwell lights while turning the accessory lighting electronic control unit switch ON and OFF. The lighting should turn ON and OFF when changing between the selected states. If the footwell lights do not cycle through the color progression as the switch is activated, refer to Front Footwell Lighting Malfunction below.

Cup Holder Lighting Malfunction

  1. Ignition OFF, disconnect the electronic control unit harness connector at the X80B accessory power receptacle - center console 2.
  2. Test for less than 5 ohms between the ground circuit terminal C and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the control circuit terminal A and ground. If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal and the control circuit fuse is open, test the signal circuit terminal A for a short to ground.
  4. Ignition OFF, connect the electronic control unit harness connector at the X80B accessory power receptacle - center console 2. Disconnect the cup holder lighting harness connector at electronic control unit.
  5. Test for less than 5 ohms between the ground circuit terminal 4 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  6. Connect a test lamp between the control circuit terminal 1 and the ground circuit terminal 4.
  7. Cycle through the output color combinations by using the membrane switch. The test lamp should turn ON and OFF depending on the voltage setting of the lighting combination. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the electronic control unit. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the electronic control unit.
  8. Connect a test lamp between the control circuit terminal 2 and the ground circuit terminal 4.
  9. Cycle through the output color combinations by using the membrane switch. The test lamp should turn ON and OFF depending on the voltage setting of the lighting combination. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the electronic control unit. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the electronic control unit.
  10. Connect a test lamp between the control circuit terminal 3 and the ground circuit terminal 4.
  11. Cycle through the output color combinations by using the membrane switch. The test lamp should turn ON and OFF depending on the voltage setting of the lighting combination. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the electronic control unit. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the electronic control unit.
  12. If all circuits test normal, test or replace the cup holder lighting.

Front Footwell Lighting Malfunction

  1. Ignition OFF, disconnect the electronic control unit harness connector at the X80B accessory power receptacle - center console 2.
  2. Test for less than 5 ohms between the ground circuit terminal C and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the control circuit terminal A and ground. If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal and the control circuit fuse is open, test the signal circuit terminal A for a short to ground.
  4. Ignition OFF, connect the electronic control unit harness connector at the X80B accessory power receptacle - center console 2. Disconnect the cup holder lighting harness connector at electronic control unit.
  5. Test for less than 5 ohms between the ground circuit terminal 4 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  6. Connect a test lamp between the control circuit terminal 1 and the ground circuit terminal 4.
  7. Cycle through the output color combinations by using the membrane switch. The test lamp should turn ON and OFF depending on the voltage setting of the lighting combination. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the electronic control unit. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the electronic control unit.
  8. Connect a test lamp between the control circuit terminal 2 and the ground circuit terminal 4.
  9. Cycle through the output color combinations by using the membrane switch. The test lamp should turn ON and OFF depending on the voltage setting of the lighting combination. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the electronic control unit. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the electronic control unit.
  10. Connect a test lamp between the control circuit terminal 3 and the ground circuit terminal 4.
  11. Cycle through the output color combinations by using the membrane switch. The test lamp should turn ON and OFF depending on the voltage setting of the lighting combination. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the electronic control unit. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the electronic control unit.
  12. If all circuits test normal, test or replace the footwell lighting.

Component Testing

  1. Ignition OFF, disconnect the membrane switch harness connector at the electronic control unit.
  2. Test for infinite resistance between the signal terminal 4 and the ground terminal 7 with the switch in the open position. If not the specified value, replace the membrane switch.
  3. Test for less than 5 ohms between the signal terminal 4 and the ground terminal 7 with the switch in the closed position. If greater than the specified range, replace the membrane switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Repair Verification

  1. Front Floor Console Cup Holder Illumination Lamp Package Installation
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for module replacement, programming and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Hazard Warning Switch Signal111B3596 00
Hazard Warning Switch LED Backlighting Control222
Hazard Warning Switch Ground1
1. Hazard Lamps Malfunction 2. Hazard Warning Switch Backlighting Malfunction

The hazard flashers may be activated in any power mode. The hazard warning switch signal circuit is momentarily grounded when the hazard warning switch is pressed. The body control module (BCM) responds to the hazard warning switch signal input by supplying battery voltage to all four turn signal lamps in an ON and OFF duty cycle. When the hazard warning switch is activated, the BCM sends a serial data message to the instrument cluster requesting both turn signal indicators to be cycled ON and OFF.

The instrument panel dimmer switch controls are located on the headlamp switch assembly and are used to increase and decrease the brightness of the interior backlighting components. When the instrument panel dimmer switch is placed in a desired brightness position, the body control module (BCM) receives a signal from the instrument panel dimmer switch and responds by applying a pulse width modulated (PWM) voltage to the hazard warning switch LED backlighting control circuit illuminating the LED to the desired level of brightness.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify the scan tool Hazard Lamps Switch parameter changes between Active and Inactive while commanding the hazard lamps ON and OFF with the hazard warning switch. If the parameter does not change Refer to Hazard Warning Switch Malfunction below. If the parameter changes
  3. Verify all left and right turn signal lamps turn ON and OFF while commanding the hazard lamps ON and OFF with the hazard warning switch. If all turn signal lamps do not turn ON and OFF Refer to «Turn Signal Lamps and/or Indicators Malfunction»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-diagnostic-information-and-procedures) If all turn signal lamps turn ON and OFF
  4. Verify the hazard warning switch backlighting turns ON and OFF while commanding the Hazard Lamps Switch Backlight ON and OFF with a scan tool. If the hazard warning switch backlighting does not turn ON and OFF Refer to Hazard Warning Switch Backlighting Malfunction below. If the hazard warning switch backlighting turns ON and OFF
  5. All OK.

Hazard Warning Switch Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S48C multifunction switch 1 - instrument panel. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 7 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Hazard Lamps Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X2 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 10 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 10 and ground.
  6. Verify the scan tool Hazard Lamps Switch parameter is Active. If not Active Ignition OFF, disconnect the X2 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 10 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Test or replace the S48C multifunction switch 1 - instrument panel.

Hazard Warning Switch Backlighting Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S48C multifunction switch 1 - instrument panel. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 7 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Connect a test lamp between the control circuit terminal 5 and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the Hazard Lamps Switch Backlight ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the S48C multifunction switch 1 - instrument panel.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Instrument Panel Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Left Headlamp Low Beam Supply VoltageB257C 00B257C 00B257C 00
Right Headlamp Low Beam Supply VoltageB257D 00B257D 00B257D 00
Headlamp High Beam Relay ControlB2580 0211
Headlamp Low Beam Relay Control222
Left Headlamp Low Beam GroundB257C 00
Right Headlamp Low Beam GroundB257D 00
1. High Beam Headlamp Malfunction 2. Low Beam Headlamp Malfunction

The vehicle headlamps are controlled by the body control module (BCM) based on inputs from the headlamp switch and the turn signal/multifunction switch. The headlamp switch has four positions: OFF, AUTOMATIC LIGHT, PARKING LIGHT, and LOW BEAM. The default headlamp switch position is AUTOMATIC LIGHT, in which the BCM uses the ambient light sensor to determine when headlamps are needed. The OFF portion of the headlamp switch is a momentary switch which overrides the automatic headlamp and will turn OFF the vehicle headlamps. When in the OFF position, the headlamp switch grounds the headlamp switch headlamps OFF signal circuit, prompting the BCM to turn OFF the headlamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The LOW BEAM position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the LOW BEAM position, the headlamp switch headlamps on signal circuit is grounded, prompting the BCM to turn on the headlamps, regardless of other factors such as ambient light.

When a low beam request is received, the BCM grounds the headlamp low beam relay control circuit. This energizes the coil in the headlamp low beam relay, causing the relay switch to close. This then applies B+ to both low beam high intensity discharge (HID) headlamps through the left low beam and right low beam fuses, illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit. This energizes the coil in the high beam relay, causing the relay switch to close. This then applies B+ to both low beam HID headlamps through the left high beam and right high beam fuses, illuminating the high beam headlamps.

The following symptoms are noticeable signs of bulb failure

  1. Flickering light, caused in the early stages of bulb failure.
  2. Lights go out, caused when the ballast detects excessive, repetitive bulb re-strike.
  3. Color change-The lamp may change to a dim pink glow.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, observe the function of the low beam headlamps while commanding the Low Beam Lamps ON and OFF with a scan tool. The E4G headlamp-left low beam and the E4H headlamp-right low beam should turn ON and OFF while changing between the commanded states. If the E4G headlamp-left low beam is always OFF, refer to Left Low Beam Inoperative below. If the E4H headlamp-right low beam is always OFF, refer to Right Low Beam Inoperative below. If both low beam headlamps are always ON or always OFF, refer to Low Beam Command Malfunction below.
  2. Ignition ON, observe the function of the high beam headlamps while commanding the High Beam Lamps ON and OFF with a scan tool. The E4E headlamp-left high beam and the E4F headlamp-right high beam should turn ON and OFF while changing between the commanded states. If the E4E headlamp-left high beam is always OFF, refer to Left High Beam Inoperative below. If the E4F headlamp-right high beam is always OFF, refer to Right High Beam Inoperative below. If both high beam headlamps are always ON or always OFF, refer to High Beam Command Malfunction below.
WARNINGThe high intensity discharge system produces high voltage and current. To reduce the risk of severe shocks and burns: Never open the high intensity discharge system ballast or the arc tube assembly starter. Never probe between the high intensity discharge system ballast output connector and the arc tube assembly.

Left Low Beam Inoperative

  1. Ignition OFF, disconnect the X118 inline harness connector at the E13L headlamp-left.
  2. Test for less than 30 ohms between the ground circuit harness connector terminal G and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal A and ground.
  4. Ignition ON, command the Low Beam Lamps ON with a scan tool, the test should illuminate while commanding the headlamp ON. If the test lamp does not illuminate and the circuit fuse is good, test the control circuit for an open/high resistance. If the test lamp does not illuminate and the circuit fuse is open, test the control circit for a short to ground.
  5. If all circuits test normal, replace the E4G headlamp-left low beam.

Right Low Beam Inoperative

  1. Ignition OFF, disconnect the X120 inline harness connector at the E13R headlamp-right.
  2. Test for less than 30 ohms between the ground circuit harness connector terminal G and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal A and ground.
  4. Ignition ON, command the Low Beam Lamps ON with a scan tool, the test should illuminate while commanding the headlamp ON. If the test lamp does not illuminate and the circuit fuse is good, test the control circuit for an open/high resistance. If the test lamp does not illuminate and the circuit fuse is open, test the control circit for a short to ground.
  5. If all circuits test normal, replace the E4H headlamp-right low beam.

Low Beam Command Malfunction

  1. Ignition OFF, disconnect the KR49 headlamp low beam relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground. If the test lamp illuminates, test the control circuit for a short to voltage
  3. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistanc.e
  4. Verify that a test lamp illuminates between the B+ circuit terminal 86 and ground. If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  5. Connect a 15A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the E4G headlamp-left low beam and the E4H headlamp-right low beam are activated. If the E4G headlamp-left low beam and the E4H headlamp-right low beam do not activate, test the control circuit for a short to ground or an open/high resistance.
  6. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
  7. Ignition ON, command the Low Beam Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 BCM. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.
  8. If all circuits test normal, test or replace the KR49 headlamp low beam relay.

Left High Beam Inoperative

  1. Ignition OFF, disconnect the X118 inline harness connector at the E13L headlamp-left.
  2. Test for less than 30 ohms between the ground circuit harness connector terminal J and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal D and ground.
  4. Ignition ON, command the High Beam Lamps ON with a scan tool, the test should illuminate while commanding the headlamp ON. If the test lamp does not illuminate and the circuit fuse is good, test the control circuit for an open/high resistance. If the test lamp does not illuminate and the circuit fuse is open, test the control circit for a short to ground.
  5. If all circuits test normal, replace the E4E headlamp-left high beam.

Right High Beam Inoperative

  1. Ignition OFF, disconnect the X120 inline harness connector at the E13R headlamp-right.
  2. Test for less than 30 ohms between the ground circuit harness connector terminal J and ground. If greater than the specified value, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal D and ground.
  4. Ignition ON, command the High Beam Lamps ON with a scan tool, the test should illuminate while commanding the headlamp ON. If the test lamp does not illuminate and the circuit fuse is good, test the control circuit for an open/high resistance. If the test lamp does not illuminate and the circuit fuse is open, test the control circit for a short to ground.
  5. If all circuits test normal, replace the E4F headlamp-right high beam.

High Beam Command Malfunction

  1. Ignition OFF, disconnect the X1 harness connector at the X50A underhood fuse block.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal listed below and ground. Control terminal 13 Control terminal 14
  3. If the test lamp is ON, test the control circuit for a short to voltage.
  4. Ignition OFF, connect the X1 harness connector and disconnect the X2 harness connector at the X50A underhood fuse block.
  5. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 58 and ground. If the test lamp is ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM
  6. Connect a test lamp between the control circuit terminal 58 and B+.
  7. Ignition ON, command the High Beam Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit tests normal, replace the K9 BCM. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 BCM
  8. If all circuits test normal, replace the X50A underhood fuse block.

Relay Test

  1. Ignition OFF, disconnect the KR49 headlamp low beam relay.
  2. Test for 60-180 ohms between terminals 85 and 86. If not within the specified range, replace the KR49 headlamp low beam relay.
  3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the KR49 headlamp low beam relay.
  4. Install a 15A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the KR49 headlamp low beam relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Relay Replacement (Within an Electrical Center)»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Fuse Block Replacement»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  3. «Headlamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Headlamp Ballast Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F9DA (BCM 4) Fuse B+B2699 01, B2699 04B2699 01, B2699 04
F23DA (BCM 3) Fuse B+B2575 01, B2575 04B2575 01, B2575 04
Headlamp Switch Headlamps OFF SignalB257A 0033
Headlamp Switch Headlamps ON SignalB257A 0033
Headlamp Switch Park Lamps ON Signal3B257A 003
Turn Signal/Multifunction Switch Flash To Pass SignalB3806 0044
Turn Signal/Multifunction Switch High Beam SignalB3650 0844
Headlamp Low Beam Relay ControlB258A 02, B258A 04B258A 02, B258A 04B258A 01
Headlamp High Beam Relay ControlB2580 02, B2580 04B2580 02, B2580 04B2580 01
Low Beam Headlamp Control - Left (T4A)B2575 02B2575 01, B2575 041
Low Beam Headlamp Control - Right (T4A)B2699 02B2699 01, B2699 041
Low Beam Headlamp Control - Left (T4F)111
Low Beam Headlamp Control - Right (T4F)111
High Beam Headlamp Control - Left222
High Beam Headlamp Control - Right222
Headlamp Ground - Left1
Headlamp Ground - Right1
Headlamp Switch Ground3
Turn Signal/Multifunction Switch Ground4
1. Headlamps Malfunction - Low Beam 2. Headlamps Malfunction - High Beam 3. Headlamp Switch Malfunction 4. Turn Signal/Multifunction Switch Malfunction

Low Beams - with T4A

The body control module (BCM) monitors three signal circuits from the headlamp switch. When the headlamp switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor to determine if headlamps are required or if daytime running lamps will be activated based on outside lighting conditions. When the headlamp switch is placed in the OFF position, the headlamp switch headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the headlamp switch in the PARK position, the headlamp switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the headlamp switch is placed in the HEADLAMP position, both the headlamp switch park lamps ON signal circuit and the headlamp switch headlamps ON signal circuit are grounded. The BCM responds to the inputs by illuminating the park lamps and headlamps. When the low beam headlamps are requested, the BCM applies B+ to both low beam headlamp control circuits illuminating the low beam headlamps.

Low Beams - with T4F

The body control module (BCM) monitors three signal circuits from the headlamp switch. When the headlamp switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor to determine if headlamps are required or if daytime running lamps will be activated based on outside lighting conditions. When the headlamp switch is placed in the OFF position, the headlamp switch headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the headlamp switch in the PARK position, the headlamp switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the headlamp switch is placed in the HEADLAMP position, both the headlamp switch park lamps ON signal circuit and the headlamp switch headlamps ON signal circuit are grounded. The BCM responds to the low beam request by applying ground to the low beam relay control circuit which energizes the low beam relay. With the low beam relay energized, the switch contacts close allowing battery voltage to flow through the low beam fuses to the low beam control circuits illuminating the low beam headlamps.

The high beam and flash to pass functions are contained within the turn signal/multifunction switch. The BCM provides the turn signal/multifunction switch with two signal circuits, the high beam signal circuit and the flash to pass signal circuit. When the low beam headlamps are ON and the turn signal/multifunction switch is placed in the high beam position, ground is applied to the BCM through the high beam signal circuit. The BCM responds to the high beam request by applying ground to the high beam relay control circuit which energizes the high beam relay. With the high beam relay energized, the switch contacts close allowing battery voltage to flow through the high beam fuses to the high beam control circuits illuminating the high beam headlamps.

When the turn signal/multifunction switch is momentarily placed in the flash to pass position, ground is applied to the BCM through the flash to pass signal circuit. The BCM responds by applying ground to the high beam relay control circuit which energizes the high beam relay illuminating the high beams for a brief moment or until the flash to pass switch is released.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify the scan tool Headlamps On Switch parameter changes between Active and Inactive while commanding the headlamp ON and OFF with headlamp switch. If the parameter does not change Refer to Headlamp Switch Malfunction below. If the parameter changes
  3. Verify the scan tool Automatic Headlamps Disable Switch parameter changes between Active and Inactive while commanding the automatic lamp control ON and OFF with the turn signal/multifunction switch. If the parameter does not change Refer to Headlamp Switch Malfunction below. If the parameter changes
  4. Verify the scan tool Headlamps Flash Switch parameter changes between Active and Inactive while commanding the flash to pass ON and OFF with the turn signal/multifunction switch. If the parameter does not change Refer to Turn Signal/Multifunction Switch Malfunction below. If the parameter changes
  5. Verify the scan tool High Beam Select Switch parameter changes between Active and Inactive while commanding the high beams ON and OFF with the turn signal/multifunction switch. If the parameter does not change Refer to Turn Signal/Multifunction Switch Malfunction below. If the parameter changes
  6. Verify the left low beam/daytime running lamp turn ON and OFF when commanding the Left Low Beam/Daytime Running Lamp ON and OFF with a scan tool. If the left low beam/daytime running lamp does not turn ON and OFF Refer to Headlamps Malfunction - Low Beam below. If the left low beam/daytime running lamp turns ON and OFF
  7. Verify the right low beam/daytime running lamp turn ON and OFF when commanding the Right Low Beam/Daytime Running Lamp ON and OFF with a scan tool. If the right low beam/daytime running lamp does not turn ON and OFF Refer to Headlamps Malfunction - Low Beam below. If the right low beam/daytime running lamp turns ON and OFF
  8. Verify the high beams turn ON and OFF when commanding the High Beams ON and OFF with a scan tool. If the high beams do not turn ON and OFF Refer to Headlamps Malfunction - High Beam below. If the high beams turn ON and OFF
  9. Verify the high beam indicator on the instrument cluster turns ON and OFF while commanding the All Indicators Test ON and OFF with a scan tool. If the high beam indicator does not turn ON and OFF Refer to High Beam Indicator Malfunction below. If the high beam indicator turns ON and OFF
  10. All OK.

Headlamp Switch Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S30 headlamp switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 6 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Automatic Headlamps Disable Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 5 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the ground circuit terminal 6.
  6. Verify the scan tool Automatic Headlamps Disable Switch parameter is Active. If not Active Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 5 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Verify the scan tool Park Lamps Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 3 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  8. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the ground circuit terminal 6.
  9. Verify the scan tool Park Lamps Switch parameter is Active. If not Active Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 3 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  10. Verify the scan tool Headlamps On Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 4 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  11. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the ground circuit terminal 6.
  12. Verify the scan tool Headlamps On Switch parameter is Active. If not Active Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 4 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  13. Test or replace the S30 headlamp switch.

Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S78 turn signal/multifunction switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 3 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool High Beam Select Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 2 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 2 and the ground circuit terminal 3.
  6. Verify the scan tool High Beam Select Switch parameter is Active. If not Active Ignition OFF, disconnect the X3 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 2 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Verify the scan tool Headlamps Flash Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 4 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  8. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the ground circuit terminal 3.
  9. Verify the scan tool Headlamps Flash Switch parameter is Active. If not Active Ignition OFF, disconnect the X3 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 4 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  10. Test or replace the S78 turn signal/multifunction switch.

Headlamps Malfunction - Low Beam (with T4A)

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E4 headlamp - low beam.
  2. Test for less than 5 ohms between the ground circuit terminal B and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the appropriate Low Beam/Daytime Running Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate E4 headlamp - low beam.

Headlamps Malfunction - Low Beam (with T4F)

  1. Ignition OFF, disconnect the KR49 headlamp low beam relay.
  2. Connect a test lamp between the control circuit terminal 85 and B+, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the Low Beams ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the control circuit terminal and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Ignition OFF, exterior lamps OFF, connect the KR49 headlamp low beam relay.
  5. Disconnect the harness connector at the appropriate E13 headlamp.
  6. Test for less than 5 ohms between the ground circuit terminal G and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  7. Connect a test lamp between the control circuit terminal A and ground, ignition ON.
  8. Verify the test lamp turns ON and OFF when commanding the appropriate Low Beam/Daytime Running Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X1 harness connector at the X50A fuse block - underhood. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the KR49 headlamp low beam relay. If the test lamp is always ON Ignition OFF, disconnect the X1 harness connector at the X50A fuse block - underhood, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the KR49 headlamp low beam relay. If the test lamp turns ON and OFF
  9. Test or replace the appropriate E13 headlamp.

Headlamps Malfunction - High Beam

  1. Ignition OFF, disconnect the X2 harness connector at the X50A fuse block - underhood.
  2. Connect a test lamp between the control circuit terminal 58 and B+, ignition ON.
  3. Verify the test lamp turns ON and OFF when commanding the High Beams ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X5 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X5 harness connector at the K9 body control module. Test for infinite resistance between the control circuit terminal and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If the test lamp turns ON and OFF
  4. Ignition OFF, exterior lamps OFF, connect the X2 harness connector at the X50A fuse block - underhood.
  5. Disconnect the harness connector at the appropriate headlamp - high beam.
  6. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground. E4 high beam headlamp - terminal B (T4A) M28 high beam headlamp solenoid - terminal 1 (T4F) If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  7. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON. E4 high beam headlamp - terminal A (T4A) M28 high beam headlamp solenoid - terminal 2 (T4F)
  8. Verify the test lamp turns ON and OFF when commanding the High Beams ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X1 harness connector at the X50A fuse block - underhood. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the X50A fuse block - underhood. If the test lamp is always ON Ignition OFF, disconnect the X1 harness connector at the X50A fuse block - underhood, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the X50A fuse block - underhood. If the test lamp turns ON and OFF
  9. Test or replace the appropriate headlamp - high beam.

High Beam Indicator Malfunction

  1. Ignition ON.
  2. Verify the high beam indicator turns ON and OFF when commanding the Instrument Cluster All Indicators Test ON and OFF with a scan tool. If the high beam indicator is always OFF or remains ON Replace the P16 instrument cluster. If the high beam indicator turns ON and OFF
  3. Replace the K9 body control module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Headlamp Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Headlamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Headlamp Bulb Replacement (TT4 Low Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT4 High Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Headlamp Ballast Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Turn Signal Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/steering-column-switches/#steering-wheel-and-steering-column)
  6. «Fuse Block Replacement»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  7. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or Instrument Cluster replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
LIN Serial Data - Left Headlamp Leveling ActuatorB3440 03, U1511 00, U1521 00, U1531 00B3440 03, U1511 00, U1521 00, U1531 00B3440 03, U1511 00, U1521 00, U1531 00
LIN Serial Data - Right Headlamp Leveling ActuatorB3435 00, U1512 00, U1522 00, U1532 00B3435 00, U1512 00, U1522 00, U1532 00B3435 00, U1512 00, U1522 00, U1532 00
Headlamp Control Module B+ (F64 UA)11
Headlamp Leveling Actuator - Left B+ (F36 UA)B3435 03B3435 03B3435 00
Headlamp Leveling Actuator - Right B+ (F36 UA)B3440 03B3440 03B3440 00
Suspension Position Sensor 5V Reference - Left FrontB3415 021B3415 01
Suspension Position Sensor 5V Reference - Left RearB3415 021B3415 01
Suspension Position Sensor Signal - Left FrontB3410 06B3410 06B3410 01B3410 08
Suspension Position Sensor Signal - Left RearB3420 06B3420 06B3420 01B3420 08
Suspension Position Sensor Low Reference - Left Front1
Suspension Position Sensor Low Reference - Left Rear1
Headlamp Control Module Ground1
Headlamp Leveling Actuator - Left GroundB3435 03
Headlamp Leveling Actuator - Right GroundB3440 03
1. Headlamp Leveling Malfunction

Each headlamp assembly contains a headlamp leveling actuator that is controlled by the headlamp leveling control module. The front and rear suspension position sensors provide the headlamp leveling control with suspension position information. Each sensor receives a 5 V reference, signal, and low reference circuits from the headlamp leveling control module. The sensors are connected to the control arms of the front and rear suspension. As the vehicle travels, the suspension compresses and rebounds moving the suspension position sensor arms. This causes the signal output of the sensor to change. The headlamp leveling control module compares the information from both suspension position sensors and adjusts the headlamp leveling as needed. The headlamp leveling control module communicates with the left and right headlamp leveling actuators via the LIN serial data circuit.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Engine RUNNING.
  2. Verify the scan tool Front Leveling Position Sensor Voltage parameter is between 0.5 and 4.9 V. If the parameter is not between 0.5 and 4.9 V Refer to Headlamp Leveling Sensor Malfunction below. If the parameter is between 0.5 and 4.9 V
  3. Verify the scan tool Rear Leveling Position Sensor Voltage parameter is between 0.5 and 4.9 V. If the parameter is not between 0.5 and 4.9 V Refer to Headlamp Leveling Sensor Malfunction below. If the parameter is between 0.5 and 4.9 V
  4. Verify the left and right headlamps operate to the UP and DOWN positions when commanding the DHL Motor Control UP and DOWN with a scan tool. If the left and right headlamps do not operate UP and DOWN Refer to Headlamp Leveling Actuator Malfunction below. If the left and right headlamps operate UP and DOWN
  5. All OK.

Headlamp Leveling Actuator Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E13 headlamp assembly.
  2. Test for less than 5 ohms between the ground circuit terminals listed below and ground. Terminal G Terminal H Terminal J If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Ignition ON.
  4. Verify a test lamp illuminates between the B+ circuit terminal B and ground. If the test lamp does not illuminate Ignition OFF, disconnect the X1 harness connector at the X50A fuse block - underhood. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the X50A fuse block - underhood. If the test lamp illuminates
  5. Test or replace the K26 headlamp control module.
  6. Ignition ON.
  7. Verify the appropriate headlamp operates to the UP and DOWN positions when commanding the DHL Motor Control UP and DOWN with a scan tool. If the appropriate headlamp does not operate UP and DOWN, test or replace the appropriate headlamp assembly.

Headlamp Leveling Sensor Malfunction

  1. Ignition OFF, disconnect the harness connector at the appropriate B152L suspension position sensor, ignition ON.
  2. Verify a test lamp illuminates between the low reference circuit terminal 1 and B+. If the test lamp does not illuminate Ignition OFF, disconnect the X1 harness connector at the K26 headlamp control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K26 headlamp control module. If the test lamp illuminates
  3. Ignition ON.
  4. Test for 4.8-5.2 V between the 5 V reference circuit terminal 3 and ground. If less than 4.8 V Ignition OFF, disconnect the X1 harness connector at the K26 headlamp control module. Test for infinite resistance between the 5 V reference circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the 5 V reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K26 headlamp control module. If greater than 5.2 V Ignition OFF, disconnect the X1 harness connector at the K26 headlamp control module, ignition ON. Test for less than 1 V between the 5 V reference circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K26 headlamp control module. If between 4.8-5.2 V
  5. Verify the appropriate scan tool Leveling Position Sensor parameter is less than 1 V. If 1 V or greater Ignition OFF, disconnect the X1 harness connector at the K26 headlamp control module, ignition ON. Test for less than 1 V between the signal circuit terminal 2 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K26 headlamp control module. If less than 1 V
  6. Install a 3 A fused jumper wire between the 5-volt reference circuit terminal 3 and the signal circuit terminal 2 engine RUNNING.
  7. Verify the appropriate scan tool Leveling Position Sensor parameter is greater than 4.8 V. If less than 4.8 V Ignition OFF, disconnect the X1 harness connector at the K26 headlamp control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K26 headlamp control module. If 4.8 V or greater
  8. Test or replace the appropriate B152L suspension position sensor.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Headlamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for headlamp control module replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Accent Lamp Control - Terminal 7 X6B2652 0211
Accent Lamp - Driver Door Ground1
Accent Lamp - Driver Door Handle Ground1
Accent Lamp - Passenger Door Ground1
Accent Lamp - Passenger Door Handle Ground1
Accent Lamp - Left Instrument Panel Ground1
Accent Lamp - Lower Instrument Panel Ground1
Accent Lamp - Right Instrument Panel Ground1
Accent Lamp - Right Rear Door Ground1
Accent Lamp - Right Rear Door Handle Ground1
Accent Lamp - Left Rear Door Ground1
Accent Lamp - Left Rear Door Handle Ground1
Accent Lamp - Center Console Armrest Left Ground1
Accent Lamp - Center Console Armrest Right Ground1
Accent Lamp - Center Console Cupholder Left Ground1
Accent Lamp - Center Console Cupholder Right Ground1
1. Interior Accent Lighting Malfunction

The instrument panel dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The instrument panel dimmer switch provides a voltage signal to the body control module (BCM) that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The BCM provides a low reference signal and B+ to the instrument panel dimmer switch. When the instrument panel dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies a pulse width modulated (PWM) voltage through the LED dimming control circuits illuminating the interior backlighting to the requested level of brightness.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the appropriate E1 accent lamp. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the appropriate ground circuit terminal and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Connect a test lamp between the appropriate control circuit terminal and ground.
  4. Verify the test lamp turns ON and OFF while turning the headlamp switch ON and OFF. If the test lamp is always OFF Ignition OFF, disconnect the X6 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X6 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate E1 accent lamp

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Front Floor Console Cup Holder Illumination Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Front Floor Console Armrest Compartment Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Front Side Door Inside Handle Illumination Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Rear Side Door Inside Handle Illumination Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Instrument Panel Dimmer Switch B+B1405 03, B1529 03, B257B 03B257B 03
Instrument Panel Dimmer Switch SignalB257B 03B257B 03B257B 07
LED Backlight Dimming Control Terminal 8 X2B2610 02B2610 042
LED Backlight Dimming Control Terminal 9 X7B2610 02B2610 042
Object Detection Switch Indicator LED Backlight Dimming Control Terminal 5 X1B2625 0222
Dome/Reading Lamps - Front Ground2
Dome/Reading Lamps - 2nd Row Ground2
Garage Door Opener Ground2
Headlamp Switch Ground1
Head - Up Display Switch Ground2
Ignition Mode Switch Ground2
Multifunction Switch 1 - Instrument Panel Ground2
Multifunction Switch 2 - Instrument Panel Ground2
Outside Rearview Mirror Switch Ground2
Park Brake Control Switch Ground2
Sunroof Switch Ground2
Sunroof Sunshade Switch Ground2
Steering Wheel Controls Switch - Left Ground2
Steering Wheel Controls Switch - Right Ground2
Window Switch - Passenger Ground2
1. Dimmer Switch Malfunction 2. Interior Backlighting Malfunction

The instrument panel dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The instrument panel dimmer switch provides a voltage signal to the body control module (BCM) that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The BCM provides a low reference signal and a B+ circuit to the instrument panel dimmer switch. When the instrument panel dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies a pulse width modulated (PWM) voltage through the LED dimming 1 and dimming 2 control circuits illuminating the interior backlighting to the requested level of brightness.

Schematic Reference

  1. «Interior Lights Dimming Schematics»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-wiring-schematic-diagrams)
  2. «Object Detection Schematics»(/buick/lacrosse/ii-2009-2013/remont/collisionavoidance/#object-detection-system-park-assist-system)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify the scan tool LED Backlight Dimming Command parameter changes between a high percentage to a low percentage while operating the dimmer switch from high to low. If the parameter does not change Refer to Dimmer Switch Malfunction below. If the parameter changes
  3. Verify all backlighting components turn ON and OFF while commanding the LED Backlight Dimming ON and OFF with a scan tool. If all backlighting components do not turn ON and OFF Refer to Interior Backlighting Malfunction below. If all backlighting components turn ON and OFF
  4. All OK.

Dimmer Switch Malfunction

  1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the S30 headlamp switch, ignition ON.
  2. Test for B+ between the B+ circuit terminal 1 and ground. If less than B+ Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If B+
  3. Verify the scan tool LED Backlight Dimming Command parameter is greater than 40%. If 40% or less Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 12 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If greater than 40%
  4. Install a 3 A fused jumper wire between the signal circuit terminal 12 and the B+ circuit terminal 1.
  5. Verify the scan tool LED Backlight Dimming Command parameter is less than 30%. If 30% or greater Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If less than 30%
  6. Test or replace the S30 headlamp switch.

Interior Backlighting Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the component with inoperative backlighting. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the appropriate ground circuit terminal and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Connect a test lamp between the appropriate control circuit terminal and ground.
  4. Verify the test lamp turns ON and OFF when commanding the LED Backlight Dimming ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the appropriate harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the appropriate harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the component with inoperative backlighting.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Dome and Reading Lamp Replacement - Front»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Dome and Reading Lamp Replacement - Rear»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Sunroof Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/sun-rooft-topconvertible-top/#sunroof-system)
  4. «Outside Remote Control Rearview Mirror Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/mirrors/#mirror-system)
  5. «Front Side Door Window and Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/heated-glassdefoggers/#fixed-and-moveable-windows)
  6. «Rear Side Door Window Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/heated-glassdefoggers/#fixed-and-moveable-windows)
  7. «Headlamp Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  8. «Parking Brake Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/parking-brake-system/#parking-brake-system)
  9. «Instrument Panel Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
  10. «Accessory Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/gauges-instrument-panels/#instrument-panel-system-displays-and-gauges)
  11. «Radio and Telephone Control Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/entertainment-systems/#cellular-system-entertainment-system-and-navigation-system)
  12. «Cruise Control Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/cruise-control-systems/#cruise-control-system)
  13. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, HVAC, instrument cluster, or radio replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F3DA (BCM 5) Fuse B+B2585 01, B2585 04B2585 01, B2585 04
F24DA (BCM 2) Fuse B+B3867 01, B3867 04B3867 01, B3867 04
Headlamp Switch Park Lamps ON Signal2B257A 002
Park Lamps Control - LeftB2585 02B2585 01, B2585 04B2585 01, B2585 04
Park Lamps Control - RightB3867 02B3867 01, B3867 04B3867 01, B3867 04
Headlamp Switch Ground2
Park/Turn Signal Lamp Ground - Left Front1
Park/Turn Signal Lamp Ground - Right Front1
Side Marker Lamp Ground - Left Front1
Side Marker Lamp Ground - Left Rear1
Side Marker Lamp Ground - Right Front1
Side Marker Lamp Ground - Right Rear1
Tail Lamp Ground - Left1
Tail Lamp Ground - Right1
1. Park, License, and/or Tail Lamps Malfunction 2. Park Lamp Switch Malfunction

When the headlamp switch is placed in the HEAD or PARK position, ground is applied to the park lamp switch ON signal circuit to the body control module (BCM). The BCM responds by applying voltage to the park lamps, tail lamps, and license lamps control circuits illuminating the park, tail, and license lamps.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify the scan tool Park Lamp Switch parameter changes between Active and Inactive while commanding the park lamps ON and OFF with the turn signal/multifunction switch. If the parameter does not change Refer to Headlamp Switch Malfunction below. If the parameter changes
  3. Verify the left park lamps turn ON and OFF when commanding the Left Park Lamps ON and OFF with a scan tool. If the left park lamps do not turn ON and OFF Refer to Park Lamps Malfunction below. If the left park lamps turn ON and OFF
  4. Verify the right park lamps turn ON and OFF when commanding the Right Park Lamps ON and OFF with a scan tool. If the right park lamps do not turn ON and OFF Refer to Park Lamps Malfunction below. If the right park lamps turn ON and OFF
  5. Verify the license plate lamps turn ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool. If the license plate lamps do not turn ON and OFF Refer to License Plate Lamps Malfunction below. If the license plate lamps turn ON and OFF
  6. All OK.

Headlamp Switch Malfunction

  1. Ignition OFF, all doors closed, all accessories OFF, disconnect the harness connector at the S30 headlamp switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 6 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Park Lamps Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X1 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 3 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the ground circuit terminal 6.
  6. Verify the scan tool Park Lamps Switch parameter is Active. If not Active Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 3 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Test or replace the S30 headlamp switch.

Park Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, trunk latch latched, disconnect the harness connector at the inoperative park/marker/tail lamp.
  2. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground. E4N park/turn signal lamp - left terminal G E2LF side marker lamp - left front terminal 2 E2LR side marker lamp - left rear terminal B E5AA tail/stop lamp - left terminal 1 E4P park/turn signal lamp - right terminal G E2RF side marker lamp - right front terminal 2 E2RR side marker lamp - right rear terminal B E5AB tail/stop lamp - right terminal 1 If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground, ignition ON. E4N park/turn signal lamp - left terminal B E2LF side marker lamp - left front terminal 1 E2LR side marker lamp - left rear terminal A E5AA tail/stop lamp - left terminal 3 E4P park/turn signal lamp - right terminal B E2RF side marker lamp - right front terminal 1 E2RR side marker lamp - right rear terminal A E5AB tail/stop lamp - right terminal 3
  4. Verify the test lamp turns ON and OFF when commanding the appropriate Park Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate park/marker/tail lamp.

License Plate Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, remove both E7 license plate lamp bulbs.
  2. Test for less than 5 ohms between the ground circuit terminal 2 and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Connect a test lamp between the license plate lamp - left control circuit terminal 1 and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Connect a test lamp between the license plate lamp - right control circuit terminal 1 and ground, ignition ON.
  6. Verify the test lamp turns ON and OFF when commanding the License Plate Lamps ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp turns ON and OFF
  7. Test or replace the appropriate E7 license plate lamp bulb.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Rear License Plate Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Headlamp Bulb Replacement (TT4 Low Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT2)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions) , «Headlamp Bulb Replacement (TT4 High Beam)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Tail Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  4. «Front Turn Signal Lamp Bulb Replacement (TT4)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
F8DA (BCM 1) Fuse B+C0890 03, U0121 00C0890 03, U0121 00
Brake Pedal Position Sensor 5 V ReferenceC0277 06, C0890 03, C0161 71C0277 06, C0161 71, C0161 5AC0277 07, C0890 07, C0161 71
Brake Pedal Position Sensor SignalC0277 06, U0140 71C0277 06, C0161 71, C0161 5AC0277 07, C0890 07, C0161 71C0277 09
Center High Mounted Stop Lamp Control222
Stop Lamp Control - Left111
Stop Lamp Control - Right111
Brake Pedal Position Sensor Low ReferenceC0277 07, C0161 71U0151 00, U0184 00
Center High Mounted Stop Lamp Ground2
Tail/Stop Lamp Ground - Left1
Tail/Stop Lamp Ground - Right1
1. Stop Lamps Malfunction 2. Center High Mounted Stop Lamp Malfunction

The brake pedal position (BPP) sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module provides a low reference signal and a 5 V reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the left and right stop lamp control circuits as well as the center high mounted stop lamp (CHMSL) control circuit illuminating the left and right stop lamps and the CHMSL.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify the scan tool Brake Pedal Applied parameter changes between Active and Inactive while pressing and releasing the brake pedal. If the parameter does not change Refer to Brake Pedal Position Sensor Malfunction below. If the parameter changes
  3. Verify the left brake lamp turns ON and OFF when commanding the Left Brake Lamp ON and OFF with a scan tool. If the left brake lamp does not turn ON and OFF Refer to Stop Lamps Malfunction below. If the left brake lamp turns ON and OFF
  4. Verify the right brake lamp turns ON and OFF when commanding the Right Brake Lamp ON and OFF with a scan tool. If the right brake lamp does not turn ON and OFF Refer to Stop Lamps Malfunction below. If the right brake lamp turns ON and OFF
  5. Verify the center high mounted stop lamp turns ON and OFF when commanding the Center Brake Lamp ON and OFF with a scan tool. If the center high mounted stop does not turn ON and OFF Refer to Center High Mount Stop Lamp Malfunction below. If the center high mounted stop turns ON and OFF
  6. All OK.

Brake Pedal Position Sensor Malfunction

  1. Ignition OFF, disconnect the harness connector at the B22 brake pedal position sensor, ignition ON.
  2. Test for less than 1 V between the low reference circuit terminal 1 and ground. If 1 V or greater Ignition OFF, disconnect the X1 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the low reference circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If less than 1 V
  3. Test or replace the B22 brake pedal position sensor.

Stop Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E5 tail/stop lamp.
  2. Test for less than 10 ohms between the ground circuit terminal 1 and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Connect a test lamp between the control circuit terminal 2 and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the appropriate Brake Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the appropriate harness connector listed below at the K9 body control module. X4 left stop lamp X5 right stop lamp Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the appropriate harness connector listed below at the K9 body control module, ignition ON. X4 left stop lamp X5 right stop lamp Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate E5 tail/stop lamp.

Center High Mount Stop Lamp Malfunction

  1. Ignition OFF, exterior lamps OFF, trunk latch latched, disconnect the harness connector at the E6 center high mounted stop lamp.
  2. Test for less than 10 ohms between the ground circuit terminal A and ground. If 10 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
  3. Connect a test lamp between the control circuit terminal B and ground, ignition ON.
  4. Verify the test lamp turns ON and OFF when commanding the Center Brake Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X4 harness connector at the K9 body control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the X4 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the E6 center high mounted stop lamp.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «High Mount Stop Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  2. «Tail Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Brake Pedal Position Sensor Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions__brake-pedal-position-sensor-replacement)
  4. «Brake Pedal Position Sensor Calibration»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions__brake-pedal-position-sensor-calibration)
  5. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/buick/lacrosse/ii-2009-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Turn Signal Switch Signal - Left111
Turn Signal Switch Signal - Right111
Turn Signal Control - Left FrontB3948 02B3948 04B3948 01, B3948 04
Turn Signal Control - Left RearB3950 02B3950 04B3950 01, B3950 04
Turn Signal Control - Right FrontB3949 02B3949 04B3949 01, B3949 04
Turn Signal Control - Right RearB3951 02B3951 04B3951 01, B3951 04
Turn Signal Lamp Ground - Left FrontB3948 01, B3948 04
Turn Signal Lamp Ground - Right FrontB3949 01, B3949 04
Turn Signal Lamp Ground - Left RearB3950 01, B3950 04
Turn Signal Lamp Ground - Right RearB3951 01, B3951 04
Turn Signal Repeater Lamp - Left GroundB3948 01, B3948 04
Turn Signal Repeater Lamp - Right GroundB3949 01, B3949 04
Turn Signal/Multifunction Switch Ground1
1. Turn Signal Lamps and/or Indicators Malfunction

Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START positions. When the turn signal/multifunction switch is placed in either the turn right or turn left position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM responds to the turn signal switch input by applying a pulsating voltage to the front and rear turn signal lamps through there respective control circuits. When a turn signal request is received by the BCM, a serial data message is sent to the instrument cluster requesting the respective turn signal indicator be pulsed ON and OFF.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/buick/lacrosse/ii-2009-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify the scan tool Right Turn Signal Switch and Left Turn Signal Switch parameters change between Active and Inactive while cycling the turn signal switch between the right and left positions. If the parameters do not change Refer to Turn Signal/Multifunction Switch Malfunction below. If the parameters change
  3. Verify the left front turn signal lamps turn ON and OFF while commanding the Left Front Turn Signal Lamp ON and OFF with a scan tool. If the left front turn signal lamps do not turn ON and OFF Refer to Turn Signal Lamps Malfunction below. If the left front turn signal lamps turn ON and OFF
  4. Verify the right front turn signal lamps turn ON and OFF while commanding the Right Front Turn Signal Lamp ON and OFF with a scan tool. If the right front turn signal lamps do not turn ON and OFF Refer to Turn Signal Lamps Malfunction below. If the right front turn signal lamps turn ON and OFF
  5. Verify the left rear turn signal lamp turns ON and OFF while commanding the Left Rear Turn Signal Lamp ON and OFF with a scan tool. If the left rear turn signal lamp does not turn ON and OFF Refer to Turn Signal Lamps Malfunction below. If the left rear turn signal lamp turns ON and OFF
  6. Verify the right rear turn signal lamp turns ON and OFF while commanding the Right Rear Turn Signal Lamp ON and OFF with a scan tool. If the right rear turn signal lamp does not turn ON and OFF Refer to Turn Signal Lamps Malfunction below. If the right rear turn signal lamp turns ON and OFF
  7. Verify the left and right turn signal indicators turn ON and OFF while commanding the All Indicators Test ON and OFF with a scan tool. If the left or right turn signal indictors do not turn ON and OFF Refer to Turn Signal Indicators Malfunction below. If the left and right turn signal indictors turn ON and OFF
  8. All OK.

Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, scan tool disconnected, all doors closed, all accessories OFF, disconnect the harness connector at the S78 turn signal/multifunction switch. It may take up to 2 minutes for all vehicle systems to power down.
  2. Test for less than 15 ohms between the ground circuit terminal 3 and ground. If 15 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 15 ohms
  3. Ignition ON.
  4. Verify the scan tool Left Turn Signal Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 1 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  5. Install a 3 A fused jumper wire between the signal circuit terminal 1 and the ground circuit terminal 3.
  6. Verify the scan tool Left Turn Signal Switch parameter is Active. If not Active Ignition OFF, disconnect the X3 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 1 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  7. Verify the scan tool Right Turn Signal Switch parameter is Inactive. If not Inactive Ignition OFF, disconnect the X3 harness connector at the K9 body control module. Test for infinite resistance between the signal circuit terminal 7 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the K9 body control module. If Inactive
  8. Install a 3 A fused jumper wire between the signal circuit terminal 7 and the ground circuit terminal 3.
  9. Verify the scan tool Right Turn Signal Switch parameter is Active. If not Active Ignition OFF, disconnect the X3 harness connector at the K9 body control module, ignition ON. Test for less than 1 V between the signal circuit terminal 7 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If Active
  10. Test or replace the S78 turn signal/multifunction switch.

Turn Signal Lamps Malfunction

  1. Ignition OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E4 turn signal lamp.
  2. Test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground. A9A outside rearview mirror - driver terminal 4 E4N park/turn signal lamp - left front terminal G E4LR turn signal lamp - left rear terminal G A9B outside rearview mirror - passenger terminal 4 E4P turn signal lamp - right front terminal G E4RR turn signal lamp - right rear terminal G If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
  3. Connect a test lamp between the appropriate control circuit terminal listed below and ground. A9A outside rearview mirror - driver terminal 16 E4N turn signal lamp - left front terminal A E4LR turn signal lamp - left rear terminal A A9B outside rearview mirror - passenger terminal 16 E4P turn signal lamp - right front terminal A E4RR turn signal lamp - right rear terminal A
  4. Verify the test lamp turns ON and OFF when commanding the appropriate Turn Signal Lamp ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the appropriate harness connector listed below at the K9 body control module. X4 right turn signals X5 left turn signals Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the K9 body control module. If the test lamp is always ON Ignition OFF, disconnect the appropriate harness connector listed below at the K9 body control module, ignition ON. X4 right turn signals X5 left turn signals Test for less than 1 V between the control circuit terminal and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K9 body control module. If the test lamp turns ON and OFF
  5. Test or replace the appropriate turn signal lamp.

Turn Signal Indicators Malfunction

  1. Ignition ON.
  2. Verify the left and right turn signal indicators turn ON and OFF while commanding the All Indicators Test ON and OFF with a scan tool. If the left or right turn signal indictors are always OFF or remain ON Replace the P16 instrument cluster. If the left and right turn signal indictors turn ON and OFF
  3. Replace the K9 body control module.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «Turn Signal Multifunction Switch Replacement»(/buick/lacrosse/ii-2009-2013/remont/steering-column-switches/#steering-wheel-and-steering-column)
  2. «Tail Lamp Replacement»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  3. «Outside Rearview Mirror Replacement»(/buick/lacrosse/ii-2009-2013/remont/mirrors/#mirror-system)
  4. «Front Turn Signal Lamp Bulb Replacement (TT4)»(/buick/lacrosse/ii-2009-2013/remont/exterior-lights/#lighting-system-repair-instructions)
  5. «Control Module References»(/buick/lacrosse/ii-2009-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or instrument cluster replacement, programming, and setup

See also:
• Diagnostic System Check - Vehicle
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
• Exterior Lights Schematics
• COMPONENT CONNECTOR END VIEWS - INDEX
• Interior Lighting Systems Description and Operation
• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs
• Control Module References
• Diagnostic Repair Verification
• Instrument Panel Multifunction Switch Replacement
• Power Mode Description and Operation
• Sunshade Replacement
• Instrument Panel Compartment Lamp Replacement
• Fuse Block Replacement
• Body Control System Schematics
• Relay Replacement (Within an Electrical Center)
• Sunroof Switch Replacement
• Outside Remote Control Rearview Mirror Switch Replacement
• Front Side Door Window and Multifunction Switch Replacement
• Parking Brake Switch Replacement
• Radio and Telephone Control Switch Replacement
• Cruise Control Switch Replacement
• Object Detection Schematics
• Sun Load Temperature and Headlamp Automatic Control Ambient Light Sensor Replacement
• Turn Signal Multifunction Switch Replacement
• Brake Pedal Position Sensor Calibration
• Brake Pedal Position Sensor Replacement
• Cruise Control Description and Operation
• Checking Aftermarket Accessories
• Cigar Lighter/Power Outlet Schematics
• Adaptive Forward Lighting Malfunction

More articles — Lighting