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Contents Section: Exterior Lights All sections

Lighting System GMC Sierra 2500

Exterior Lights 54 illustrations ~29140 words

Fastener Tightening Specifications

ApplicationSpecification
MetricEnglish
Center High-Mounted Stop Cargo Lamp Mounting Screws2.5 N.m22 lb in
Headlamp Ballast Screws2 N.m18 lb in
Headlamp Mounting Screws6 N.m53 lb in
License Plate Lamp Screws2 N.m18 lb in
Power Vacuum Brake Booster Pushrod Retaining Bolt10 N.m89 lb in
Rear Tail/Turn Signal Lamp Assembly Screws2 N.m18 lb in
Rear Side Marker Lamp Screws2.5 N.m22 lb in
Roof Marker Lamp Screws- Center2 N.m18 lb in
Roof Marker Lamp Screws- Outer2 N.m18 lb in
Tail Lamp Screws2 N.m18 lb in

Fastener Tightening Specifications

Scheme 1

Scheme 1: Headlight And Daytime Running Light Control
Scheme 1: Headlight And Daytime Running Light Control

Scheme 2

Scheme 2: Low Beam And Daytime Running Lights
Scheme 2: Low Beam And Daytime Running Lights

Scheme 3

Scheme 3: High Beams
Scheme 3: High Beams

Scheme 4

Scheme 4: Fog Lights
Scheme 4: Fog Lights

Scheme 5

Scheme 5: Park Lamp Controls And Front Park Lamps
Scheme 5: Park Lamp Controls And Front Park Lamps

Scheme 6

Scheme 6: Left Rear Park Lamps
Scheme 6: Left Rear Park Lamps

Scheme 7

Scheme 7: Right Rear Park Lamps
Scheme 7: Right Rear Park Lamps

Scheme 8

Scheme 8: Exterior Illumination Lamps (DL3 Or DR4)
Scheme 8: Exterior Illumination Lamps (DL3 Or DR4)

Scheme 9

Scheme 9: Turn Signal Controls And Front Turn Signal Lamps
Scheme 9: Turn Signal Controls And Front Turn Signal Lamps

Scheme 10

Scheme 10: Rear Stop/Turn Signal Lamps
Scheme 10: Rear Stop/Turn Signal Lamps

Scheme 11

Scheme 11: Stop Lamp Controls
Scheme 11: Stop Lamp Controls

Scheme 12

Scheme 12: Backup Lamps And Backup Alarm
Scheme 12: Backup Lamps And Backup Alarm

Scheme 13

Scheme 13: Inadvertent Lamp Control
Scheme 13: Inadvertent Lamp Control

Scheme 14

Scheme 14: Courtesy Lamp Control
Scheme 14: Courtesy Lamp Control

Scheme 15

Scheme 15: Door Jamb Switches (AN3 Or DL3)
Scheme 15: Door Jamb Switches (AN3 Or DL3)

Scheme 16

Scheme 16: Door Jamb Switches (except AN3 Or DL3)
Scheme 16: Door Jamb Switches (except AN3 Or DL3)

Scheme 17

Scheme 17: Dimming Control And LED Dimming (1 Of 3)
Scheme 17: Dimming Control And LED Dimming (1 Of 3)

Scheme 18

Scheme 18: LED Dimming (2 Of 3)
Scheme 18: LED Dimming (2 Of 3)

Scheme 19

Scheme 19: LED Dimming (3 Of 3)
Scheme 19: LED Dimming (3 Of 3)

Scheme 20

Scheme 20: I/P Bulb Dimming (2 Of 2)
Scheme 20: I/P Bulb Dimming (2 Of 2)

Scheme 21

Scheme 21: I/P Bulb Dimming (2 Of 2)
Scheme 21: I/P Bulb Dimming (2 Of 2)

Diagnostic Code Index

DTCDescription
DTC B1395DTC B1395 03 Device Voltage Reference Output 1 Circuit Voltage Below Threshold DTC B1395 07 Device Voltage Reference Output 1 Circuit Voltage Above Threshold
DTC B2530DTC B2530 00 Front Fog Lamp Control Circuit
DTC B2545DTC B2545 00 Backup Lamps Circuit
DTC B2555DTC B2555 01 Passenger Compartment Lamp Control Circuit Short to Battery DTC B2555 02 Passenger Compartment Lamp Control Circuit Short to Ground
DTC B2575DTC 2575 00 Headlamp Low Beam Control Circuit
DTC B257ADTC B257A 00 Headlamp Switch Input Signal Mismatch
DTC B2580DTC B2580 00 Headlamp High Beam Control Circuit
DTC B2585DTC B2585 00 Park Lamp Control Circuit
DTC B2600DTC B2600 00 Daytime Running Lamp Control Circuit
DTC B2610DTC B2610 00 Passenger Compartment Dimming 1 Circuit
DTC B2615DTC B2615 00 Passenger Compartment Dimming 2 Circuit
DTC B2625DTC B2625 00 Display Dimming Pulse Width Modulation (PWM) Output Circuit
DTC B2635DTC B2635 00 Passenger Compartment Dimming 2 Circuit
DTC B2645DTC B2645 03 Ambient Light Sensor Circuit Voltage Below Threshold DTC B2645 07 Ambient Light Sensor Circuit Voltage Above Threshold
DTC B2652DTC B2652 00 Passenger Compartment Dimming 3
DTC B3445DTC B3445 00 Stop Lamp Circuit
DTC B3600DTC B3600 03 Passenger Compartment Dimming Request Signal Voltage Below Threshold DTC B3600 07 Passenger Compartment Dimming Request Signal Voltage Above Threshold
DTC B3884DTC B3884 00 Center High Mounted Stop Lamp (CHMSL) Circuit
DTC C0277 or C0890DTC C0277 06 Brake Pedal Position Sensor Circuit Short to Ground or Open DTC C0277 07 Brake Pedal Position Sensor Circuit Voltage Above Threshold DTC C0277 09 Brake Pedal Position Sensor Circuit Rate of Change Above Threshold DTC C0277 4B Brake Pedal Position Sensor Calibration Not Learned DTC C0890 03 Device Voltage Reference Output 3 Circuit Voltage Below Threshold DTC C0890 07 Device Voltage Reference Output 3 Circuit Voltage Above Threshold
DTC C0297DTC C0297 00 Brake Applied Output Circuit

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
I/P Dimming Voltage ReferenceB1395 03, B3600 03B1395 03, B2652 00, B3600 03B1395 07B1395 03, B1395 07
Stop Lamp SignalB1395 03, B3600 03

Circuit/System Description

Voltage for the interior backlighting components and stop lamp switch activation signal is supplied from the body control module (BCM). The BCM applies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp dimming switch, which is part of the headlamp switch. When the dimming switch is placed in the desired position, the dimmed voltage setting is applied from the interior lamp dimming switch through the I/P dimming control circuit to the BCM. The BCM then applies the dimmed voltage to the I/P lamps supply voltage circuit and they dim to the correct level.

The stop lamp switch is also supplied voltage on the same circuit for a stop lamp OFF signal to the BCM. When the stop lamp switch is activated the voltage signal circuit to the BCM is opened prompting the BCM to illuminate the stop lamps.

Conditions for Running the DTC

Battery Voltage must be between 9-16 V.

Conditions for Setting the DTC

B1395 03

The BCM detects a voltage that is lower than 0.33 V on the I/P dimming voltage reference circuit.

B1395 07

The BCM detects a voltage that is greater than 4.97 V on I/P dimming voltage reference circuit.

Action Taken When the DTC Sets

  1. The I/P dimmer switch will not operate.
  2. The I/P dimming lamps will not illuminate.

Conditions for Clearing the DTC

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

Reference Information

Schematic Reference

  1. «Interior Lights Dimming Schematics»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Exterior Lights Schematics»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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, cover the ambient light sensor. Vary the interior lamp dimming switch from dim to full bright. The I/P lamps should dim and then become full bright.

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Verify that a test lamp illuminates between B+ and the ground circuit terminal 8. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.1 V. If greater than the specified range, test the signal circuit terminal 13 for a short to voltage. If the circuit tests normal, replace the BCM.
  4. Ignition ON, test for B+ between the I/P dimming voltage reference circuit terminal 15 and ground. If less than the specified value, test the voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal 13 and the voltage reference circuit terminal 15. Verify the scan tool Dimming Control Signal parameter is greater than 2.6 V. If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
Fog Lamp Relay B+11
Fog Lamp Switch Signal222
Fog Lamp Relay Control11B2530 00
Fog Lamp Control111
Fog Lamp - LF Ground1
Fog Lamp - RF Ground1
Fog Lamp Switch Ground2
1. Fog Lamps Malfunction 2. Fog Lamp Switch Malfunction

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

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

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

Actions Taken When the DTC Sets

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

  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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 fog lamp 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 85 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. 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 an open/high resistance.
  5. Disconnect the harness connector at the appropriate fog lamp - front.
  6. Test for less than 5 ohms between the fog lamp - front ground circuit terminal B and ground If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the fog lamp - front.
  8. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the fog lamp - front is activated. If the fog lamp - front does not activate and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the fog lamp - front. If the fog lamp - front does not activate and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the fog lamp - front.
  9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  10. Command the Fog 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 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 BCM.
  11. If all circuits test normal, test or replace the fog lamp relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Front Fog Lamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Front Fog Lamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
Backup Lamp Relay B+11
Backup Lamp Switch Signal111
Backup Lamp Relay ControlB2545 0011
Backup Lamps Control111
Backup Lamp - Left Ground1
Backup Lamp - Right Ground1
Backup Lamp Switch Ground1
1. Backup Lamps Malfunction

Automatic Transmission

When the transmission is placed 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 voltage to the backup lamp relay control circuit energizing the backup lamp relay coil. With the relay coil energized, the switch contacts close allowing battery voltage to flow through the VEH BCK/UP fuse to the left and right backup lamps. The BCM also supplies voltage the to inside rearview mirror via the backup lamp relay control circuit for automatic day/night operation. Once the driver moves the gear selector out of the REVERSE position, a serial data message is sent by the TCM requesting the BCM to remove voltage from the backup lamp control circuit. The engine may need to be running for the backup lamps to function.

Manual Transmission

When the transmission is placed in the REVERSE position, the backup lamp switch contacts close supplying ground to the engine control module (ECM) via the backup lamp switch signal circuit. The ECM responds by sending a serial data message to the body control module (BCM) indicating the gear selector is in the REVERSE position. The BCM applies voltage to the backup lamp relay control circuit energizing the backup lamp relay coil. With the relay coil energized, the switch contacts close allowing battery voltage to flow through the VEH BCK/UP fuse to the left and right backup lamps. The BCM also supplies voltage the to inside rearview mirror via the backup lamp relay control circuit for automatic day/night operation. Once the driver moves the gear selector out of the REVERSE position, the backup lamp switch contacts open and a serial data message is sent by the ECM requesting the BCM to remove voltage from the backup lamp relay control circuit.

Battery voltage must be between 9-16 V.

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

The backup lamps 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 inside rearview mirror.
  2. Connect a test lamp between the control circuit terminal 9 and ground.
  3. Command the Backup 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 voltage. If the circuit tests normal, replace the 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 BCM.
  4. Ignition OFF, connect the harness connector at the inside rearview mirror. Disconnect the X5 harness connector at the underhood fuse block.
  5. Connect a test lamp between the control circuit terminal H8 and ground.
  6. Command the Backup 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 voltage. If the circuit tests normal, replace the 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 BCM.
  7. If all circuits test normal, replace the underhood fuse block.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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 Courtesy Lamp Control CircuitB2555 021B2555 01
Right Courtesy Lamp Control CircuitB2555 021B2555 01
Courtesy Lamp Ground1
1. Courtesy Lamps Inoperative

When the body control module (BCM) signals for courtesy lamp operation, a message is sent over the serial data circuit to the driver door and passenger door switches. The driver door switch and passenger door switch the applies battery voltage to the left and right courtesy lamp control circuits illuminating the door courtesy lamps. The driver door and passenger door switches also provide ground to the lamps.

  1. Battery voltage must be between 9-16 V.
  2. A message is sent from the BCM over the serial data circuit to the driver door and passenger door switches to active the door courtesy lamps.

B2555 01

The driver or passenger door switch detects a short to voltage in the courtesy lamp control circuit.

B2555 02

The driver or passenger door switch detects a short to ground in the courtesy lamp control circuit.

  1. The condition responsible for setting the DTC no longer exists.
  2. A scan tool CLEAR DTCs command is issued for that switch module.
  3. 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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

Note. Each courtesy lighting component may need to be disconnected to isolate a short to voltage or short to ground. Use the schematic to identify the following: Courtesy lighting components the vehicle is equipped with. Component locations on the courtesy lighting control circuit Each component's control and ground circuit terminals

  1. Ignition OFF, disconnect the harness connector at any component with inoperative courtesy lighting.
  2. Ignition OFF, scan tool disconnected, interior lamps OFF, doors CLOSED, test for less than 5 ohms between the ground circuit 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 and ground.
  4. Command the Courtesy Lamp control 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, replace the component with the inoperative backlighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Dome Lamp Replacement»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for driver or passenger door switch replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
HDLP LO/HID Relay B+111
HI Beam Relay B+111
Flash to Pass Switch Signal111
Headlamp Switch Headlamps ON SignalB257A 0011
Headlamp Switch Headlamps OFF SignalB257A 0011
Headlamp Switch High Beam Signal111
Headlamp High Beam Relay Control11B2580 00
Headlamp Low Beam Relay Control11B2575 00
Headlamp and Panel Dimmer Switch Ground1
LF Headlamp Ground1
RF Headlamp Ground1
Turn Signal/Multifunction Switch Ground1
1. Headlamps Malfunction

When the headlamp switch is placed in the headlamp ON position, ground is applied to the body control module (BCM) through the headlamp low beam signal circuit. The BCM then applies ground to the headlamp 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 LO HDLP fuses to the low beam headlamps.

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

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

The low 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 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 86 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. 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 an open/high resistance.
  5. Disconnect the harness connector at the appropriate headlamp - front.
  6. Test for less than 5 ohms between the headlamp - front ground circuit terminal B and ground If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the headlamp - front.
  8. Connect a 20 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the headlamp - front is activated. If the headlamp - front does not activate and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the headlamp - front. If the headlamp - front does not activate and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the headlamp - front.
  9. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
  10. Command the Low Beams 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 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 BCM.
  11. If all circuits test normal, test or replace the low beam relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Headlamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Replacement (HD Chevrolet Diesel)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__headlamp-replacement-hd-chevrolet-diesel) , «Headlamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__headlamp-replacement-gmc)
  3. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
HDLP LO/HID Relay B+111
HI Beam Relay B+111
Flash to Pass Switch Signal111
Headlamp Switch Headlamps ON SignalB257A 0011
Headlamp Switch Headlamps OFF SignalB257A 0011
Headlamp Switch High Beam Signal111
Headlamp High Beam Relay Control11B2580 00
Headlamp Low Beam Relay Control11B2575 00
Headlamp and Panel Dimmer Switch Ground1
LF Headlamp Ground1
RF Headlamp Ground1
Turn Signal/Multifunction Switch Ground1
1. Headlamps Malfunction

When the headlamp switch is placed in the AUTO position, the body control module (BCM) receives a ground signal through the headlamp switch headlamps OFF signal circuit. The headlamp switch headlamps ON signal circuit and the park lamp switch signal circuit are both open and have no ground signal. When the headlamp switch is placed in the PARK or HEAD position, the BCM will receive a ground signal through the headlamp switch headlamps ON signal circuit and the park lamp switch signal circuit. The headlamp switch headlamps OFF signal circuit will be open and have no ground signal.

Battery voltage must be between 9-16 V.

The BCM detects a short to ground on the headlamp switch headlamps OFF signal circuit or the headlamp switch headlamps ON 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.
  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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 BCM.
  2. Connect a test lamp between B+ and the signal circuit terminal 17.
  3. Turn the headlamp switch between the headlamp AUTO and headlamp OFF positions. The test lamp should turn ON and OFF as the switch is cycled. If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the headlamp switch. If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the headlamp switch.
  4. Connect a test lamp between B+ and the signal circuit terminal 12.
  5. Turn the headlamp switch to the ON and OFF positions. The test lamp should turn ON and OFF as the switch is cycled. If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the headlamp switch. If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the headlamp switch.
  6. If all circuits test normal, replace the BCM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
HDLP LO/HID Relay B+111
HI Beam Relay B+111
Flash to Pass Switch Signal111
Headlamp Switch Headlamps ON SignalB257A 0011
Headlamp Switch Headlamps OFF SignalB257A 0011
Headlamp Switch High Beam Signal111
Headlamp High Beam Relay Control11B2580 00
Headlamp Low Beam Relay Control11B2575 00
Headlamp and Panel Dimmer Switch Ground1
LF Headlamp Ground1
RF Headlamp Ground1
Turn Signal/Multifunction Switch Ground1
1. Headlamps Malfunction

When the turn signal/multifunction switch is placed in the headlamps high or flash to pass (FTP) position, ground is applied to the body control module (BCM) through the headlamp high beam signal circuit or the flash to pass signal circuit. The BCM applies ground to the headlamp 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 HI HEADLAMP fuses to the high beam headlamps.

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

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

The high beam headlamps and flash to pass (FTP) 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 X4 harness connector at the body control module.
  2. Ignition ON, verify the high beam headlamps are OFF. If the high beam headlamps are ON, test the high beam relay control circuit for a short to ground. If the circuit tests normal, replace the fuse block - underhood.
  3. Ignition OFF, connect a 3 A fused jumper between the high beam relay control circuit terminal 16 and ground.
  4. Ignition ON, verify the high beam headlamps are ON. If the high beam headlamps are OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the fuse block - underhood.
  5. If all circuits test normal, replace the body control module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
Park Lamp Relay B+11
Park Lamp Switch ON Signal111
Park Lamp Relay Control11B2585 00
Park Lamp Control111
License Lamp Ground1
Headlamp and Panel Dimmer Switch Ground22
Park Lamps - LF Ground1
Park Lamps - RF Ground1
Tail/Stop and Turn Signal Lamps - LR Ground1
Tail/Stop and Turn Signal Lamps - RR Ground1
Turn Signal/Multifunction Switch Ground1
1. Park, License, and/or Tail Lamps Malfunction 2. Headlamp Switch Malfunction

Battery positive voltage is applied at all times to both the coil and switch sides of the PARK LAMP Relay located in the underhood fuse block. When the headlamp switch is placed in either the HEAD or PARK position, ground is applied to the park lamp signal circuit to the body control module (BCM). The BCM responds by applying ground to the PARK LAMP Relay control circuit. This energizes the PARK LAMP Relay coil causing the relay switch contacts to close allowing B+ to flow through the LT PRK fuse, RT PRK fuse, and the TRLR PRK fuse, to all of the park, tail, license, and marker lamps.

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

The BCM detects a short to voltage in the PARK LAMP Relay control circuit.

The park lamps 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 park lamp 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 85 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. 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 an open/high resistance.
  5. Disconnect the harness connector at the appropriate park lamp.
  6. Test for less than 5 ohms between the ground circuit terminal listed below and ground: Park/Turn Signal Lamp - Terminal G Tail/Stop and Turn Signal Lamp - Terminal GRD License Lamp - Terminal B Rear Fender Clearance Lamp - Terminal B Side Marker Lamp - Terminal A Roof Clearance Lamp - Terminal A Tailgate Marker Lamp - Terminal B If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  7. Connect the harness connector at the park lamp.
  8. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the park lamp is activated. If the park lamp does not activate and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the park lamp. If the park lamp does not activate and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the park lamp.
  9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  10. Command the Parking 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 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 BCM.
  11. If all circuits test normal, replace the park lamp relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Roof Clearance Center Lamp Replacement (U01)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Roof Clearance Outer Lamp Replacement (U01)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  4. «Rear Fender Clearance Lamp Replacement»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  5. «Rear License Plate Lamp Replacement (Silverado GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Rear License Plate Lamp Replacement (VF7)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  6. «Tail Lamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (HD)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  7. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
DRL Relay B+22
Ambient Light Sensor SignalB2645 03B2645 07B2645 07
Daytime Running Lamps Control22B2600 00
Headlamp - Left Front Low Beam Control111
Headlamp - Right Front Low Beam Control111
Ambient Light Sensor GroundB2645 07
Headlamp - Left Front Ground1
Headlamp - Right Front Ground1
1. Headlamps Malfunction 2. Daytime Running Lamps Malfunction

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 V depending on outside lighting conditions. The body control module (BCM) provides a 5 V reference signal to the ambient light sensor. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL relay via the DRL relay control circuit. When the BCM applies ground to the DRL relay control circuit, the DRL relay coil energizes causing the relay switch contacts to close. With the DRL relay switch contacts closed, battery voltage flows through the DRL 1 and DRL 2 fuses to the left and right LO HDLP fuses to the low beam headlamps. The DRL control circuit that supplies the low beam headlamp fuses with voltage contains a loop of wire that acts as resistance. This resistance is responsible for the low beam headlamps illuminating at a reduced intensity. Any function or condition that turns on the headlamps will cancel DRL operation.

  1. Battery voltage must be between 9-16 V.
  2. Headlamp switch in AUTO position.

The BCM detects a short to voltage in the DRL relay control circuit.

The BCM will disable the DRL relay 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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, verify with a scan tool the Park Brake Switch parameter displays Released.

  1. If not the specified value, refer to «Brake Warning Indicator Malfunction»(/gmc/sierra-2500/2012-2012/remont/mechanical-hydraulic/#hydraulic-brake-system) .
  1. Ignition OFF, disconnect the X4 harness connector at the fuse block - underhood.
  2. Connect a test lamp between the control circuit terminal H4 and B+.
  3. Command the DRL 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 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 BCM.
  4. Ignition OFF, connect the X4 harness connector at the fuse block - underhood. Disconnect the harness connector at the headlamp - low beam.
  5. Test for less than 5 ohms between the ground circuit terminal B 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 A and ground.
  7. Command the DRL 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 fuse block - underhood. If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the fuse block - underhood. If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the headlamp - low beam.
  8. If all circuits test normal, test or replace the headlamp - low beam.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Headlamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Replacement (HD Chevrolet Diesel)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__headlamp-replacement-hd-chevrolet-diesel) , «Headlamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__headlamp-replacement-gmc)
  3. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
IS LPS Fuse B+B1395 03B1395 03
Headlamp and Panel Dimmer Switch SignalB1395 0311
I/P Lamps Dimmer Switch SignalB2652 0011
I/P Dimming Voltage ReferenceB1395 0311
Indicator Dimming ControlB2625 0011
LED Backlight Dimming ControlB2610 0011
Headlamp and Panel Dimmer Switch Ground1
1. Interior Backlighting Malfunction

The instrument panel (I/P) lamp dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The I/P dimmer switch provides a voltage signal that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The body control module (BCM) provides a low reference signal and a B+ voltage reference to the I/P dimmer switch. When the I/P dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the I/P dimmer switch through the I/P dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies the dimmed voltage to the I/P lamps supply voltage circuit and the interior backlighting components dim to the requested level.

  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.

The BCM will not dim or illuminate any indicators supplied by the LED backlight dimming 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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

Note. Each back lighted component may need to be disconnected to isolate a short to voltage or short to ground. Use the schematic to identify the following: Back lighted components the vehicle is equipped with. Component locations on the back lighting dimming control circuit Each component's control and ground circuit terminals

  1. Ignition OFF, disconnect the harness connector at any component with inoperative backlighting.
  2. Ignition OFF, scan tool disconnected, interior lamps OFF, doors CLOSED, test for less than 5 ohms between the ground circuit 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 and ground.
  4. Command the Incandescent Dimming Control 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the component with the inoperative backlighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. Refer to the appropriate replacement procedure for the component causing the condition.
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, driver door lock and side window switch, or passenger door lock and side window switch replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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 Voltage SupplyB2615 00B2615 00B2615 00
Courtesy Lamp Ground1
1. Courtesy Lamps Malfunction

Voltage for the courtesy lamps is supplied from body control module (BCM), driver door switch, and passenger door switch. When a door is opened, a signal is applied to the door module. The door module then applies a message on the low speed GMLAN serial data communication circuit to the BCM to activate the courtesy lamps. The BCM then applies voltage to the courtesy lamps voltage supply circuit and the components on that circuit.

The ignition is ON, the BCM, driver door switch, and passenger door switch attempt to illuminate the courtesy lamps.

The BCM, driver door lock and side window switch, or passenger door lock and side window switch detects a short to ground, short to voltage, or open on the courtesy lamp voltage supply circuit.

The BCM, driver door lock and side window switch, and passenger door lock and side window switch cease attempts to illuminate the courtesy lamps.

  1. The conditions for setting the DTC are no longer present.
  2. A history DTC clears after 100 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 Courtesy Lamps ON and OFF with a scan tool. The courtesy lamps should turn ON and OFF when changing between the commanded states.

Note. Each courtesy lighting component may need to be disconnected to isolate a short to voltage or short to ground. Use the schematic to identify the following: Courtesy Lighting components the vehicle is equipped with. Component locations on the courtesy lighting control circuit Each component's control and ground circuit terminals

  1. Ignition OFF, disconnect the harness connector at any component with inoperative courtesy lighting.
  2. Ignition OFF, scan tool disconnected, interior lamps OFF, doors CLOSED, test for less than 5 ohms between the ground circuit 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 and ground.
  4. Command the Courtesy Lamp Control 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the component with the inoperative courtesy lighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. Refer to the appropriate replacement procedure for the component causing the condition.
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, driver door lock and side window switch, or passenger door lock and side window switch replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
IS LPS Fuse B+B1395 03B1395 03
Headlamp and Panel Dimmer Switch SignalB1395 0311
I/P Lamps Dimmer Switch SignalB2652 0011
I/P Dimming Voltage ReferenceB1395 0311
Indicator Dimming ControlB2625 0011
LED Backlight Dimming ControlB2610 0011
Headlamp and Panel Dimmer Switch Ground1
1. Interior Backlighting Malfunction

The instrument panel (I/P) dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The I/P dimmer switch provides a voltage signal that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The body control module (BCM) provides a low reference signal and a B+ voltage reference to the I/P dimmer switch. When the I/P dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the I/P dimmer switch through the I/P dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies the dimmed voltage to the I/P lamps supply voltage circuit and the interior backlighting components dim to the requested level.

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

The BCM detects a short to ground in the LED indicator dimming control circuit.

The BCM will not illuminate the LEDs supplied by the LED indicator dimming 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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, headlamp switch to PARK, vary the interior lamp dimming switch from dim to full bright. The LED lamps should dim and then become full bright.

Note. Each LED dimming lighting component may need to be disconnected to isolate a short to voltage or short to ground. Use the schematic to identify the following: LED dimming lighting components the vehicle is equipped with. Component locations on the LED dimming control circuit Each component's control and ground circuit terminals

  1. Ignition OFF, disconnect the harness connector at any component with inoperative LED dimming lighting.
  2. Ignition OFF, scan tool disconnected, interior lamps OFF, doors CLOSED, test for less than 5 ohms between the ground circuit 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 and ground.
  4. Command the LED Dimming Control 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the component with the inoperative LED dimming lighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. Refer to the appropriate replacement procedure for the component causing the condition.
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
Outside Rearview Mirror Courtesy Lamp Control - Left111
Outside Rearview Mirror Courtesy Lamp Control - Right111
Outside Rearview Mirror Courtesy Lamp Signal - LeftB2635 00B2635 001
Outside Rearview Mirror Courtesy Lamp Signal - RightB2635 00B2635 001
1. Courtesy Lamps Malfunction

The outside rearview mirror courtesy lamps are located on the driver and passenger outside rearview mirrors and are used to illuminate the vehicles entry point. When a door is opened or a lock/unlock request from the key fob is performed, the body control module (BCM) communicates via serial data with the driver and passenger door lock/window switches requesting the outside rearview mirror courtesy lamps be illuminated. The driver and passenger door lock/window switches provide each LED with a voltage signal circuit and when the request to command the LED's ON is received from the BCM, the driver and passenger door lock/window switches respond to the request by switching the control circuit to ground allowing voltage to flow from the signal circuits illuminating each LED located in the lower portion of the driver and passenger outside rearview mirrors.

  1. Battery voltage is between 9 - 16 V.
  2. Ignition ON.

DTC B2635 00

The driver door lock/window switch detects a short to ground or open/high resistance in the outside rearview mirror courtesy lamp signal circuit.

DTC B2635 00

The passenger door lock/window switch detects a short to ground or open/high resistance in the outside rearview mirror courtesy lamp signal circuit.

The driver door lock/window switch and passenger door lock/window switch cease attempts to illuminate the outside rearview mirror courtesy lamp.

  1. The conditions for setting the DTC are no longer present.
  2. A history DTC clears after 100 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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. Disconnect the harness connector at the appropriate outside rearview mirror courtesy lamp.
  2. Ignition ON, verify a test lamp illuminates between the exterior courtesy lamp signal circuit terminal and ground. If the test lamp does not illuminate, test the signal circuit for a short to ground or an open/high resistance.
  3. Connect a test lamp between the control circuit terminal and the signal circuit terminal.
  4. Command the Puddle/Courtesy 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 ground. If the circuit tests normal, replace the appropriate door lock/window switch. 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 appropriate door lock/window switch.
  5. If all circuits test normal, test or replace the inoperative outside rearview mirror courtesy lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Outside Rearview Mirror Courtesy Lamp Replacement»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Door Lock and Side Window Switch Replacement - Driver Side»(/gmc/sierra-2500/2012-2012/remont/door-locks-anti-theft-systems/#power-door-lock-system-and-release-systems)
  3. «Door Lock and Side Window Switch Replacement - Passenger Side»(/gmc/sierra-2500/2012-2012/remont/door-locks-anti-theft-systems/#power-door-lock-system-and-release-systems)
  4. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
DRL Relay B+22
Ambient Light Sensor SignalB2645 03B2645 07B2645 07
Daytime Running Lamps Control22B2600 00
Headlamp - Left Front Low Beam Control111
Headlamp - Right Front Low Beam Control111
Ambient Light Sensor GroundB2645 07
Headlamp - Left Front Ground1
Headlamp - Right Front Ground1
1. Headlamps Malfunction 2. Daytime Running Lamps Malfunction

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a 5 V reference signal to the ambient light sensor. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL relay via the DRL relay control circuit. When the BCM applies ground to the DRL relay control circuit, the DRL relay coil energizes causing the relay switch contacts to close. With the DRL relay switch contacts closed, battery voltage flows through the DRL 1 and DRL 2 fuses to the left and right LO HDLP fuses to the low beam headlamps. The DRL control circuit that supplies the low beam headlamp fuses with voltage contains a loop of wire that acts as resistance. This resistance is responsible for the low beam headlamps illuminating at a reduced intensity. Any function or condition that turns on the headlamps will cancel DRL operation.

Battery voltage must be between 9-16 V.

B2645 03

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

B2645 07

The BCM detects a short to voltage or an open/high resistance in the ambient light sensor signal circuit.

  1. Automatic lamp control (ALC) is 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 ambient light sensor.
  2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 5.0 ohms between the appropriate ground circuit terminal listed below and ground. Terminal B - (C67/C42) Terminal C - (CJ2) If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 4.5 V. If less than the specified range, test the signal circuit terminal listed below for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. Terminal A - (C67/C42) Terminal D - (CJ2)
  4. Install a 3 A fused jumper wire between the signal circuit terminal listed below and ground. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 V. Terminal A - (C67/C42) Terminal D - (CJ2) 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 BCM
  5. If all circuits test normal, replace the ambient light sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Ambient Light Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
IS LPS Fuse B+B1395 03B1395 03
Headlamp and Panel Dimmer Switch SignalB1395 0311
I/P Lamps Dimmer Switch SignalB2652 0011
I/P Dimming Voltage ReferenceB1395 0311
Indicator Dimming ControlB2625 0011
LED Backlight Dimming ControlB2610 0011
Headlamp and Panel Dimmer Switch Ground1
1. Interior Backlighting Malfunction

The instrument panel (I/P) lamp dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The I/P dimmer switch provides a voltage signal that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The body control module (BCM) provides a low reference signal and a B+ voltage reference to the I/P dimmer switch. When the I/P dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the I/P dimmer switch through the I/P dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies the dimmed voltage to the I/P lamps supply voltage circuit and the interior backlighting components dim to the requested level.

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

The BCM detects a short to ground in the I/P lamps dimmer switch signal circuit.

The BCM will not DIM or illuminate any I/P lamps supplied by the I/P lamps dimmer switch signal 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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

Note. Each back lighted component may need to be disconnected to isolate a short to voltage or short to ground. Use the schematic to identify the following: Back lighted components the vehicle is equipped with. Component locations on the back lighting dimming control circuit Each component's control and ground circuit terminals

  1. Ignition OFF, disconnect the harness connector at any component with inoperative backlighting.
  2. Ignition OFF, scan tool disconnected, interior lamps OFF, doors CLOSED, test for less than 5 ohms between the ground circuit 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 and ground.
  4. Command the Incandescent Dimming Control 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the component with the inoperative backlighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. Refer to the appropriate replacement procedure for the component causing the condition.
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
Stop Lamp Relay ControlB3445 0011
Tail/Stop Lamp Control - Left111
Tail/Stop Lamp Control - Right111
Stop Lamp Switch Signal111
Stop Lamp Switch B+ Voltage ReferenceB1395 03, B3600 0311
Stop Lamp Relay Switch B+11
Center High Mounted Stop Lamp (CHMSL) Ground2
Tail/Stop Lamp Ground - Left1
Tail/Stop Lamp Ground - Right1
Stop Lamp Relay Ground1
1. Stop Lamps Malfunction 2. Center High Mounted Stop Lamp (CHMSL) Malfunction

The stop lamp switch is used to sense the action of the driver application of the brake pedal. The body control module (BCM) provides a low reference signal and a B+ reference voltage to the stop lamp switch. When the stop lamp switch contacts close indicating the brakes have been applied, the BCM will apply battery voltage to stop lamp relay control circuit and the center high mounted stop lamp (CHMSL). When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage to the STOP LP fuse to illuminate the left and right stop lamps.

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

The BCM detects a short to ground in the CHMSL control circuit when the stop lamps are being commanded ON.

The BCM will not illuminate the CHMSL.

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

Diagnostic Aids

Note. The stop lamps will not illuminate unless the ignition is in the ON position. For more detailed information concerning stop lamp operation, refer to Exterior Lighting Systems Description and Operation .

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 CHMSL.
  2. Test for less than 5.0 ohms between the ground circuit terminal B 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 A and the ground circuit terminal B.
  4. Ignition ON, turn the stop lamps 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 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 BCM.
  5. If all circuits test normal, replace the CHMSL.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Tail Lamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
IS LPS Fuse B+B1395 03B1395 03
Headlamp and Panel Dimmer Switch SignalB1395 0311
I/P Lamps Dimmer Switch SignalB2652 0011
I/P Dimming Voltage ReferenceB1395 0311
Indicator Dimming ControlB2625 0011
LED Backlight Dimming ControlB2610 0011
Headlamp and Panel Dimmer Switch Ground1
1. Interior Backlighting Malfunction

The instrument panel (I/P) lamp dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The I/P dimmer switch provides a voltage signal that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The body control module (BCM) provides a low reference signal and a B+ voltage reference to the I/P dimmer switch. When the I/P dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the I/P dimmer switch through the I/P dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies the dimmed voltage to the I/P lamps supply voltage circuit and the interior backlighting components dim to the requested level.

Battery voltage must be between 9-16 V.

The BCM detects a short to ground or an open/high resistance in the I/P dimmer switch signal circuit.

  1. The I/P dimmer switch will not operate.
  2. The I/P dimming lamps will not illuminate.
  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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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, headlamp switch to HEAD, vary the interior lamp dimming switch from dim to full bright. The I/P lamps should dim and then become full bright.

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Verify that a test lamp illuminates between the ground circuit terminal 8 and B+. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.1 V. If greater than the specified range, test the signal circuit terminal 13 for a short to voltage. If the circuit tests normal, replace the BCM.
  4. Ignition ON, test for B+ between the I/P dimming voltage reference circuit terminal 15 and ground. If less than the specified value, test the voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal 13 and the voltage reference circuit terminal 15. Verify the scan tool Dimming Control Signal parameter is greater than 2.6 V. If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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 Stop Lamp (CHMSL) Relay ControlB3884 0011
Tail/Stop Lamp Control - Left111
Tail/Stop Lamp Control - Right111
Center High Mounted Stop Lamp (CHMSL) Ground2
Tail/Stop Lamp Ground - Left1
Tail/Stop Lamp Ground - Right1
1. Stop Lamps Malfunction 2. Center High Mounted Stop Lamp (CHMSL) 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, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) control circuit.

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

The BCM detects a short to ground in the CHMSL control circuit when the stop lamps are being commanded ON.

The BCM will not illuminate the CHMSL.

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

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 underhood fuse block.
  2. Connect a test lamp between B+ and the control circuit terminal K6.
  3. Ignition ON, command the stop lamps 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 ground. If the circuit tests normal, replace the 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 BCM.
  4. If all circuits test normal, replace the underhood fuse block

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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 Position Sensor 5 V ReferenceC0277 06, C0890 03C0277 061
Brake Applied SignalC0297 00 and P0571 0033
Brake Position Sensor SignalC0277 06C0277 06C0277 07C0277 09
Center High Mounted Stop Lamp (CHMSL) Relay ControlB3884 0022
Left Rear Stop/Turn Lamp Control111
Right Rear Stop/Turn Lamp Control111
Brake Position Sensor Low ReferenceC0277 071
Center High Mounted Stop Lamp (CHMSL) Ground22
Left Rear Stop/Turn Lamp Ground11
Right Rear Stop/Turn Lamp Ground11
1. Stop Lamps Malfunction 2. Center High Mounted Stop Lamp (CHMSL) Malfunction 3. 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, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) control circuit.

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

DTC C0277 06 will set for the following conditions

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

DTC C0277 07 will set for the following conditions

  1. The BCM detects a short to battery voltage in the brake pedal position sensor signal circuit.
  2. The BCM detects an open/high resistance in the brake pedal position sensor low reference circuit.

C0277 09

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

C0277 4B

The brake pedal position sensor home position is not learned.

  1. The Service Brake Assist indicator is commanded ON.
  2. If the DTC sets while the vehicle is running, the BCM will activate the brake lights when the vehicles transmission is not in the PARK position and the vehicle is not accelerating.
  3. 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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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

C0277 06 and C0277 07, C0890 03, and C0890 07

  1. Ignition OFF, disconnect the harness connector at the brake pedal position sensor.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the low reference circuit terminal 2. If the test lamp does not illuminate, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  3. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal 1 and ground. If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool BPP Sensor parameter is less than 100 counts. If greater than the specified range, test the signal circuit terminal 3 for a short to voltage. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the 5 V reference circuit terminal 1. Verify the scan tool BPP Sensor parameter is greater than 400 counts. If less than the specified range, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, replace the brake pedal position sensor.

C0277 09

  1. Replace the brake pedal position sensor.
  2. Perform the brake pedal position sensor recalibration procedure. Refer to «Brake Pedal Position Sensor Calibration»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-calibration) .
  3. Operate the vehicle within the Conditions for Running and Setting the DTC and verify the DTC does not reset. If the DTC resets, replace the BCM.

C0277 4B

  1. Verify that the DTC sets under the Conditions for Running and Setting.
  2. Perform the brake pedal position sensor recalibration procedure. Refer to «Brake Pedal Position Sensor Calibration»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-calibration) .
  3. Operate the vehicle within the conditions that the customer experienced and verify the DTC does not reset. If the DTC resets, replace the brake pedal position sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Brake Pedal Position Sensor Replacement (Without JF4)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-replacement-without) , «Brake Pedal Position Sensor Replacement (With JF4)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-replacement-with)
  2. «Brake Pedal Position Sensor Calibration»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-calibration)
  3. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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 Position Sensor 5 V ReferenceC0277 06, C0890 03C0277 061
Brake Applied Signal Terminal 6 X5C0297 00 and P0571 0033
Brake Position Sensor SignalC0277 06C0277 06C0277 07C0277 09
Center High Mounted Stop Lamp (CHMSL) Relay ControlB3884 0022
Left Rear Stop/Turn Lamp Control111
Right Rear Stop/Turn Lamp Control111
Brake Position Sensor Low ReferenceC0277 071
Center High Mounted Stop Lamp (CHMSL) Ground22
Left Rear Stop/Turn Lamp Ground11
Right Rear Stop/Turn Lamp Ground11
1. Stop Lamps Malfunction 2. Center High Mounted Stop Lamp (CHMSL) Malfunction 3. 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, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) control circuit.

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

The BCM detects a short to ground in the brake applied signal circuit.

  1. The BCM stores the DTC to memory.
  2. The Service Brake Assist indicator is commanded ON.
  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.

Note. The stop lamps will not illuminate unless the ignition is in the ON position. For more detailed information concerning stop lamp operation, refer to Exterior Lighting Systems Description and Operation .

Verify that the brake pedal position sensor is properly calibrated.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 ECM.
  2. Connect a test lamp between the appropriate signal circuit terminal listed below and ground: Terminal 7 - with HP2 Terminal 9 - with L20/L9H/LC9/LMG/LGH/LML without HP2 Terminal 33 - with L96 Terminal 55 - with LU3
  3. Ignition ON, turn the stop lamps 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 signal circuit for a short to voltage. If the circuit tests normal, replace the BCM. If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. If all circuits test normal, replace the ECM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Brake Pedal Position Sensor Calibration»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-calibration)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or ECM replacement, setup, and programming

Symptoms - Lighting

  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) , before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
  2. Review the system operation in order to familiarize yourself with the system functions. Refer to the following: «Exterior Lighting Systems Description and Operation»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) «Interior Lighting Systems Description and Operation»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)

Visual/Physical Inspection

  1. Inspect for aftermarket devices which could affect the operation of the Lighting System. Refer to «Checking Aftermarket Accessories»(/gmc/sierra-2500/2012-2012/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

Faulty electrical connections or wiring may be the cause of intermittent conditions. 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. «Backup Lamps Malfunction (Manual Transmission)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Backup Lamps Malfunction (Automatic Transmission)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Courtesy Lamps Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Daytime Running Lamps Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  4. «Door Sill Illumination Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  5. «Front Fog Lamps Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  6. «Hazard Lamps Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  7. «Headlamps Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  8. «Interior Backlighting Malfunction (w/AN3)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Interior Backlighting Malfunction (w/o AN3)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  9. «Park, License, and/or Tail Lamps Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  10. «Stop Lamps Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  11. «Turn Signal Lamps and/or Indicators Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
Backup Lamp Relay B+11
Backup Lamp Switch Signal111
Backup Lamp Relay ControlB2545 0011
Backup Lamps Control111
Backup Lamp - Left Ground1
Backup Lamp - Right Ground1
Backup Lamp Switch Ground1
1. Backup Lamps Malfunction

When the transmission is placed 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 voltage to the backup lamp relay control circuit energizing the backup lamp relay coil. With the relay coil energized, the switch contacts close allowing battery voltage to flow through the VEH BCK/UP fuse to the left and right backup lamps. The BCM also supplies voltage the to inside rearview mirror via the backup lamp relay control circuit for automatic day/night operation. Once the driver moves the gear selector out of the REVERSE position, a serial data message is sent by the TCM requesting the BCM to remove voltage from the backup lamp control circuit. The engine may need to be running for the backup lamps to function.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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, engine running, command the Backup Lamps ON and OFF with a scan tool. The backup lamps should turn ON and OFF when changing between the commanded states.

  1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
  2. Ignition OFF, exterior lamps OFF, test for less that 5.0 ohms between the ground circuit terminal N5 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect the X2 harness connector at the underhood fuse block. Disconnect the X5 harness connector at the underhood fuse block.
  4. Connect a test lamp between the control circuit terminal H8 and ground.
  5. Command the Backup 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 voltage. If the circuit tests normal, replace the 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 BCM.
  6. Ignition OFF, connect the X5 harness connector at the underhood fuse block. Disconnect the harness connector at the appropriate backup lamp.
  7. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal GRD and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  8. Connect a test lamp between the control circuit terminal MJR and ground.
  9. Command the Backup 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 voltage. If the circuit tests normal, replace the underhood fuse block. If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block. If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the underhood fuse block.
  10. If all circuits test normal, replace the backup lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Backup Lamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Backup Lamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  3. «Tail Lamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (HD)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  4. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
Backup Lamp Relay B+11
Backup Lamp Switch Signal222
Backup Lamp Relay ControlB2545 0011
Backup Lamps Control111
Backup Lamp - Left Ground1
Backup Lamp - Right Ground1
Backup Lamp Switch Ground2
1. Backup Lamps Malfunction 2. Backup Lamp Switch Malfunction

When the transmission is placed in the REVERSE position, the backup lamp switch contacts close supplying ground to the engine control module (ECM) via the backup lamp switch signal circuit. The ECM responds by sending a serial data message to the body control module (BCM) indicating the gear selector is in the REVERSE position. The BCM applies voltage to the backup lamp relay control circuit energizing the backup lamp relay coil. With the relay coil energized, the switch contacts close allowing battery voltage to flow through the VEH BCK/UP fuse to the left and right backup lamps. The BCM also supplies voltage the to inside rearview mirror via the backup lamp relay control circuit for automatic day/night operation. Once the driver moves the gear selector out of the REVERSE position, the backup lamp switch contacts open and a serial data message is sent by the ECM requesting the BCM to remove voltage from the backup lamp relay control circuit.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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, engine running, observe the Backup Lamps parameter while shifting the vehicle between the park and reverse gears. The reading should change between ON and OFF when changing between the selected states. If the reading does not change between the specified values, refer to Backup Lamp Switch Malfunction below.
  2. Command the Backup Lamps ON and OFF with a scan tool. The backup lamps should turn ON and OFF when changing between the commanded states. If the backup lamps do not turn ON and OFF when changing between the commanded states, refer to Backup Lamps Malfunction below.

Backup Lamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the backup lamp switch.
  2. Ignition OFF, exterior lamps OFF, test for less that 5.0 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. Ignition ON, verify the backup lamps are not illuminated. If the backup lamps are illuminated, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the ECM.
  4. Install a 3 A fused jumper wire between the signal circuit terminal B and ground. Verify the backup lamps are illuminated. If the backup lamps do not illuminate, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  5. If all circuits test normal, replace the backup lamp switch.

Backup Lamps Malfunction

  1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
  2. Ignition OFF, exterior lamps OFF, test for less that 5.0 ohms between the ground circuit terminal N5 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect the X2 harness connector at the underhood fuse block. Disconnect the X5 harness connector at the underhood fuse block.
  4. Connect a test lamp between the control circuit terminal H8 and ground.
  5. Command the Backup 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 voltage. If the circuit tests normal, replace the 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 BCM.
  6. Ignition OFF, connect the X5 harness connector at the underhood fuse block. Disconnect the harness connector at the appropriate backup lamp.
  7. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal GRD and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  8. Connect a test lamp between the control circuit terminal MJR and ground.
  9. Command the Backup 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 voltage. If the circuit tests normal, replace the underhood fuse block. If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block. If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the underhood fuse block.
  10. If all circuits test normal, replace the backup lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Tail Lamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (HD)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Backup Lamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Backup Lamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  4. «Backup Lamp Switch Replacement»(/gmc/sierra-2500/2012-2012/remont/manual-trans/#manual-transmission-tremec-5-speed-tz0)
  5. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or ECM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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/Reading Lamp Supply Voltage11
Exterior Lamps Illumination Supply Voltage555
I/P Dimming VoltageB1395 03B1395 03B1395 07
Dome Lamp Switch Signal222
Left Front Door Open Switch Signal333
Left Rear Door Open Switch Signal444
Right Front Door Open Switch Signal333
Right Rear Door Open Switch Signal444
Dome/Reading Lamp ControlB2615 00B2615 00
Dome/Reading Lamp Low Control - Driver Door1
Dome/Reading Lamp Low Control - Passenger Door1
Inadvertent Power Control555
Exterior Lamps Low Reference5
I/P Dimmer Switch Ground2
LH Vanity Mirror Courtesy Lamp Ground1
Overhead Console Courtesy Lamp Ground1
Rear Dome Lamp Ground1
RH Vanity Mirror Courtesy Lamp Ground1
1. Courtesy Lamps Malfunction 2. Dome Lamp Switch Malfunction 3. Door Open Switch Malfunction - Front 4. Door Open Switch Malfunction - Rear 5. Exterior Lamps Malfunction

Voltage for the courtesy lamps is supplied from body control module (BCM), driver door switch, and passenger door switch. When a door is opened, a signal is applied to the door module. The door module then applies a message on the low speed GMLAN serial data communication circuit to the BCM to activate the courtesy lamps. The BCM then applies voltage to the courtesy lamps voltage supply circuit and the components on that circuit.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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. Command the Courtesy Lamps ON and OFF with a scan tool. The courtesy lamps should turn ON and OFF when changing between the commanded states. If the courtesy lamps do not turn ON and OFF when commanded, refer to Courtesy Lamp Malfunction below.
  2. Observe the scan tool Driver Door Switch, Driver Door Ajar Sw. parameter while opening and closing the driver door. The reading should change between Active and Inactive. If the Driver Door Ajar Sw. parameter does not change between Active and Inactive, refer to Door Open Switch Malfunction - Front below.
  3. Observe the scan tool Passenger Door Switch, Passenger Door Ajar Sw. parameter while opening and closing the front passenger door. The reading should change between Active and Inactive. If the Passenger Door Ajar Sw. parameter does not change between Active and Inactive, refer to Door Open Switch Malfunction - Front below.
  4. Observe the scan tool Ctsy. Lamp Actv. Reason parameter while opening and closing each rear door one at a time. The reading should change between Door Open and Door Closed If the Ctsy. Lamp Actv. Reason parameter does not change between Door Open and Door Closed, refer to Door Open Switch Malfunction - Rear below.
  5. All doors closed, observe the scan tool Ctsy. Lamp Actv. Reason parameter while turning the dome lamp switch ON and OFF. The reading should change between Off and Manual. If the Ctsy. Lamp Actv. Reason parameter does not change between Off and Manual, refer to Dome/Interior Lamp Switch Malfunction below.
  6. All doors closed, observe the scan tool Ctsy. Lamp Actv. Reason parameter while turning the interior lamp defeat switch ON and OFF. The reading should change between Off and Manual Defeat. If the Ctsy. Lamp Actv. Reason parameter does not change between Off and Manual, refer to Dome/Interior Lamp Switch Malfunction below.
  7. Turn the individual reading lamps ON and OFF with their respective switches. The reading lamps should turn ON and OFF when changing between the selected states. If any reading lamp does not turn ON and OFF when selected, refer to Reading Lamps Malfunction below.
  8. Turn the left and right vanity mirror lamps ON and OFF with their respective switches. The vanity mirror lamps should turn ON and OFF when changing between the selected states. If any reading lamp does not turn ON and OFF when selected, refer to Vanity Mirror Lighting Malfunction below.
  9. Command the Courtesy Lamp ON and OFF with a scan tool. Verify the exterior illumination lamps turn ON and OFF. If the exterior illumination lamps do not change between ON and OFF, refer to Outside Rearview Mirror Illumination Malfunction below.

Courtesy Lamp Malfunction

  1. Ignition OFF, disconnect the harness connector at the appropriate courtesy lamp.
  2. Test for less than 5 ohms between the ground circuit terminal 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 and the ground circuit terminal.
  4. Ignition ON, command the Courtesy Lamps ON and OFF with the scan tool. The test lamp should turn ON and OFF. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the 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 BCM.
  5. If all circuits test normal, replace the courtesy lamp.

Door Open Switch Malfunction - Front w/AN3

  1. Ignition OFF, disconnect the harness connector at the door latch assembly.
  2. Test for less than 10.0 ohms between the ground circuit terminal listed below and ground. Driver door latch - terminal 8 Passenger door latch - terminal 3 If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Door Ajar Switch parameter is INACTIVE. If the scan tool displays ACTIVE, test the signal circuit terminal listed below for a short to ground. If the circuit tests normal, replace the door control module. Driver door open switch - terminal 6 Passenger door open switch - terminal 1
  4. Install a 3 A fused jumper wire between the signal circuit terminal listed below and ground. Verify the scan tool Door Open Switch parameter is ACTIVE. Driver door open switch - terminal 6 Passenger door open switch - terminal 1 If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the door control module.
  5. If all circuits test normal, replace the door latch assembly.

Door Open Switch Malfunction - Front w/o AN3

  1. Ignition OFF, disconnect the harness connector at the door latch assembly.
  2. Test for less than 10.0 ohms between the ground circuit terminal listed below and ground. Terminal 8 (with AU3) Terminal 6 (without AU3) If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Door Ajar Switch parameter is INACTIVE. If the scan tool displays ACTIVE, test the signal circuit terminal 9 for a short to ground. If the circuit tests normal, replace the BCM.
  4. Install a 3 A fused jumper wire between signal circuit terminal 9 and ground. Verify the scan tool Door Ajar Switch parameter is ACTIVE. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, replace the door latch assembly.

Door Open Switch Malfunction - Rear

  1. Ignition OFF, disconnect the harness connector at the rear door latch assembly.
  2. Interior lamps OFF, test for less than 10.0 ohms between the ground circuit terminal listed below and ground. Left rear door latch assembly - terminal 6 Right rear door latch assembly - terminal 3 If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp illuminates between the door open switch signal circuit terminal listed below and ground. Left rear door open switch - terminal 4 Right rear door open switch - terminal 1 If the test lamp does not illuminate, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. Install a 3 A fused jumper wire between the signal circuit terminal listed below and ground. Verify the courtesy lamps illuminate and remain illuminated. Left rear door open switch - terminal 4 Right rear door open switch - terminal 1 If the courtesy lamps do not remain illuminated, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, replace the rear door latch assembly.

Dome/Interior Lamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Test for less than 5 ohms between the ground circuit terminal 8 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Ctsy. Lamp Actv. Reason parameter is Off. If the scan tool parameter is Manual or Manual Defeat, test the signal circuit terminal listed below for a short to ground. If the circuit tests normal, replace the BCM. Manual terminal 12 Manual Defeat terminal 9
  4. Install a 3 A fused jumper wire between the signal circuit terminal 12 and the ground circuit terminal 8. Verify the scan tool Ctsy. Lamp Actv. Reason parameter is Manual. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal 9 and the ground circuit terminal 8. Verify the scan tool Ctsy. Lamp Actv. Reason parameter is Manual Defeat. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Reading Lamps Malfunction

  1. Ignition OFF, disconnect the X2 harness connector at the BCM.
  2. Verify a test lamp illuminates between the IS LPS fuse B+ circuit terminal 1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. Reconnect the X2 harness connector at the BCM.
  4. Disconnect the harness connector at the appropriate courtesy/reading lamp assembly.
  5. Scan tool OFF, doors CLOSED, interior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  6. Verify a test lamp illuminates between the control circuit terminal C 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, replace the BCM.
  7. Remove the IS LPS fuse and verify the test lamp turns OFF. If the test lamp remains illuminated, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  8. If all circuits test normal, replace the courtesy/reading lamp assembly.

Vanity Mirror Lighting Malfunction

  1. Ignition OFF, disconnect the harness connector at the appropriate vanity mirror lamp.
  2. Test for less than 5 ohms between the ground circuit terminal B 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 signal circuit terminal A and ground. If the test lamp does not illuminate, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  4. Connect the harness connector at the vanity mirror lamp.
  5. Remove the IS LPS fuse and verify the test lamp turns OFF. If the test lamp remains illuminated, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, replace the vanity mirror lamp.

Outside Rearview Mirror Illumination Malfunction

  1. Disconnect the harness connector at the appropriate exterior illumination lamp.
  2. Ignition ON, verify that a test lamp illuminates between the exterior illumination lamp supply circuit terminal and ground. If the test lamp does not illuminate, test the exterior illumination lamp supply circuit for a short to ground or an open/high resistance.
  3. Connect a test lamp between the low side control circuit terminal and the exterior illumination lamp supply circuit terminal.
  4. Command the Puddle/Courtesy 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 ground. If the circuit tests normal, replace the inoperative door switch. 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 inoperative door switch.
  5. If all circuits test normal, test or replace the exterior illumination lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Dome Lamp Replacement»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Outside Rearview Mirror Courtesy Lamp Replacement»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  4. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, driver door switch, or passenger door switch replacement, programming, and setup
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
DRL Relay B+22
Ambient Light Sensor SignalB2645 03B2645 07B2645 07
Daytime Running Lamps Control22B2600 00
Headlamp - Left Front Low Beam Control111
Headlamp - Right Front Low Beam Control111
Ambient Light Sensor GroundB2645 07
Headlamp - Left Front Ground1
Headlamp - Right Front Ground1
1. Headlamps Malfunction 2. Daytime Running Lamps Malfunction

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a 5 V reference signal to the ambient light sensor. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL relay via the DRL relay control circuit. When the BCM applies ground to the DRL relay control circuit, the DRL relay coil energizes causing the relay switch contacts to close. With the DRL relay switch contacts closed, battery voltage flows through the DRL 1 and DRL 2 fuses to the left and right LO HDLP fuses to the low beam headlamps. The DRL control circuit that supplies the low beam headlamp fuses with voltage contains a loop of wire that acts as resistance. This resistance is responsible for the low beam headlamps illuminating at a reduced intensity. Any function or condition that turns on the headlamps will cancel DRL operation.

The DRL will only operate while the engine is running, for automatic transmission, the gear selector is not in the PARK position, the headlamp switch is in the AUTO position, and for manual transmission, the park brake is released

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 OFF, command the Low Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when changing between the commanded states. If the low beam headlamps do not change between the commanded states, refer to «Headlamps Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) .
  2. Command the DRLs ON and OFF with a scan tool. The daytime running lamps should turn ON and OFF when changing between the commanded states. If the daytime running lamps do not change between the commanded states, refer to Daytime Running Lamps Malfunction below.
  3. Observe the scan tool Ambient Light Status parameter while supplying sufficient light to simulate daylight conditions to the ambient light sensor. After 30 seconds, the parameter should be Day. If not the specified value, refer to Ambient Light Sensor Malfunction below.

Daytime Running Lamps Malfunction

  1. Ignition OFF, disconnect the X4 harness connector at the underhood fuse block.
  2. Connect a test lamp between the control circuit terminal H4 and B+.
  3. Command the DRL 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 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 BCM.
  4. Ignition OFF, connect the X4 harness connector at the underhood fuse block.
  5. Remove the DRL 2 fuse from the underhood fuse block.
  6. Connect a test lamp between the relay control circuit of the DRL 2 fuse and ground.
  7. Command the DRL 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 terminal A3 X1 for a short to voltage. If the circuit tests normal, replace the underhood fuse block. If the test lamp is always OFF, test the control circuit terminal A3 X1 for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
  8. If all circuits test normal, replace the underhood fuse block.

Ambient Light Sensor Malfunction

  1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
  2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 5.0 ohms between the ground circuit terminal listed below and ground. Terminal B - (C67/C42) Terminal C - (CJ2) If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 4.5 V. If less than the specified range, test the signal circuit terminal listed below for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. Terminal A - (C67/C42) Terminal D - (CJ2)
  4. Install a 3 A fused jumper wire between the signal circuit terminal listed below and ground. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 V. Terminal A - (C67/C42) Terminal D - (CJ2) 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 BCM
  5. If all circuits test normal, replace the ambient light sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Ambient Light Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  3. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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 00B2615 001
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»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) .
  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.

Control Module References for BCM replacement, setup, and programming

  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
Fog Lamp Relay B+11
Fog Lamp Switch Signal222
Fog Lamp Relay Control11B2530 00
Fog Lamp Control111
Fog Lamp - LF Ground1
Fog Lamp - RF Ground1
Fog Lamp Switch Ground2
1. Fog Lamps Malfunction 2. Fog Lamp Switch Malfunction

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

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 scan tool Front Fog Lamp Switch parameter while activating the front fog lamp switch. The parameter should change between Active and Inactive. If the parameter does not change between the selected states, refer to Fog Lamp Switch Malfunction below.
  2. Turn the front fog lamps ON and OFF with the front fog lamps switch. The front fog lamps should turn ON and OFF as selected. If the front fog lamps do not change between the selected states, refer to Fog Lamps Malfunction below.
  3. Command the Lamp Test ON and OFF with a scan tool. The front fog lamps indicator should turn ON and OFF when changing between the commanded states. If the front fog lamps indicator illuminates during the test, replace the BCM. If the front fog lamps indicator does not illuminate during the test or remains illuminated at all times, replace the instrument cluster.

Fog Lamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Verify that a test lamp illuminates between B+ and the ground circuit terminal 8. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Front Fog Lamp Switch parameter is Inactive. If not the specified value, test the signal circuit terminal 10 for a short to ground. If the circuit tests normal, replace the BCM.
  4. Install a 3 A fused jumper wire between the signal circuit terminal 10 and the ground circuit terminal 8. Verify the scan tool Front Fog Lamp Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Fog Lamps Malfunction

  1. Ignition OFF, disconnect the fog lamp 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 resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground. If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  5. Ignition OFF, disconnect the harness connector at the appropriate fog lamp.
  6. Test for less than 5.0 ohms between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the fog lamp.
  8. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the fog lamps are activated. If the fog lamps do not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the fog lamp.
  9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  10. Command the Fog 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 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 BCM.
  11. If all circuits test normal, test or replace the fog lamp relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Fog Lamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__fog-lamp-switch-replacement-with-rpo) , «Fog Lamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__fog-lamp-switch-replacement-without-rpo)
  2. «Front Fog Lamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Front Fog Lamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  4. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  5. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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 Switch Signal111
Turn Signal/Multifunction Switch Ground1
1. Hazard Lamps Malfunction

The hazard flashers may be activated in any power mode. The hazard switch is located on the turn signal/multifunction switch and is permanently grounded. When the hazard switch is placed in the ON position, ground is applied through the hazard switch signal circuit to the body control module (BCM). The BCM supplies battery voltage to all four turn signal lamps in an ON and OFF duty cycle. When the hazard switch is activated, the BCM sends a serial data message to the instrument panel cluster (IPC) requesting both turn signal indicators to be cycled ON and OFF.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 scan tool Hazard Lamp Switch parameter while turning the hazard lamp switch ON and OFF. The reading should change between Active and Inactive. If the parameter does not change between the commanded states, refer to the Circuit/System Testing below.
  2. Observe the right and left turn signal lamps while turning the hazard lamp switch ON and OFF. The right and left turn signal lamps should flash ON and OFF while the hazard lamp switch is ON and remain OFF when the hazard lamp switch is OFF. If the turn signal lamps do not cycle between the selected states, refer to «Turn Signal Lamps and/or Indicators Malfunction»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) .
  3. Command the Lamp Test ON and OFF with a scan tool. The left and right turn signal indicators should turn ON and OFF when changing between the commanded states. If the left and right turn signal indicators illuminate during the test, replace the BCM. If the left and right turn signal indicators do not illuminate during the test or remain illuminated at all times, replace the instrument cluster.
  1. Ignition OFF, disconnect the X1 harness connector at the turn signal/multifunction switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal C. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Hazard Lamp Switch parameter is Inactive. If not the specified value, test the signal circuit terminal G for a short to ground. If the circuit tests normal, replace the BCM.
  4. Install a 3 A fused jumper wire between the signal circuit terminal G and ground. Verify the scan tool Hazard Lamp Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the turn signal/multifunction switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Turn Signal Multifunction Switch Replacement»(/gmc/sierra-2500/2012-2012/remont/steering-column-switches/#steering-wheel-and-steering-column)
  2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or IPC replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
HDLP LO/HID Relay B+222
HI Beam Relay B+333
Flash to Pass Switch Signal444
Headlamp Switch Headlamps ON SignalB257A 0011
Headlamp Switch Headlamps OFF SignalB257A 0011
Headlamp Switch High Beam Signal444
Headlamp High Beam Relay Control33B2580 00
Headlamp Low Beam Relay Control22B2575 00
Headlamp and Panel Dimmer Switch Ground1
LF Headlamp Ground2
RF Headlamp Ground2
Turn Signal/Multifunction Switch Ground1
1. Headlamp Switch Malfunction 2. Headlamps Malfunction - Low Beam 3. Headlamps Malfunction - High Beam 4. Headlamp Dimmer Switch Malfunction

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the headlamp switch. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil is supplied with ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery voltage to the relay coil and switch circuits. The low beam headlamps operate when the BCM grounds the relay coil control circuit to the relay coil of the low beam headlamp relay. This energizes the low beam relay causing the switch contacts to close. With the switch contacts closed, battery voltage is applied to the LT-LO HDLP and RT-LO HDLP beam fuses through to the left and right low beam headlamps. When the headlamp high beam relay coil is energized, current flows through the LT-HI HEADLAMP and the RT-HI HEADLAMP fuses to the high beam headlamps. With the headlamp dimmer switch in the high beam position the BCM sends a serial data message to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 scan tool Headlamp Switch parameter while turning the headlamp switch ON and OFF. The reading should change between Active and Inactive. If the reading does not change between the selected states, refer to Headlamp Switch Malfunction below.
  2. Observe the scan tool Auto Hdlp. Disable Sw. parameter while turning the headlamp switch ON and OFF. The reading should toggle between Active and Inactive. If the reading does not change between the selected states, refer to Headlamp Switch Malfunction below.
  3. Observe the scan tool Flash to Pass Switch parameter while applying and releasing the turn signal/multifunction switch. The reading should toggle between Active and Inactive. If the reading does not change between the selected states, refer to Turn Signal/Multifunction Switch Malfunction below.
  4. Observe the scan tool High Beam Select Switch parameter while applying and releasing the high beam select switch. The reading should toggle between Active and Inactive. If the reading does not change between the selected states, refer to Turn Signal/Multifunction Switch Malfunction below.
  5. Command the Low Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when commanded. If the low beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction - Low Beam below.
  6. Command the High Beams ON and OFF with a scan tool. The high beam headlamps should turn ON and OFF when commanded. If the high beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction - High Beam below.
  7. Command the Lamp Test ON and OFF with a scan tool. The high beam indicator should turn ON and OFF when changing between the commanded states. If the high beam indicator illuminates during the test, replace the BCM. If the high beam indicator does not illuminate during the test or remain illuminated at all times, replace the instrument cluster.

Headlamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Verify that a test lamp illuminates between B+ and the ground circuit terminal 8. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Headlamp Switch parameter is Inactive. If not the specified value, test the signal circuit terminal 1 for short to ground. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool Auto Hdlp. Disable Sw. parameter is Inactive. If not the specified value, test the signal circuit terminal 3 for short to ground. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool Headlamp Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. Install a 3 A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool Auto Hdlp. Disable Sw. parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, disconnect the X2 harness connector at the turn signal/multifunction switch.
  2. Verify that a test lamp illuminates between B+ and the ground circuit terminal D. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Verify the scan tool High Beam Select switch parameter is Inactive. If not the specified value, test the signal circuit terminal E for a short to ground. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool Flash to Pass Switch parameter is Inactive. If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool High Beam Select Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. Install a 3 A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Flash to Pass Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the signal/multifunction switch.

Headlamps Malfunction - Low Beam

  1. Ignition OFF, disconnect the 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 86 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. 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 an open/high resistance.
  5. Disconnect the harness connector at the appropriate headlamp - low beam.
  6. Test for less than 5 ohms between the headlamp - low beam ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the headlamp - low beam.
  8. Connect a 20 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the headlamp - low beam is activated. If the headlamp - low beam does not activate and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the headlamp - low beam. If the headlamp - low beam does not activate and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the headlamp - low beam.
  9. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
  10. Command the Low Beams 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 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 BCM.
  11. If all circuits test normal, test or replace the low beam relay.

Headlamps Malfunction - High Beam

  1. Ignition OFF, disconnect the X4 harness connector at the body control module.
  2. Ignition ON, verify the high beam headlamps are OFF. If the high beam headlamps are ON, test the high beam relay control circuit for a short to ground. If the circuit tests normal, replace the fuse block - underhood.
  3. Ignition OFF, connect a 3 A fused jumper between the high beam relay control circuit terminal 16 and ground.
  4. Ignition ON, verify the high beam headlamps are ON. If the high beam headlamps are OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the fuse block - underhood.
  5. Ignition OFF, connect the X4 harness connector at the body control module. Disconnect the harness connector at the appropriate high beam headlamp.
  6. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5.0 ohms between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect a test lamp between the control circuit terminal A and ground.
  8. Command the High Beams 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 fuse block-underhood. If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the fuse block-underhood. If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the high beam headlamp.
  9. If all circuits test normal, replace the high beam headlamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Headlamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Replacement (HD Chevrolet Diesel)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__headlamp-replacement-hd-chevrolet-diesel) , «Headlamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__headlamp-replacement-gmc)
  3. «Headlamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  4. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  5. «Underhood Electrical Center or Junction Block Replacement»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  6. «Turn Signal Multifunction Switch Replacement»(/gmc/sierra-2500/2012-2012/remont/steering-column-switches/#steering-wheel-and-steering-column)
  7. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or instrument panel replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
IS LPS fuse B+B1395 03B1395 03
I/P Dimmer Switch SignalB1395 0311
I/P Lamps Dimmer Switch SignalB2652 0022
I/P Dimming Voltage ReferenceB1395 0311
Indicator Dimming ControlB2625 0033
LED Backlight Dimming ControlB2610 0033
I/P Dimmer Switch Ground1
1. Dimmer Switch Malfunction 2. Interior Backlighting Malfunction - Incandescent 3. Interior Backlighting Malfunction - LED

When the ignition switch is turned to the RUN position, the radio VF display turns ON at maximum brightness. When the park lamps are ON, all incandescent and LED back lighting turn ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time all VF displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the body control module (BCM). When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. When the I/P dimmer switch is moved from MIN to MAX, all VF displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 driver door switch while commanding the Driver Door Switch Integrated Sw. Backlighting Test ON and OFF with a scan tool. The switch backlighting should turn ON and OFF when changing between the commanded states. If the backlighting does not turn ON and OFF, replace the driver door lock and side window switch.
  2. Observe the passenger door switch while commanding the Passenger Door Switch Integrated Sw. Backlighting Test ON and OFF with a scan tool. The switch backlighting should turn ON and OFF when changing between the commanded states. If the backlighting does not turn ON and OFF, replace the passenger door lock and side window switch.
  3. Observe the driver memory/heated seat switch while commanding the Driver Door Switch Non-Integrated Backlighting Test ON and OFF with a scan tool. The switch backlighting should turn ON and OFF when changing between the commanded states. If the backlighting does not turn ON and OFF, refer to Front Door Switch Backlighting Malfunction below.
  4. Observe the passenger heated seat switch while commanding the Passenger Door Switch Non-Integrated Backlighting Test ON and OFF with a scan tool. The switch backlighting should turn ON and OFF when changing between the commanded states. If the backlighting does not turn ON and OFF, refer to Front Door Switch Backlighting Malfunction below.
  5. Observe the scan tool Dimming Control Signal parameter while operating the dimmer switch from high to low. The reading should change from a high percent to a low percent as the switch is rotated. If the reading does not change between the selected states, refer to Dimmer Switch Malfunction below.
  6. Observe the function of the backlighting components while commanding the LED Dimming or Incandescent Dimming ON and OFF with a scan tool. The backlighting components should turn ON and OFF while changing between the commanded states. If the backlighting components do not turn ON and OFF, refer to Interior Backlighting Malfunction below.

Front Door Switch Backlighting Malfunction

  1. Ignition OFF, disconnect the harness connector X4 at the door lock and side window switch.
  2. Connect a 3 A fused jumper wire between the low reference circuit terminal 4 and ground.
  3. Connect a test lamp between the backlight supply voltage circuit terminal 13 and B+. The heated seat switch backlighting should illuminate. If the switch backlighting does not illuminate, replace the heated seat switch.
  4. If the switch backlighting tests normal, replace the door lock and side window switch.

Dimmer Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Verify that a test lamp illuminates between the ground circuit terminal 8 and B+. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.1 V. If greater than the specified range, test the signal circuit terminal 13 for a short to voltage. If the circuit tests normal, replace the BCM.
  4. Ignition ON, test for B+ between the I/P dimming voltage reference circuit terminal 15 and ground. If less than the specified value, test the voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal 13 and the voltage reference circuit terminal 15. Verify the scan tool BCM Dimming Control Signal parameter is greater than 2.6 V. If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Interior Backlighting Malfunction

  1. Ignition OFF, disconnect the harness connector at any component with inoperative backlighting.
  2. Ignition OFF, scan tool disconnected, interior lamps OFF, doors CLOSED, test for less than 5 ohms between the ground circuit 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 and ground.
  4. Command the LED Dimming or Incandescent Dimming 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, replace the component with inoperative backlighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Front Seat Heater Switch Replacement»(/gmc/sierra-2500/2012-2012/remont/seats/#seat-heating-system-and-seat-cooling-system)
  2. «Door Lock and Side Window Switch Replacement - Driver Side»(/gmc/sierra-2500/2012-2012/remont/door-locks-anti-theft-systems/#power-door-lock-system-and-release-systems)
  3. «Door Lock and Side Window Switch Replacement - Passenger Side»(/gmc/sierra-2500/2012-2012/remont/door-locks-anti-theft-systems/#power-door-lock-system-and-release-systems)
  4. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  5. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, door lock and side window switch, IPC, radio, HVAC control module, and rear seat audio controller replacement, programming, and setup.
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
IS LPS Fuse B+ SupplyB1395 03B1395 03
I/P Dimmer Switch SignalB1395 0311
I/P Lamps Dimmer Switch SignalB2652 0022
I/P Dimming Voltage ReferenceB1395 0311
Indicator Dimming ControlB2625 0033
LED Backlight Dimming ControlB2610 0033
I/P Dimmer Switch Ground1
1. Dimmer Switch Malfunction 2. Interior Backlighting Malfunction - Incandescent 3. Interior Backlighting Malfunction - LED

When the ignition switch is turned to the RUN position, the radio VF display turns ON at maximum brightness. When the park lamps are ON, all incandescent and LED back lighting turn ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time all VF displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the body control module (BCM). When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. When the I/P dimmer switch is moved from MIN to MAX, all VF displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 driver door switch while commanding the Driver Door Switch Integrated Sw. Backlighting Test ON and OFF with a scan tool. The switch backlighting should turn ON and OFF when changing between the commanded states. If the backlighting does not turn ON and OFF, replace the driver door lock and side window switch.
  2. Observe the passenger door switch while commanding the Passenger Door Switch Integrated Sw. Backlighting Test ON and OFF with a scan tool. The switch backlighting should turn ON and OFF when changing between the commanded states. If the backlighting does not turn ON and OFF, replace the passenger door lock and side window switch.
  3. Observe the scan tool Dimming Control Signal parameter while operating the dimmer switch from high to low. The reading should change from a high percent to a low percent as the switch is rotated. If the reading does not change between the selected states, refer to Dimmer Switch Malfunction below.
  4. Observe the function of the backlighting components while commanding the LED Dimming or Incandescent Dimming ON and OFF with a scan tool. The backlighting components should turn ON and OFF while changing between the commanded states. If the backlighting components do not turn ON and OFF, refer to Interior Backlighting Malfunction below.

Dimmer Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Ignition OFF, verify that a test lamp illuminates between the ground circuit terminal 8 and B+. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.1 V. If greater than the specified range, test the signal circuit terminal 13 for a short to voltage. If the circuit tests normal, replace the BCM.
  4. Ignition ON, test for B+ between the I/P dimming voltage reference circuit terminal 15 and ground. If less than the specified value, test the voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal 13 and the voltage reference circuit terminal 15. Verify the scan tool BCM Dimming Control Signal parameter is greater than 2.6 V. If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, replace the headlamp and panel dimmer switch.

Interior Backlighting Malfunction

  1. Ignition OFF, disconnect the harness connector at any component with inoperative backlighting.
  2. Ignition OFF, scan tool disconnected, interior lamps OFF, doors CLOSED, test for less than 5 ohms between the ground circuit 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 and ground.
  4. Command the LED Dimming or Incandescent Dimming 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the component with inoperative backlighting.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Door Lock and Side Window Switch Replacement - Driver Side»(/gmc/sierra-2500/2012-2012/remont/door-locks-anti-theft-systems/#power-door-lock-system-and-release-systems)
  2. «Door Lock and Side Window Switch Replacement - Passenger Side»(/gmc/sierra-2500/2012-2012/remont/door-locks-anti-theft-systems/#power-door-lock-system-and-release-systems)
  3. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  4. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM, IPC, radio, and HVAC control module replacement, programming, and setup.
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
PARK LAMP Relay Control11B2585 00
Park Lamp Switch ON Signal222
License Lamp Supply Voltage111
Park Lamp Voltage Supply111
License Lamp Ground1
Park Lamps - LF Ground1
Park Lamps - RF Ground1
Tail/Stop and Turn Signal Lamps - LR Ground1
Tail/Stop and Turn Signal Lamps - RR Ground1
Turn Signal/Multifunction Switch Ground2
1. Park, License, and/or Tail Lamps Malfunction 2. Park Lamp Switch Malfunction

B+ is applied at all times to both the coil and switch sides of the PARK LAMP Relay located in the underhood fuse block. The turn signal/multifunction switch is supplied with ground at all times. When the headlamp switch is placed in either the HEAD or PARK position, ground is applied to the park lamp signal circuit to the body control module (BCM). The BCM responds by applying ground to the park lamp relay control circuit. This energizes the park lamp relay coil causing the relay switch contacts to close allowing B+ to flow through the LT PRK, RT PRK, and TRLR PRK fuses, to all of the park, tail, license, and marker lamps.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 scan tool Parklamp Switch parameter while cycling the headlamp switch between the OFF and Park positions. The parameter should toggle between Active and Inactive. If the readings do not change between the commanded states, refer to Park Lamp Switch Malfunction below.
  2. Command the Parking Lamps ON and OFF with a scan tool. The park lamps should turn ON and OFF when changing between the commanded states. If the park lamps do not turn ON and OFF when commanded, refer to Park Lamps Malfunction below.

Park Lamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
  2. Test for less than 1.0 ohms between the ground circuit terminal 8 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Parklamp Switch parameter is Inactive. If not the specified value, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the BCM.
  4. Install a 3 A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Parklamp Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or open/high resistance. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Park Lamps Malfunction

  1. Ignition OFF, disconnect the park lamp 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 85 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. 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 an open/high resistance.
  5. Disconnect the harness connector at the appropriate park lamp.
  6. Test for less than 5 ohms between the park lamp ground circuit terminal listed below and ground: Park/Turn Signal Lamp - Terminal G Tail/Stop and Turn Signal Lamp - Terminal GRD License Lamp - Terminal B Rear Fender Clearance Lamp - Terminal B Side Marker Lamp - Terminal A Roof Clearance Lamp - Terminal A Tailgate Marker Lamp - Terminal B If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  7. Connect the harness connector at the park lamp.
  8. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the park lamp is activated. If the park lamp does not activate and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the park lamp. If the park lamp does not activate and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the park lamp.
  9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  10. Command the Parking 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 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 BCM.
  11. If all circuits test normal, test or replace the park lamp relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Parking and Turn Signal Lamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Parking and Turn Signal Lamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Rear License Plate Lamp Replacement (Silverado GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Rear License Plate Lamp Replacement (VF7)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Tail Lamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  4. «Headlamp Switch Replacement (without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Switch Replacement (with RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  5. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup.
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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 Position Sensor 5 V ReferenceC0277 06, C0890 03C0277 061
Brake Applied SignalC0297 00 and P0571 0033
Brake Position Sensor SignalC0277 06C0277 06C0277 07C0277 09
Center High Mounted Stop Lamp (CHMSL) Relay ControlB3884 0022
Left Rear Stop/Turn Lamp Control111
Right Rear Stop/Turn Lamp Control111
Brake Position Sensor Low ReferenceC0277 071
Center High Mounted Stop Lamp (CHMSL) Ground22
Left Rear Stop/Turn Lamp Ground11
Right Rear Stop/Turn Lamp Ground11
1. Stop Lamps Malfunction 2. Center High Mounted Stop Lamp (CHMSL) Malfunction 3. 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, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) control circuit.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 scan tool Brake Applied Output Signal parameter while pressing and releasing the brake pedal. The parameter should change between ON and OFF as the brake pedal is applied and released. If the parameter does not change between the selected states, refer to the Brake Pedal Position Sensor Malfunction below.
  2. Observe the left and right stop lamps while applying and releasing the brake pedal. The stop lamps should turn ON and OFF as the brake pedal is applied and released. If the left or right stop lamps do not change between the selected states, refer to the Stop Lamp Malfunction below.
  3. Observe the center high mount stop lamp while pressing and releasing the brake pedal. The center high mount stop lamp should turn ON and OFF as the brake pedal is applied and released. If the center high mount stop lamp does not change between the selected states, refer to Center High Mount Stop Lamp Malfunction below.

Brake Pedal Position Sensor Malfunction

  1. Ignition OFF, disconnect the harness connector at the brake pedal position sensor.
  2. Ignition ON, verify that a test lamp does not illuminate between the low reference circuit terminal 2 and ground. If the test lamp illuminates, test the low reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  3. Ignition ON, test for 4.8 V and 5.2 V between the 5 V reference circuit terminal 1 and ground. If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  4. If all circuits test normal, replace the brake pedal position sensor.

Stop Lamp Malfunction

  1. Ignition OFF, disconnect the X4 harness connector at the BCM.
  2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminals listed below and ground: Terminal 1 Terminal 2 Terminal 4 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 X4 harness connector at the BCM.
  4. Disconnect the harness connector at the appropriate stop lamp.
  5. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal GRD and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  6. Connect a test lamp between the stop lamp control circuit terminal MJR and ground.
  7. Ignition ON, command the stop lamps ON and OFF by applying and releasing the brake pedal. 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 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 BCM.
  8. If all circuits test normal, replace the inoperative stop lamp.

Center High Mount Stop Lamp Malfunction

  1. Ignition OFF, disconnect the X5 harness connector at the fuse block - underhood.
  2. Connect a test lamp between the control circuit terminal K6 and B+.
  3. Ignition ON, command the stop lamps ON and OFF by applying and releasing the brake pedal. 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 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 BCM.
  4. Ignition OFF, connect the X5 harness connector at the fuse block - underhood. Disconnect the harness connector at the center high mount stop lamp.
  5. Disconnect the harness connector at the center high mount stop lamp.
  6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal B and ground If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect a test lamp between the control circuit terminal A and ground.
  8. Ignition ON, command the stop lamps ON and OFF by applying and releasing the brake pedal. 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 fuse block - underhood. 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 fuse block - underhood.
  9. If all circuits test normal, replace the center high mount stop lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «High Mount Stop Lamp Replacement (Extended and Crew Cab)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «High Mount Stop Lamp Replacement (Regular Cab)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Tail Lamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Tail Lamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (HD)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  4. «Brake Pedal Position Sensor Replacement (Without JF4)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-replacement-without) , «Brake Pedal Position Sensor Replacement (With JF4)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-replacement-with)
  5. «Brake Pedal Position Sensor Calibration»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-calibration)
  6. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM replacement, programming, and setup.
  1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/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
CTSY Fuse B+11
RT STOP TRN Fuse B+11
LT STOP TRN Fuse B+11
Hazard Switch Signal222
Left Turn Signal Switch Signal333
Right Turn Signal Switch Signal333
Hazard Switch Ground2
Stop/Tail/Turn Signal Lamp - LR Ground1
Stop/Tail/Turn Signal Lamp - RR Ground1
Turn Signal/Multifunction Switch Ground3
Turn Signal Lamp - LF Ground1
Turn Signal Lamp - RF Ground11
1. Turn Signal Lamps and/or Indicators Malfunction 2. Hazard Lamps Malfunction 3. Turn Signal Switch 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 position. 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 then applies a pulsating voltage to the front and rear turn signal lamps through their respective control circuits.

An open CTSY fuse located in the I/P fuse block will affect the operation of the right front turn signal only.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
  4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 scan tool Right Turn Signal Switch and Left Turn Signal Switch parameters while cycling the turn signal switch between the right and left positions. The parameters should change between Active and Inactive. If the parameters do not change between the selected states, refer to Turn Signal Switch Malfunction below.
  2. Ignition ON, observe the right and left turn signal lamps while cycling the turn signal switch between the right and left positions. Verify the turn signal lamps turn ON and OFF. If the turn signal lamps do not cycle between the selected states, refer to Turn Signal Lamps Malfunction below.
  3. Command the Lamp Test ON and OFF with a scan tool. The left and right turn signal indicators should turn ON and OFF when changing between the commanded states. If the left and right turn signal indicators illuminate during the test, replace the BCM. If the left and right turn signal indicators do not illuminate during the test or remain illuminated at all times, replace the instrument cluster.

Turn Signal Switch Malfunction

  1. Ignition OFF, disconnect the X1 harness connector at the turn signal/multifunction switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal F. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Left Turn Signal Switch parameter is Inactive. If not the specified value, test the signal circuit terminal E for a short to ground. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool Right Turn Signal Switch parameter is Inactive. If not the specified value, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the BCM.
  5. Install a 3 A fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool Left Turn Signal Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  6. Install a 3 A fused jumper wire between the signal circuit terminal D and ground. Verify the scan tool Right Turn Signal Switch parameter is Active. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the turn signal/multifunction switch.

Turn Signal Lamps Malfunction

  1. Ignition OFF, disconnect the X4 harness connector at the BCM.
  2. Verify that a test lamp illuminates between the B+ circuit terminal 1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. 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.
  4. 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.
  5. Ignition OFF, connect the X4 harness connector at the BCM.
  6. Ignition OFF, disconnect the harness connector at the appropriate turn signal lamp.
  7. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal listed below and ground: Park/Turn Signal Lamp - Terminal G Tail/Stop and Turn Signal Lamp - Terminal GRD If greater than the specified range, test the ground circuit for an open/high resistance.
  8. Connect a test lamp between the control circuit terminal listed below and ground: Park/Turn Signal Lamp - Terminal MIN Tail/Stop and Turn Signal Lamp - Terminal MJR
  9. Command the appropriate turn signal 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 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 BCM.
  10. If all circuits test normal, replace the turn signal lamp.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Parking and Turn Signal Lamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Parking and Turn Signal Lamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  2. «Tail Lamp Bulb Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Bulb Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  3. «Turn Signal Multifunction Switch Replacement»(/gmc/sierra-2500/2012-2012/remont/steering-column-switches/#steering-wheel-and-steering-column)
  4. «Headlamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Headlamp Replacement (HD Chevrolet Diesel)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__headlamp-replacement-hd-chevrolet-diesel) , «Headlamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__headlamp-replacement-gmc)
  5. «Tail Lamp Replacement (Chevrolet)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (HD)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system) , «Tail Lamp Replacement (GMC)»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
  6. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or IPC replacement, setup, and programming

Brake Pedal Position Sensor Calibration

Note. Brake system does not use a brake switch, stoplight switch or brakelight switch. System uses a Brake Pedal Position Sensor to control these functions.

Calibration Criteria

IMPORTANTDo not apply the brake pedal during the brake pedal position sensor calibration procedure. Any movement of the brake pedal during this procedure will cause the calibration procedure to fail. If this occurs, the brake pedal position sensor (BPPS) calibration must be repeated.

Brake pedal position sensor calibration must be performed after the brake pedal position sensor or body control module (BCM) have been serviced. The calibration procedure will set the brake pedal position sensor home value. This value is used by the BCM to determine the action of the driver applying the brake system and to provide this information to the vehicle subsystems via the GMLAN communication bus.

Calibration Procedure

  1. Apply the parking brake.
  2. Place the transmission in the PARK position.
  3. Install a scan tool.
  4. Clear all BCM DTCs before proceeding.
  5. Navigate to the Vehicle Control Systems menu.
  6. Select Module Setup menu item.
  7. Select BCM menu item.
  8. Select the BPP Sensor Calibration procedure and follow the directions displayed on the screen.

Brake Pedal Position Sensor Replacement (Without JF4 - Pedals - Adjustable, Power)

Note. Brake system does not use a brake switch, stoplight switch or brakelight switch. System uses a Brake Pedal Position Sensor to control these functions.

Removal Procedure

  1. Place the ignition switch in the OFF position.
  2. Disconnect the brake pedal position sensor electrical connector.
  3. Remove the brake pedal position sensor bolt (1).
  4. Remove the brake pedal position sensor (1).

Installation Procedure

  1. Install the brake pedal position sensor (1).
  2. Install the brake pedal position sensor bolt (1).
  3. Connect the brake pedal position sensor electrical connector.
  4. Calibrate the brake pedal position sensor. Refer to «Brake Pedal Position Sensor Calibration»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-calibration) .

Brake Pedal Position Sensor Replacement (With JF4 - Pedals - Adjustable, Power)

Note. Brake system does not use a brake switch, stoplight switch or brakelight switch. System uses a Brake Pedal Position Sensor to control these functions.

  1. Place the ignition switch in the OFF position.
  2. Disconnect the brake pedal position sensor electrical connector.
  3. Remove the brake pedal position sensor bolt (1).
  4. Remove the brake pedal position sensor (1).
  1. Install the brake pedal position sensor (1).
  2. Install the brake pedal position sensor bolt (1).
  3. Connect the brake pedal position sensor electrical connector.
  4. Calibrate the brake pedal position sensor. Refer to «Brake Pedal Position Sensor Calibration»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system__brake-pedal-position-sensor-calibration) .

Scheme 22

Scheme 22: Headlamp Switch Replacement (with RPO SLT)
Scheme 22: Headlamp Switch Replacement (with RPO SLT)
CalloutComponent Name
1Headlamp Switch Trim Plate Assembly Refer to Headlamp Switch Bezel Replacement (SLT) .
2Headlamp and I/P Lamp Dimmer and Dome Lamp Switch Assembly

Headlamp Switch Replacement (with RPO SLT)

Scheme 23

Scheme 23: Headlamp Switch Replacement (without RPO SLT)
Scheme 23: Headlamp Switch Replacement (without RPO SLT)
CalloutComponent Name
1Instrument Panel Trim Plate Assembly Refer to Instrument Panel Trim Plate Replacement (Without RPO SLT)
2Headlamp and I/P Lamp Dimmer and Dome Lamp Switch Assembly

Headlamp Switch Replacement (without RPO SLT)

Fog Lamp Switch Replacement (with RPO SLT)

CalloutComponent Name
1Headlamp Switch Trim Plate Assembly Refer to Headlamp Switch Bezel Replacement (SLT) .
2Headlamp and I/P Lamp Dimmer and Dome Lamp Switch Assembly TIP: Fog lamp switch is an integral part of the headlamp switch and the unit must therefore be replaced in whole.

Fog Lamp Switch Replacement (with RPO SLT)

Fog Lamp Switch Replacement (without RPO SLT)

CalloutComponent Name
1Instrument Panel Trim Plate Assembly Refer to Instrument Panel Trim Plate Replacement (Without RPO SLT) .
2Headlamp and I/P Lamp Dimmer and Dome Lamp Switch Assembly TIP: Fog lamp switch is an integral part of the headlamp switch and the unit must therefore be replaced in whole.

Fog Lamp Switch Replacement (without RPO SLT)

Scheme 24

Scheme 24: Ambient Light Sensor Replacement
Scheme 24: Ambient Light Sensor Replacement
CalloutComponent Name
1Instrument Panel Trim Panel Refer to Instrument Panel Upper Trim Panel with Windshield Defroster Nozzle Grille Replacement (with RPO SLT) , Instrument Panel Upper Trim Panel with Windshield Defroster Nozzle Grille Replacement (without RPO SLT) .
2Headlamp Auto Control Ambient Light Sensor Assembly Twist and pull down to remove. Disconnect electrical connector.

Ambient Light Sensor Replacement

Scheme 25

Scheme 25: Outside Rearview Mirror Courtesy Lamp Replacement
Scheme 25: Outside Rearview Mirror Courtesy Lamp Replacement
CalloutComponent Name
Fastener Tightening Specifications: Refer to Fastener Tightening Specifications .
1Exterior Courtesy Lamp Assembly Use a flat-bladed tool to pry off assembly starting at end closest to door. Tilt assembly end and pull down to release. Disconnect electrical connector.
2Exterior Courtesy Lamp Socket TIP: Twist and pull to release.
3Exterior Courtesy Lamp Bulb

Outside Rearview Mirror Courtesy Lamp Replacement

Scheme 26

Scheme 26: Dome Lamp Replacement
Scheme 26: Dome Lamp Replacement
CalloutComponent Name
1Dome Lamp Lens TIP: Using a flat-bladed tool pry down on right side of lens to avoid damaging tab.
2Dome Lamp Housing TIP: Disconnect electrical connector.

Dome Lamp Replacement

Scheme 27

Scheme 27: Headlamp Replacement (Chevrolet)
Scheme 27: Headlamp Replacement (Chevrolet)
CalloutComponent Name
Preliminary Procedure Remove the upper radiator grille. Refer to Radiator Grille Replacement (GMC) , Radiator Grille Replacement (Chevrolet) , Radiator Grille Replacement (Chevrolet HD) , Radiator Grille Replacement (GMC HD) . Behind the headlamp at the top of the front bumper access the lower inside hidden headlamp bolt. Loosen the bolt only, do not remove, the lower outside hidden headlamp bolt.
1Headlamp Screws (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 6 N.m (53 lb in)
2Headlamp Screw (Hidden) Tighten 6 N.m (53 lb in)
3Headlamp Housing Support Procedure Apply masking tape to the front bumper end caps to protect the painted surface. For the right side lamp assembly only, disengage the upper retainer for the radiator air baffle. Release the headlamp from the support tab, rotate the lamp assembly towards the center of the vehicle. Disengage the headlamp electrical connector from the forward lamp harness.
CAUTION
Refer to Fastener Caution .

Headlamp Replacement (Chevrolet)

Headlamp Replacement (GMC)

CalloutComponent Name
Preliminary Procedures Remove the radiator grille. Refer to Radiator Grille Replacement (GMC) , Radiator Grille Replacement (Chevrolet) , Radiator Grille Replacement (Chevrolet HD) , Radiator Grille Replacement (GMC HD) . Loosen only, do not remove, the lower outside hidden headlamp bolt (2). Depress the housing support tab with a flat-bladed tool downward in order to release the headlamp assembly from the support. Pull the lamp assembly slightly forward to access the electrical connection. Disconnect the forward lamp harness main electrical connector from the headlamp harness.
1Headlamp Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 6 N.m (53 lb in)
2Headlamp Screw (Hidden) Tighten 6 N.m (53 lb in)
3Headlamp Housing Support
CAUTION
Refer to Fastener Caution .

Headlamp Replacement (GMC)

Headlamp Replacement (HD Chevrolet Diesel)

CalloutComponent Name
Preliminary Procedure Lower the front bumper impact bar. Refer to Front Bumper Impact Bar Replacement (GMC) , Front Bumper Impact Bar Replacement (Chevrolet) . Loosen only, do not remove, the lower outside hidden headlamp bolt (2). Depress the housing support tab with a flat-bladed tool downward in order to release the headlamp assembly from the support. Pull the lamp assembly slightly forward to access the electrical connection. Disconnect the forward lamp harness main electrical connector from the headlamp harness.
1Headlamp Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 6 N.m (53 lb in)
2Headlamp Screw (Hidden) Tighten 6 N.m (53 lb in)
3Headlamp Housing Support
CAUTION
Refer to Fastener Caution .

Headlamp Replacement (HD Chevrolet Diesel)

Scheme 28

Scheme 28: Headlamp Bulb Replacement (Chevrolet)
Scheme 28: Headlamp Bulb Replacement (Chevrolet)
CalloutComponent Name
Preliminary Procedures Open and support the hood assembly. If replacing the headlamp bulbs on the passenger side, remove the air cleaner box assembly. Refer to Air Cleaner Assembly Replacement . If replacing the headlamp bulbs on the driver side, remove the auxiliary battery, (if equipped). Refer to Auxiliary Battery Replacement . If no auxiliary battery is used, just reach in and access the bulb sockets from inside the engine compartment, disconnect the headlamp bulb electrical connector. Rotate the bulb socket counter-clockwise and remove from the headlamp composite.
1Headlamp Bulb (Hi) WARNING: Refer to Halogen Bulb Warning . TIP: Disconnect the headlamp bulb electrical connector from the headlamp bulb socket assembly.
2Headlamp Bulb (Lo) TIP: Disconnect the headlamp bulb electrical connector from the headlamp bulb socket assembly.
WARNING
Refer to Halogen Bulb Warning .

Headlamp Bulb Replacement (Chevrolet)

Scheme 29

Scheme 29: Headlamp Bulb Replacement (GMC)
Scheme 29: Headlamp Bulb Replacement (GMC)
CalloutComponent Name
Preliminary Procedures Open and support the hood assembly. If replacing the headlamp bulbs on the passenger side, remove the air cleaner box assembly. Refer to Air Cleaner Assembly Replacement . If replacing the headlamp bulbs on the driver side, remove the auxiliary battery, (if equipped). Refer to Auxiliary Battery Replacement . If no auxiliary battery is used, just reach in and access the bulb sockets from inside the engine compartment, disconnect the headlamp bulb electrical connector. Rotate the bulb socket counter-clockwise and remove from the headlamp composite.
1Headlamp Bulb (Hi) WARNING: Refer to Halogen Bulb Warning . TIP: Disconnect the headlamp bulb electrical connector from the headlamp bulb socket assembly.
2Headlamp Bulb (Lo) TIP: Disconnect the headlamp bulb electrical connector from the headlamp bulb socket assembly.
WARNING
Refer to Halogen Bulb Warning .

Headlamp Bulb Replacement (GMC)

Headlamp Aiming (Chevrolet/GMC)

Headlamp aiming is done with the low beam lamps. The high beam lamps will be correctly aimed if the low beam lamps are aimed properly.

Screen Method for Headlamp Aiming (Visual Aim)

The screen method requires an area set up specifically for headlamp aim.

The area should consist of a level surface large enough to allow for a vehicle and an additional 7.62 m (25 ft) as measured from the face of the headlamps to the aiming screen.

The screen should be a wall or other flat surface at least 1.52 m (5 ft) high by 3.66 m (12 ft) wide with a matte white surface well shaded from extraneous light, and 90 degrees to the floor. The screen should be provided with a permanent vertical reference line 0.61 m (2 ft) from the left edge of the screen, 2 laterally adjustable vertical tapes, and one vertically adjustable horizontal tape.

After the aiming screen has been set up and located, paint or tape a reference line on the floor 15.24 m (50 ft) from the vertical reference line on the screen. This line should be perpendicular to the aiming screen and a mark placed at 7.62 m (25 ft) from the screen.

Headlamp Aiming Procedure

  1. Align the left tires of the vehicle with the reference line extending from the screen with the headlamps aligned with the reference line.
  2. Remove any snow, ice or mud from the vehicle.
  3. The vehicle should be fully assembled and all other work stopped while the headlamp aiming is being done.
  4. The vehicle should contain cargo or be loaded to represent normal vehicle use.
  5. Tires should be properly inflated.
  6. Rock the vehicle to stabilize the suspension.
  7. Measure from the floor to the center of the lamp bulb on the vehicle. Some lamps have an aim dot marked on the lens.
  8. At the screen, measure from the floor and place the horizontal tape at the measured distance.
  9. Measure from the reference line on the floor to the left headlamp bulb centerline (1).
  10. At the screen, measure from the reference line and place the vertical tape at the measured distance (2).
  11. Measure from the reference line on the floor to the right headlamp bulb centerline.
  12. At the screen, measure from the reference line and place the vertical tape at the measured distance.
  13. Turn the headlamps ON.
  14. Block the light from projecting onto the screen from the passenger side headlamp. This will allow the cutoff in the beam pattern from the drivers side to be more pronounced for easier aim verification.
  15. On this vehicle you will be verifying the aim of the vertical cutoff on the right side of the lamp vertical bulb centerline as it is projected onto the aim board.
  16. If the location of the cutoff projected onto the board differs from (Scheme 4) then an adjustment to the beam pattern location is necessary.
  17. Adjust the vertical headlamp adjustment screw until the Right Gradient Line (Cutoff Line) is set at the Horizontal Axis within +/- 2.0 inches (2) measured at 7.62 m (25 ft).
  18. Verify proper aim location.
  19. Repeat the aiming procedure for the passengers side headlamp while blocking the light from projecting onto the screen from the drivers side headlamp.

Scheme 30

Scheme 30: Front Fog Lamp Replacement (Chevrolet)
Scheme 30: Front Fog Lamp Replacement (Chevrolet)
CalloutComponent Name
Preliminary Procedures Remove either the LF or RF wheelhouse liners. Refer to Front Wheelhouse Liner Replacement - Left Side (GMC) , Front Wheelhouse Liner Replacement - Left Side (Chevrolet) , for the LF or Front Wheelhouse Liner Replacement - Right Side (GMC) , Front Wheelhouse Liner Replacement - Right Side (Chevrolet) for the RF wheelhouse liner. Disconnect the electrical connector. From inside the front air deflector, using a six point 10 mm socket or the open end of a 3/8" extension, compress the retainers and push outward on the two upper mounting studs for the fog lamp. Using the same tools, compress the lower retainer and press outward on the low Remove the fog lamp assembly from the lower air deflector.
1Fog Lamp Retainers (Qty: 3) Procedure Install the retainers back onto the fog lamp upper mounting studs. Install the retainer onto the fog lamp adjusting screw. Firmly push the lamp assembly back into the lower air deflector until all three retainers are engaged to the air deflector. Aim the fog lamps after the fog lamp has been replaced. Refer to Fog Lamp Aiming .
2Fog Lamp Assembly WARNING: Refer to Halogen Bulb Warning . Transfer the bulb assembly as needed.
WARNING
Refer to Halogen Bulb Warning .

Front Fog Lamp Replacement (Chevrolet)

Scheme 31

Scheme 31: Front Fog Lamp Replacement (GMC)
Scheme 31: Front Fog Lamp Replacement (GMC)
CalloutComponent Name
Preliminary Procedures Remove either the LF or RF wheelhouse liners. Refer to Front Wheelhouse Liner Replacement - Left Side (GMC) , Front Wheelhouse Liner Replacement - Left Side (Chevrolet) , for the LF or Front Wheelhouse Liner Replacement - Right Side (GMC) , Front Wheelhouse Liner Replacement - Right Side (Chevrolet) for the RF wheelhouse liner. Disconnect the electrical connector. From inside the front air deflector, using a six point 10 mm socket or the open end of a 3/8" extension, compress the retainers and push outward on the two upper mounting studs on the fog lamp. Using the same tools, compress the lower retainer and push outward on the adjustment screw for the fog lamp. Remove the fog lamp assembly.
1Fog Lamp Assembly WARNING: Refer to Halogen Bulb Warning . TIP: Transfer the bulb assembly as needed.
2Fog Lamp Retainers (Qty: 3) Procedure Install the retainers back onto the fog lamp upper mounting studs. Install the retainer onto the fog lamp adjusting screw. Firmly push the lamp assembly back into the front air deflector until all three retainers are engaged to the air deflector. Aim the fog lamps after the fog lamp has been replaced. Refer to Fog Lamp Aiming .
WARNING
Refer to Halogen Bulb Warning .

Front Fog Lamp Replacement (GMC)

Scheme 32

Scheme 32: Front Fog Lamp Bulb Replacement (Chevrolet)
Scheme 32: Front Fog Lamp Bulb Replacement (Chevrolet)
CalloutComponent Name
Preliminary Procedures Reach under the front air deflector in order to access the fog lamp bulb socket. Disconnect the electrical connector.
1Fog Lamp Bulb WARNING: Refer to Halogen Bulb Warning . TIP: Squeeze the tabs and rotate in order to release the bulb socket from the fog lamp assembly.
WARNING
Refer to Halogen Bulb Warning .

Front Fog Lamp Bulb Replacement (Chevrolet)

Scheme 33

Scheme 33: Front Fog Lamp Bulb Replacement (GMC)
Scheme 33: Front Fog Lamp Bulb Replacement (GMC)
CalloutComponent Name
Preliminary Procedures Reach under the front air deflector in order to access the bulb socket. Disconnect the electrical connector.
1Fog Lamp Bulb WARNING: Refer to Halogen Bulb Warning . TIP: Squeeze the tabs and rotate the bulb socket in order to release the bulb socket from the fog lamp assembly.
WARNING
Refer to Halogen Bulb Warning .

Front Fog Lamp Bulb Replacement (GMC)

Scheme 34

Scheme 34: Front Fog Lamp Cover Replacement (GMC HD)
Scheme 34: Front Fog Lamp Cover Replacement (GMC HD)
CalloutComponent Name
Preliminary Procedure Reach under the front lower air deflector in order to access and release the front fog lamp opening cover clips from the air deflector.
1Front Fog Lamp Opening Cover

Front Fog Lamp Cover Replacement (GMC HD)

Fog Lamp Aiming

The front fog lamps must be aimed for proper illumination of the road. The front fog lamp aim should be checked when a new front fog lamp assembly is installed, or if service or repairs in the front end area may have disturbed the front fog lamp mounting.

Preparation Procedure

IMPORTANTHorizontal aim is not adjustable on this vehicle. Vertical aim is adjusted by an adjusting screw located on the bottom rear of the fog lamp. Prior to aiming the fog lamps, perform the following steps
  1. Completely assemble all of the components on the vehicle.
  2. Park the vehicle on a level surface.
  3. Stop all unnecessary operations or work on the vehicle that affect the vehicle trim.
  4. Close the doors and ensure that the vehicle has no load other than the driver.
  5. Stabilize the suspension by rocking the vehicle sideways.
  6. Ensure that the fuel level is 1/2 full.
  7. Ensure that the tires are inflated to the proper pressure.
  8. Ensure that the driver or a similar weight, approximately 75 kg (165 lb), is in the vehicle driver seat.

Aiming Procedure

  1. Park the vehicle on a level surface 7.6 m (25 ft) (3) away from a wall or other flat surface.
  2. Measure the distance from the floor to the center of the fog lamp (5).
  3. Using this measurement, mark the horizontal centerline of the fog lamp (1) on the flat surface directly in front of the vehicle.
  4. Remove the front portion of the front wheel liner in order to access the adjusting screw.
  5. Turn ON the fog lamps.
  6. Reach inside of the front portion of the fender liner in order to access the fog lamp vertical adjustment screw on the bottom of the fog lamp.
  7. Adjust the fog lamp so that the top edge of the fog lamp beam pattern is 100 mm (4 in) below the horizontal centerline (2).
  8. Turn OFF the fog lamps.
  9. Secure the forward edge of the front fender liner.

Scheme 35

Scheme 35: Front Side Marker Lamp Bulb Replacement (GMC)
Scheme 35: Front Side Marker Lamp Bulb Replacement (GMC)
CalloutComponent Name
Preliminary Procedure Remove either the LF or RF headlamp assembly. Refer to Headlamp Replacement (Chevrolet) , Headlamp Replacement (HD Chevrolet Diesel) , Headlamp Replacement (GMC) .
1Lamp Harness Socket TIP: Rotate the marker lamp socket a quarter turn counterclockwise and remove the lamp socket from the headlamp assembly.
2Front Side Marker Lamp Bulb TIP: Pull the front side marker lamp bulb straight from the lamp socket.

Front Side Marker Lamp Bulb Replacement (GMC)

Scheme 36

Scheme 36: Roof Clearance Center Lamp Replacement (U01)
Scheme 36: Roof Clearance Center Lamp Replacement (U01)
CalloutComponent Name
1Screw (Qty: 3) CAUTION: Refer to Fastener Caution . Tighten 2 N.m (18 lb in)
2Roof Clearance Center Lamp TIP: Lift the lamp cover lens and replace the bulb as needed.
CAUTION
Refer to Fastener Caution .

Roof Clearance Center Lamp Replacement (U01)

Scheme 37

Scheme 37: Roof Clearance Outer Lamp Replacement (U01)
Scheme 37: Roof Clearance Outer Lamp Replacement (U01)
CalloutComponent Name
1Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 2 N.m (18 lb in)
2Roof Clearance Outer Lamp TIP: Lift the lamp cover lens and replace the bulb as needed.
CAUTION
Refer to Fastener Caution .

Roof Clearance Outer Lamp Replacement (U01)

Scheme 38

Scheme 38: Parking and Turn Signal Lamp Bulb Replacement (GMC)
Scheme 38: Parking and Turn Signal Lamp Bulb Replacement (GMC)
CalloutComponent Name
Preliminary Procedure Remove either the LF or RF headlamp assembly. Refer to Headlamp Replacement (Chevrolet) , Headlamp Replacement (HD Chevrolet Diesel) , Headlamp Replacement (GMC) .
1Directional Lamp Bulb Socket TIP: Rotate the marker lamp socket a quarter turn counterclockwise and remove the lamp socket from the headlamp assembly.
2Directional / DRL Bulb TIP: Pull the marker lamp bulbs straight from the lamp bulb socket.

Parking and Turn Signal Lamp Bulb Replacement (GMC)

Scheme 39

Scheme 39: Parking and Turn Signal Lamp Bulb Replacement (Chevrolet)
Scheme 39: Parking and Turn Signal Lamp Bulb Replacement (Chevrolet)
CalloutComponent Name
Preliminary Procedure Remove either the LF or RF headlamp assembly in order to access the headlamp bulbs. Refer to Headlamp Replacement (Chevrolet) , Headlamp Replacement (HD Chevrolet Diesel) , Headlamp Replacement (GMC) .
1Directional Bulb Sockets (Qty: 2) WARNING: Refer to Halogen Bulb Warning . TIP: Rotate the bulb sockets a quarter turn counter-clockwise to access the bulbs.
2Directional Bulbs (Qty: 2) TIP: Pull the bulbs straight from the lamp sockets.
WARNING
Refer to Halogen Bulb Warning .

Parking and Turn Signal Lamp Bulb Replacement (Chevrolet)

Scheme 40

Scheme 40: Pickup Box Identification Lamp Replacement (Chevrolet HD)
Scheme 40: Pickup Box Identification Lamp Replacement (Chevrolet HD)
CalloutComponent Name
1Pick Up Box Identification Lamp Assembly TIP: Release the 3 integral clips securing the lamp assembly to the pick up box end panel.
2Pick Up Box Identification Lamp Electrical Connector

Pickup Box Identification Lamp Replacement (Chevrolet HD)

Scheme 41

Scheme 41: Pickup Box Identification Lamp Replacement (GMC HD)
Scheme 41: Pickup Box Identification Lamp Replacement (GMC HD)
CalloutComponent Name
1Pick Up Box Identification Lamp Assembly Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 2.5 N.m (22 lb in)
2Pick Up Box Identification Lamp Assembly
3Pick Up Box Identification Lamp Electrical Connector
4Rear Cross Sill Nut (Qty: 2)
CAUTION
Refer to Fastener Caution .

Pickup Box Identification Lamp Replacement (GMC HD)

Scheme 42

Scheme 42: Rear Fender Clearance Lamp Replacement
Scheme 42: Rear Fender Clearance Lamp Replacement
CalloutComponent Name
Preliminary Procedure Reach inside the rear fender and wheelhouse in order to disconnect the electrical connector for the rear fender lamp from the main chassis harness. Disengage the retainer securing the connector to the pick up box panel brace. From inside the wheelhouse push inward on the locking tab for the lamp assembly and push the lamp outward from the fender. Remove the lamp and electrical harness.
1Rear Fender Clearance Lamps TIP: The amber lens is installed to the front of the rear fender and the red lens is installed at the rear of the rear fender.

Rear Fender Clearance Lamp Replacement

Scheme 43

Scheme 43: High Mount Stop Lamp Replacement (Extended and Crew Cab)
Scheme 43: High Mount Stop Lamp Replacement (Extended and Crew Cab)
CalloutComponent Name
1High Mounted Stop and Cargo Lamp Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 2.5 N.m (22 lb in)
2High Mounted Stop and Cargo Lamp Procedure Pull the lamp rearward in order to access the electrical connector. Disconnect the electrical connector.
CAUTION
Refer to Fastener Caution .

High Mount Stop Lamp Replacement (Extended and Crew Cab)

Scheme 44

Scheme 44: High Mount Stop Lamp Replacement (Regular Cab)
Scheme 44: High Mount Stop Lamp Replacement (Regular Cab)
CalloutComponent Name
1High Mounted Stop and Cargo Lamp Opening Cover Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 2.5 N.m (22 lb in)
2High Mounted Stop and Cargo Lamp Opening Cover TIP: Pull the lamp rearward in order to access the electrical connector.
CAUTION
Refer to Fastener Caution .

High Mount Stop Lamp Replacement (Regular Cab)

Scheme 45

Scheme 45: High Mount Stop Lamp Bulb Replacement (GMC Denali)
Scheme 45: High Mount Stop Lamp Bulb Replacement (GMC Denali)
CalloutComponent Name
Preliminary Procedure Remove the high mounted stop lamp cover assembly. Refer to High Mount Stop Lamp Replacement (Extended and Crew Cab) , High Mount Stop Lamp Replacement (Regular Cab) .
1High Mounted Stop and Cargo Lamp Opening Cover Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 2.5 N.m (22 lb in)
2High Mounted Stop and Cargo Lamp Opening Cover
3Cargo Lamp Bulb (Qty: 2) TIP: Rotate the bulb sockets a quarter turn counter-clockwise to unlock in order to remove the bulbs from the bulb sockets.
4Brake Lamp Bulb (Qty: 2) TIP: Rotate the bulb sockets a quarter turn counter-clockwise to unlock in order to remove the bulbs from the bulb sockets.
CAUTION
Refer to Fastener Caution .

High Mount Stop Lamp Bulb Replacement (GMC Denali)

Scheme 46

Scheme 46: Backup Lamp Bulb Replacement (Chevrolet)
Scheme 46: Backup Lamp Bulb Replacement (Chevrolet)
CalloutComponent Name
Preliminary Procedure Remove either the LR or RR tail lamp assembly. Refer to Tail Lamp Replacement (Chevrolet) , Tail Lamp Replacement (HD) , Tail Lamp Replacement (GMC) .
1Back Up Lamp Bulb

Backup Lamp Bulb Replacement (Chevrolet)

Scheme 47

Scheme 47: Backup Lamp Bulb Replacement (GMC)
Scheme 47: Backup Lamp Bulb Replacement (GMC)
CalloutComponent Name
Preliminary Procedure Remove either the LR or RR tail lamp assembly. Refer to Tail Lamp Replacement (Chevrolet) , Tail Lamp Replacement (HD) , Tail Lamp Replacement (GMC) .
1Back Up Lamp Bulb

Backup Lamp Bulb Replacement (GMC)

  1. Ensure the headlamp switch is in the OFF position.
  2. Reach under the rear bumper and press on the lens end of the cover in order to release the locking tab.
  3. Remove the lens housing from the bumper assembly.
  4. Remove the bulb.
  1. Install the bulb.
  2. Install the rear edge of the lens housing into the rear bumper.
  3. Push on the lens side of the housing in order to snap the housing into the rear bumper assembly.
  4. Inspect the operation.

Scheme 48

Scheme 48: Rear License Plate Lamp Replacement (VF7)
Scheme 48: Rear License Plate Lamp Replacement (VF7)
CalloutComponent Name
1License Plate Lamp Electrical Connector TIP: Disconnect the electrical connector from the rear junction block.
2Rear License Plate Lamp Assembly

Rear License Plate Lamp Replacement (VF7)

Scheme 49

Scheme 49: Rear License Plate Lamp Bulb Replacement
Scheme 49: Rear License Plate Lamp Bulb Replacement
CalloutComponent Name
Procedure Reach under the rear bumper for the bulb socket. Turn the bulb socket counter-clockwise and pull the bulb socket out of the connector. Pull the old bulb from the socket, keeping the bulb straight as you pull it out. Install the new bulb.
1Bulb Socket
2Rear License Plate Lamp Bulb

Rear License Plate Lamp Bulb Replacement

Scheme 50

Scheme 50: Tail Lamp Replacement (Chevrolet)
Scheme 50: Tail Lamp Replacement (Chevrolet)
CalloutComponent Name
Preliminary Procedure Open the endgate in order to access the tail lamp assembly screws.
1Tail Lamp Assembly Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 2 N.m (18 lb in)
2Tail Lamp Wiring Harness Assembly Connector
3Tail Lamp Assembly TIP: Upon installation, push inward on the tail lamp in order to seat the 2 locating pins in the body panel.
CAUTION
Refer to Fastener Caution .

Tail Lamp Replacement (Chevrolet)

Scheme 51

Scheme 51: Tail Lamp Replacement (GMC)
Scheme 51: Tail Lamp Replacement (GMC)
CalloutComponent Name
Preliminary Procedures Open the endgate in order to access the tail lamp assembly screws. Disconnect the electrical harness to the tail lamp.
1Tail Lamp Assembly Screws (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 2 N.m (18 lb in)
2Tail Lamp Assembly TIP: Upon installation, push inward on the outer edge of the tail lamp in order to seat the 2 locating pins in the body panel.
CAUTION
Refer to Fastener Caution .

Tail Lamp Replacement (GMC)

Scheme 52

Scheme 52: Tail Lamp Replacement (HD)
Scheme 52: Tail Lamp Replacement (HD)
CalloutComponent Name
Preliminary Procedures Open the endgate in order to access the tail lamp assembly screws. Disconnect the electrical harness to the tail lamp.
1Tail Lamp Assembly Screw (Qty: 2) CAUTION: Refer to Fastener Caution . Tighten 2 N.m (18 lb in)
2Tail Lamp Assembly TIP: Upon installation, push inward on the outer edge of the tail lamp in order to seat the 2 locating pins in the body panel. prior to installing the screws.
CAUTION
Refer to Fastener Caution .

Tail Lamp Replacement (HD)

Scheme 53

Scheme 53: Tail Lamp Bulb Replacement (Chevrolet)
Scheme 53: Tail Lamp Bulb Replacement (Chevrolet)
CalloutComponent Name
Preliminary Procedure Remove the rear tail lamp. Refer to Tail Lamp Replacement (Chevrolet) , Tail Lamp Replacement (HD) , Tail Lamp Replacement (GMC) .
1Park and Turn Signal Lamp Bulb (Qty: 2)

Tail Lamp Bulb Replacement (Chevrolet)

Scheme 54

Scheme 54: Tail Lamp Bulb Replacement (GMC)
Scheme 54: Tail Lamp Bulb Replacement (GMC)
CalloutComponent Name
Preliminary Procedure Remove the rear tail lamp. Refer to Tail Lamp Replacement (Chevrolet) , Tail Lamp Replacement (HD) , Tail Lamp Replacement (GMC) .
1Park and Turn Signal Lamp Bulbs (Qty: 2)

Tail Lamp Bulb Replacement (GMC)

Exterior Lamps

The exterior lighting system consists of the following lamps

  1. The headlamps
  2. The daytime running lamps (DRL)
  3. The front fog lamps
  4. The park, tail and marker lamps
  5. The exterior courtesy lamps
  6. The turn signal/hazard lamps
  7. The stop lamps
  8. The backup lamps
  9. The cargo lamps
  10. The roof beacon lamp (if equipped)

Headlamps

The headlamps may be turned on in 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC). During ALC the headlamps will be in DRL operation in daylight conditions, or headlamp operation in low light conditions.

Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch on input circuit when the headlamp switch is in the HEAD position. When the headlamp switch is in the AUTO position, the BCM determines headlamps ON/OFF by the voltage from the ambient light sensor.

If the headlight switch is left in the ON position, the inadvertent power control feature will turn off the headlights approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain on until turned off or the battery runs dead.

The high beam indicator is illuminated when the instrument cluster receives a GMLAN serial data message from the BCM that the high beams are illuminated.

High Beams

The high beam headlamps receive voltage from the headlamp high relay located in the underhood fuse block. The BCM controls the relay on the headlamp high beam relay control circuit. High beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is grounded, the BCM grounds the headlamp high beam relay control circuit, illuminating the high beam headlamps. The right and left high beam circuits are independent and are fused independently in the underhood fuse block.

Low Beams

The low beam headlamps receive voltage from the headlamp low beam relay located in the underhood fuse block. The BCM controls the relay on the headlamp low beam relay control circuit. Low beam control is determined by a signal on the headlamp dimmer switch signal circuit from the multifunction switch. When the headlamp dimmer switch signal circuit is open, the BCM grounds the headlamp low beam relay control circuit, illuminating the low beam headlamps. The right and left low beam circuits are independent are fused independently in the underhood fuse block.

Daytime Running Lamps (DRL)

The DRL will only operate while the engine is running, for automatic transmission, the gear selector is not in the PARK position, the headlamp switch is in the AUTO position, and for manual transmission, the park brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate. The ambient light sensor is a light sensitive transistor that varies its voltage signal to the BCM in response to changes to the outside ambient light level. When the BCM receives this signal it will either turn on the dedicated DRL on the X88, the low beam headlamps only as DRL on the Z88, or the headlamps, park, and tail lamps for auto headlamp operation in low light conditions. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. The DRL can be manually turned OFF by activating the AHL/DRL switch in the headlamp switch. The AHL/DRL defeat switch sends a ground signal through the DRL switch signal circuit to the BCM. The BCM then turns OFF the DRL. When the AHL/DRL are manually turned OFF at the headlamp switch, the AHL/DRL will default to ON with the next ignition cycle. With the headlight switch in the AUTO position, the DRL will either be turned ON or OFF after an approximate 8 second delay, depending on whether daylight or low light conditions are sensed. When the BCM energizes the DRL relay, the DRL receives voltage on the DRL supply voltage circuit.

Fog Lamps

With both the ignition switch in the RUN position, and the park lamps ON, the fog lights will illuminate when the driver depresses the fog lamp switch. The BCM receives the park lamp ON signal from the interior park lamps supply voltage signal circuit. With the headlamp switch in either the park or headlamp position, and the fog lamp switch is in the ON position, the BCM will ground the fog lamp relay control circuit causing the relay to energize. The current flows from the fog lamp relay to both front fog lamps. The state of the fog lamps will remain the same until the fog lamp switch position is changed, or the ignition switch is cycled OFF and ON. Fog lamp operation will be cancelled whenever the park lamps, are turned OFF or the high beam headlights have been selected.

Park, Tail and Marker Lamps

The park, tail and marker lamps, including the license lamps, are turned on when the headlamp switch is placed in the PARK or HEAD position or anytime the headlights are requested. The underhood fuse block supplies battery positive voltage to both the park lamp relay switch contacts and the park lamp coil circuit. The BCM provides a ground or control circuit to the park lamp relay coil circuit. When the park lamps are turned ON, the BCM energizes the park lamp relay. If the headlight switch is left in the ON position, the inadvertent power control feature will turn OFF the park, tail and marker lamps approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the park, tail and marker lamps will remain on until turned OFF or the battery runs dead.

Exterior Courtesy Lamps

The BCM, driver door switch, and the passenger door switch communicate through the GMLAN serial data system. The driver door switch and passenger door switch supply power and ground to the left and right exterior lamps respectively. When the BCM commands illuminated entry, a command is also sent to the door switches for illumination of the exterior courtesy lamps. If the door locks are activated to the LOCK position, or if the ignition switch is turned to either the ON or RUN position the exterior courtesy lamps will deactivate immediately.

Turn Signal/Hazard Lamps

When the turn signal switch is placed in either the left or right position, a ground signal is completed from the turn signal switch to the BCM. When the hazard flasher switch is activated, a ground signal is completed from the turn signal/hazard switch to the BCM. The BCM then sends an ON-OFF voltage signal through the fuses to the appropriate turn signal and side repeater (export only) lamps or to all of the turn signal fuses for hazard operation. The driver door switch and passenger door switch also receive voltage from the BCM turn signal supply voltage circuits for the mirror turn signals. The door switches have no function or control of the mirror turn signals other than a pass through connection for the circuits. The audio chime is also activated when the turn signals are ON. The instrument panel cluster (IPC) receives the signals to activate the turn signal indicators over the GMLAN serial data system. When the hazard switch is pressed, all turn signal lamps will flash including both IPC turn indicators.

Stop Lamps

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-volt 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, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) control circuit. The stop lamps on this vehicle will not illuminate unless the ignition is in the accessory, run, or crank positions. When the ignition is in the OFF position the stop lamps will not illuminate when the brake pedal is applied.

Backup Lamps

The backup lamp request signal is sent from the PCM to the BCM on the GMLAN serial data system. This signal is based on the park neutral position (PNP) switch signal. The BCM supplies voltage to the backup relay and to the automatic day/night mirror when the vehicle is in reverse. The backup relay supplies a voltage on the backup lamp supply voltage circuit to the backup lamps and trailer backup circuit. The engine may need to be running for the backup lamps to function.

Cargo Lamps

The cargo lamp is controlled by the courtesy lamp supply voltage circuit. When the dimmer switch is turned clockwise to the farthest setting, the BCM receives an input from the dimmer switch for courtesy lamps and cargo lamp to be commanded ON.

Clearance Lamps

The clearance lamps, are turned ON when the headlamp switch is placed in the PARK or HEAD position or anytime the headlamps are requested. The underhood fuse block supplies battery positive voltage to both the park lamp relay switch contacts and the park lamp coil circuit. The BCM provides a ground or control circuit to the park lamps relay coil circuit. When the park lamps are turned ON, the BCM energizes the park lamp relay. If the headlamp switch is left in the ON position, the inadvertent power control feature will turn OFF the park, tail and clearance lamps approximately 10 minutes after the ignition switch is turned to the OFF position. If the driver places the headlamp switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the park, tail and marker lamps will remain ON until turned OFF or the battery runs dead.

Interior Lamps

The interior lighting consists of 2 groups. The first group includes lamps that may not be dimmed.

  1. Courtesy/illuminated entry lamps
  2. Dome lamps
  3. Map lamps
  4. Reading lamps
  5. Vanity mirror lamps

Courtesy/Illuminated Entry Lamps

The courtesy/illuminated entry lamps, may be manually turned ON or OFF by placing the interior lamp switch in the ON or OFF position. If an outside door handle is lifted and a door is opened, the courtesy/illuminated entry lamps illuminate. After all the doors have been closed the courtesy/illuminated entry lamps will remain illuminated approximately 15 seconds. The body control module (BCM) will then turn them OFF through the theater dimming feature. The courtesy/illuminated entry lamps will also turn ON prior to any door being opened, and remain illuminated approximately 40 seconds when the driver removes the ignition key. When the driver places the dome lamp defeat switch in the OFF position, the courtesy/illuminated entry lamps will be disabled.

The BCM and the door modules communicate through the GMLAN serial data circuit for the lamp illumination commands of the door switch signals. The left and right rear door latch switches are both on one circuit that is also an input to the BCM.

The left and right front door courtesy lamps (if equipped) receive voltage and ground from the driver door switch and the passenger door switch respectively. The remaining courtesy lamps are controlled and receive voltage from the BCM. Voltage for the courtesy lamp supply voltage circuit is from the INT LTS fuse in the instrument panel fuse block.

Door Sill Illumination

The door sill lighting is a dealer installed accessory. When the body control module (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.

Keyless Entry Interior Illumination

When the driver uses the door key in order to unlock the doors, the body control module (BCM) receives a door unlock signal. The BCM must have inputs or serial data messages that indicate that the ignition switch is OFF, the courtesy lamp switch is OFF and all the doors are closed. The BCM will then activate the interior lamps. The courtesy lamps will remain ON, approximately 15 seconds after the door is closed. The BCM will then turn them OFF through the theater dimming feature. If the door locks are activated to the LOCK position, or if the ignition switch is turned to either the RUN or CRANK position the courtesy lamps will turn OFF immediately.

When the driver uses the remote function actuator transmitter to unlock the doors, trunk or presses the panic button, the BCM will keep the courtesy lamps ON approximately 40 seconds. When the driver uses the remote function actuator transmitter to lock the doors, the BCM will keep the courtesy lamps on approximately 2 seconds. If the ignition switch is turned to either the RUN or CRANK position the courtesy lamps will turn OFF immediately.

Vanity Lamps

The inadvertent power supply voltage circuit of the body control module (BCM) provides battery positive voltage to each vanity mirror lamp. When the vanity mirror cover on the sunshade is opened, a switch closes to provide a ground circuit and the vanity lamp illuminates.

Reading Lamps

The inadvertent power supply voltage circuit of the body control module (BCM) provides battery positive voltage to the reading lamps. The reading lamps and switch are integral to the courtesy/reading lamp assembly. When the switch is closed, voltage is supplied and the lamp illuminates.

Battery Rundown Protection/Inadvertent Power

The body control module (BCM) inadvertent power supply voltage circuit provides battery positive voltage to all of the interior reading lamps, visor vanity mirror lamps, and cargo lamps if equipped. In the event that any of these lamps were to remain illuminated for a period of more than 10 minutes with the ignition switch in the OFF position, the BCM will deactivate the inadvertent power supply voltage circuit to prevent a total battery discharge condition.

Interior Lamps Dimming

The second interior lighting group includes lamps which may be dimmed. This group may use a combination of vacuum fluorescent (VF) illumination, LED illumination and incandescent lamps.

When the ignition switch is turned to the RUN position, the radio VF display turns ON at maximum brightness. When the park lamps are ON, all incandescent and LED back lighting turn ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time all VF displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the body control module (BCM). When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. When the I/P dimmer switch is moved from MIN to MAX, all VF displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch.

The following switches and components have back lighting when the park lamps are ON

  1. The instrument panel cluster (IPC)
  2. Window and heated seat switches
  3. Rear HVAC switches
  4. Sunroof switch
  5. Accessory switches
  6. Fog lamp switches
  7. Garage door opener
  8. Rear parking assist (RPA) disable switches
  9. Transfer case shift control switch
  10. Power take off switch
  11. Roof beacon switch
  12. Sliding rear window switch
  13. PRNDL lamps
  14. Traction control switch
  15. Steering wheel control switches
  16. Integrated trailer brake controller switch

The left and right front door switch illumination is controlled, receives voltage and ground from the driver door switch and passenger switch respectively. The radio is also a GMLAN module and has full control of its illumination. The BCM, door switches, and radio communicate through GMLAN serial data for the lamp illumination commands.

The various switches, HVAC control assembly, and the PRNDL lamps receive voltage and are controlled by the BCM on the I/P lamps dimming control circuit.

The following indicators receive voltage from the BCM and are controlled by ground from a switch or from various modules

  1. Tow indicator
  2. Transfer case control switch 4WD position indicators
  3. Fog lamp indicators
  4. Radio
  5. Analog clock
  6. HVAC control assembly
  7. Instrument panel cluster (IPC)
  8. Driver information center (DIC)
  9. Headlamp and panel dimmer switch
  10. Rear parking assist (RPA) indicator

The indicators receive voltage from the BCM on the LED dimming circuit. Control for the indicators is from the various modules or switches. Voltage for the LED dimming supply circuit, instrument panel lamps dimming control circuit and the instrument panel lamps dimming supply circuit is from the BCM.

The modules controlling the above indicators are as follows

  1. Transfer case shift control module
  2. BCM

See also:
• Diagnostic System Check - Vehicle
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
• COMPONENT CONNECTOR END VIEWS - INDEX
• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs
• Control Module References
• Diagnostic Repair Verification
• Relay Replacement (Within an Electrical Center)
• Relay Replacement (Attached to Wire Harness)
• Brake Warning Indicator Malfunction
• Door Lock and Side Window Switch Replacement - Driver Side
• Checking Aftermarket Accessories
• Backup Lamp Switch Replacement
• Turn Signal Multifunction Switch Replacement
• Front Seat Heater Switch Replacement
• Fastener Caution
• Headlamp Switch Bezel Replacement (SLT)
• Radiator Grille Replacement (GMC)
• Front Bumper Impact Bar Replacement (GMC)
• Air Cleaner Assembly Replacement
• Auxiliary Battery Replacement
• Halogen Bulb Warning
• Front Wheelhouse Liner Replacement - Left Side (GMC)
• DTC B1395
• Headlamp Replacement (HD Chevrolet Diesel)
• Headlamp Replacement (GMC)
• Brake Pedal Position Sensor Calibration
• Brake Pedal Position Sensor Replacement (Without JF4)
• Brake Pedal Position Sensor Replacement (With JF4)
• Fog Lamp Switch Replacement (with RPO SLT)
• Fog Lamp Switch Replacement (without RPO SLT)
• Fastener Tightening Specifications
• Fog Lamp Aiming