Lighting System: Diagnosis Chevrolet Silverado Classic 1500

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Begin the system diagnosis with the Diagnostic System Check - Vehicle . The Diagnostic System Check will provide the following information

1. The identification of the control modules which command the system
2. The ability of the control modules to communicate through the serial data circuit
3. The identification of any stored diagnostic trouble codes (DTCs) and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Output Controls

Body Control Module (BCM)

Driver Door Module (DDM)/Passenger Door Module (PDM)

Scan Tool Data List

Body Control Module (BCM)

Engine Control Module (ECM)

Driver Door Module (DDM)

Passenger Door Module (PDM)

Instrument Panel Cluster Module (IPC)

Circuit Description

The body control module (BCM) supplies battery positive voltage to the individually controlled lamps. In the event that any of these lamps were to remain illuminated for more than 20 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.

Voltage for the inadvertent power supply voltage circuit is from the TBC 2C fuse in the instrument panel (I/P) fuse block directly through the BCM to this circuit.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC B1480 Battery Rundown Protection Circuit

Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

1. The inadvertent power supply voltage circuit is shorted to ground for more than 1 second.
2. There is a loss of the instrument panel fuse block TBC 2C battery supply voltage to the BCM for 1 second while one or more of the lamps in the inadvertent power circuit has been activated.

Action Taken When the DTC Sets

The lamps on the inadvertent power supply voltage circuit will not operate.

Conditions for Clearing the MIL/DTC

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

Diagnostic Aids

1. Perform a visual inspection for loose or poor connections at all related components. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .
2. A short to ground in the inadvertent power supply voltage circuit or the battery positive voltage circuit will cause the TBC 2C fuse to open.

The body control module (BCM) monitors the front fog lamp switch signal circuit in order to determine when the fog lamp relay is to be energized. When the BCM senses that the front fog lamp switch signal circuit is grounded momentarily by pressing the fog lamp switch, the BCM energizes the fog lamp relay by grounding the fog lamp relay control circuit.

This diagnostic procedure supports the following DTC

DTC B2527 Front Fog Lamps Circuit Low

The battery voltage must be between 9-16 volts.

When the front fog lamp switch signal circuit is shorted to ground for approximately 15 seconds

The fog lamps will not operate.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

1. Test the fog lamp switch for sticking in the ON position.
2. Perform a visual inspection for loose or poor connections at all related components. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .

DTC B2527

The body control module (BCM) monitors the rear fog lamp switch signal circuit in order to determine when the rear fog lamp relay is to be energized. When the BCM senses that the rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch, the BCM energizes the rear fog lamp relay by grounding the rear fog lamp relay control circuit.

This diagnostic procedure supports the following DTC

DTC B2537 Rear Fog Lamps Circuit Low

The battery voltage must be between 9-16 volts.

When the rear fog lamp switch signal circuit is shorted to ground for approximately 15 seconds.

The rear fog lamps will not operate.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

1. Test the rear fog lamp switch for sticking in the ON position.
2. Perform a visual inspection for loose or poor connections at all related components. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .

DTC B2537

When the body control module (BCM) receives a signal requesting to illuminate the backup lamps, battery voltage is sent directly from the BCM through the backup lamp supply voltage circuit to the backup lamps.

Voltage for the backup lamp supply voltage circuit as well as the courtesy lamp supply voltage circuit is from the left instrument panel fuse block TBC 2B 15-amp fuse directly through the BCM to these circuits.

This diagnostic procedure supports the following DTC

DTC B2550 Backup Lamps Control Circuit

The battery voltage must be between 9-16 volts.

1. When the BCM receives a backup lamp request signal and the backup lamp supply voltage circuit is shorted to ground
2. When the BCM is not receiving a backup lamp request signal and the backup lamp supply voltage circuit is open or shorted to voltage
3. There is a loss of the instrument panel fuse block TBC 2B battery supply voltage to the BCM for 1 second.

The backup lamps will not operate.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

1. Perform a visual inspection for loose or poor connections at all related components. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .
2. A short to ground on the backup lamp supply voltage circuit, courtesy lamp supply voltage circuit OR the TBC 2B battery positive voltage circuit to the BCM will open the TBC 2B fuse in the left instrument panel fuse block.

When the body control module (BCM) senses a request for low beam headlamp illumination, the BCM sends a ground signal to the low beam headlamp relay through the headlamp low beam relay control circuit. The headlamp low beam relay will apply voltage to illuminate the headlamps.

This diagnostic procedure supports the following DTC

DTC B2575 (Left or generic) Headlamp Control Circuit

The battery voltage must be between 9-16 volts.

1. When the BCM receives a command to illuminate the low beam headlamps and the headlamp low beam relay control circuit is open or shorted to voltage
2. When the BCM does not receive a command to illuminate the low beam headlamps and the headlamp low beam relay control circuit is shorted to ground
3. When the low beam relay coil side is open or the battery positive voltage to the low beam relay is open

The low beam headlamps will not operate or will remain always on.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

When the body control module (BCM) receives a ground signal from the multifunction high beam or flash to pass (FTP) switch commanding to illuminate the high beam headlamps, the BCM will energize the high beam relay by grounding the high beam relay control circuit.

This diagnostic procedure supports the following DTC

DTC B2580 (Left or generic) Headlamp High Beam Control Circuit

The battery voltage must be between 9-16 volts.

1. When the BCM receives a high beam headlamp OFF command and the high beam headlamp relay control circuit is shorted to ground
2. When the BCM receives a high beam headlamp ON command and the high beam headlamp relay control circuit is shorted to voltage or open
3. When the high beam relay coil side is open or the battery positive voltage to the high beam relay is open

The high beam headlamps will not operate or will remain always on.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

When the body control module (BCM) receives a ground signal from the headlamp switch commanding to illuminate the park lamps, the BCM will energize the park lamp relay by grounding the park lamp relay control circuit.

This diagnostic procedure supports the following DTC

DTC B2585 (Left or generic) Park Lamp Control Circuit

The battery voltage must be between 9-16 volts.

1. When the park lamp relay control circuit is open or shorted to ground
2. When the BCM receives a park lamp ON command and the park lamp relay control circuit is shorted to voltage
3. When the park lamp relay coil side is open or the battery positive voltage to the low beam relay is open

The park lamps will not operate or will remain always on.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

The ambient light sensor is a light sensitive transistor that sends a variable voltage signal to the body control module (BCM) in response to the exterior light level. The BCM energizes the daytime running lights (DRL) relay by grounding the DRL relay control circuit. The DRL operate when the ambient light sensor indicates daytime, the ignition switch is in the RUN position and the gear selector is not in the park position.

This diagnostic procedure supports the following DTC

DTC B2600 Daytime Running Lamp Control 1 (left or system) Circuit

The battery voltage must be between 9-16 volts.

1. When the BCM sends a DRL OFF command and the DRL relay control circuit is shorted to ground
2. When the BCM sends a DRL ON command and the DRL relay control circuit is shorted to voltage or open

The DRL will not operate or will remain always on.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

The body control module (BCM) receives a variable voltage signal from the instrument panel (I/P) dimmer switch requesting to illuminate the illumination lamps to a desired intensity. When this occurs, the BCM directly sends a variable voltage based on the I/P dimmer switch position on the instrument panel lamps dimming supply voltage circuit, instrument panel lamps dimming control circuit, and the LED dimming signal circuit.

Voltage for the instrument panel lamps dimming supply voltage circuit, instrument panel lamps dimming control circuit, and the LED dimming signal circuits is from the TBC 2 A fuse in the instrument panel fuse block directly through the BCM to these circuits.

This diagnostic procedure supports the following DTC

DTC B2610 Passenger Compartment Dimming 1 (cluster, etc.) Circuit

The battery voltage must be between 9-16 volts.

1. The instrument panel lamps dimming control circuit is open, shorted to ground, or shorted to voltage.
2. The instrument panel lamps dimming supply voltage circuit is open, shorted to ground, or shorted to voltage.
3. There is a loss of the instrument panel fuse block TBC 2 A battery supply voltage to the BCM for 1 second.

The illumination lamps will not operate or are always ON.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

1. Perform a visual inspection for loose or poor connections at all related components. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .
2. A short to ground in the following circuits will cause the TBC 2 A fuse to open: The instrument panel lamps dimming control. Battery positive voltage from the instrument panel fuse block TBC 2 A fuse.
3. An open in the TBC 2 A fuse will cause the BCM to set the following DTC: B0951 B2610 B2625

The body control module (BCM) receives a ground signal from the door jamb, liftglass/liftgate if equipped, or courtesy lamp switches requesting courtesy/dome lamp illumination. When this occurs, the BCM directly sends a voltage through the courtesy lamp supply voltage circuit illuminating the courtesy/dome lamps.

Voltage for the courtesy lamp supply voltage circuit as well as the backup lamp supply voltage circuit is from the left instrument panel fuse block TBC 2B 15-amp fuse directly through the BCM to these circuits.

This diagnostic procedure supports the following DTC

DTC B2615 Passenger Compartment Dimming 2 (Courtesy Lamps, etc.) Circuit

The battery voltage must be between 9-16 volts.

1. When the BCM receives a courtesy lamp illumination request signal and the courtesy lamp supply voltage circuit is shorted to ground
2. When the BCM is not receiving a courtesy lamp illumination request signal and the courtesy lamp supply voltage circuit is open only to the first splice from the BCM or the circuit is shorted to voltage
3. There is a loss of the instrument panel fuse block TBC 2B battery supply voltage to the BCM for 1 second.

The courtesy dome lamps will not operate or are always ON.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

1. Perform a visual inspection for loose or poor connections at all related components. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .
2. An open circuit up to the first splice only, from the BCM, will set the DTC.
3. A short to ground on the backup lamp supply voltage circuit, courtesy lamp supply voltage circuit OR the TBC 2B battery positive voltage circuit to the BCM will open the TBC 2B fuse in the left instrument panel fuse block.

The body control module (BCM) directly sends a 5-volt reference voltage to the instrument panel (I/P) dimmer switch which is then adjusted based on the I/P dimmer switch position and returned as a dimming return and dimming input to the BCM. The BCM uses this signal to directly control the desired level of instrument panel illumination lamp intensity.

This diagnostic procedure supports the following DTC

DTC B2620 Display Dimming Pulse Width Modulation (PWM) Input Circuit

The battery voltage must be between 9-16 volts.

1. The BCM monitors a dimming return voltage of less than 4.5 volts.
2. The BCM monitors a 5-volt reference voltage of greater than 5.5 volts.
3. The BCM monitors dimming input voltage of equal or greater than 4.86 volts for more than 1 second.

The instrument panel illumination lamp dimming will not operate.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

The body control module (BCM) receives a variable voltage signal from the instrument panel (I/P) dimmer switch requesting to illuminate the dimming lamps to a desired intensity. When this occurs, the BCM directly sends a pulse width modulated (PWM) voltage based on the I/P dimmer switch position on the LED dimming supply circuit, instrument panel lamps dimming control circuit, and the instrument panel lamps dimming supply voltage circuit.

Voltage for the LED dimming supply circuit, instrument panel lamps dimming control circuit, and the instrument panel lamps dimming supply voltage circuit is from the TBC 2 A fuse in the I/P fuse block directly through the BCM to these circuits.

This diagnostic procedure supports the following DTC

DTC B2625 Display Dimming Pulse Width Modulation (PWM) Output Circuit

The battery voltage must be between 9-16 volts.

1. The instrument panel lamps dimming control circuit is shorted to ground.
2. The LED dimming supply circuit is shorted to ground.
3. There is a loss of the I/P fuse block TBC 2 A fuse battery supply voltage to the BCM for 1 second.

All dimming lamps will not illuminate or the control switch ON/OFF indicators will not illuminate.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

1. Perform a visual inspection for loose or poor connections at all related components. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .
2. A short to ground in the following circuits will cause the TBC 2 A fuse to open. The instrument panel lamps dimming control. Battery positive voltage from the I/P fuse block TBC 2 A fuse.
3. An open in the TBC 2 A fuse will cause the BCM to set the following DTC: B0951 B2610 B2625

The body control module (BCM) monitors the ambient light sensor signal circuit in order to determine if the daytime running lights (DRL) or the auto headlights (ALC) should be turned ON in the AUTO mode. When the BCM senses the ambient light sensor signal voltage is between 1.75-4.9 volts, either the DRL will be commanded ON or the ALC will be commanded ON depending upon the amount of light received by the sensor.

This diagnostic procedure supports the following DTC

DTC B2645 Ambient Light Sensor Circuit

The system voltage must be between 9-16 volts.

1. When the ambient light sensor signal voltage is less than 1.75 volts.
2. When the ambient light sensor signal voltage is more than 4.9 volts.

The ALC will remain ON in any ambient light state.

1. This DTC will clear immediately after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. Use a scan tool in order to clear history and current DTCs.

The body control module (BCM) monitors the courtesy lamp switch signal circuit in order to determine when the courtesy/dome lamps should be illuminated. When the BCM senses that the courtesy lamp switch signal circuit is grounded when the switch is activated, the BCM will illuminate the courtesy/dome lamps.

This diagnostic procedure supports the following DTC

DTC B3801 Passenger Compartment Lamp Request Circuit

1. The BCM instrument panel dimmer switch reference voltage must be between 4.5-5.5 volts.
2. The battery voltage must be between 9-16 volts.

1. When the instrument panel dimmer switch signal is greater than 1 volt.
2. When the BCM receives a courtesy lamp ON request signal from the courtesy lamp switch.

The courtesy/dome lamps will not operate.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

1. Test the courtesy lamp switch for sticking in the ON position.
2. Perform a visual inspection for loose or poor connections at all related components. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .

DTC B3801

The body control module (BCM) monitors the park lamp switch on signal circuit and the headlamp switch headlamps on signal circuit in order to determine when the park lamps and headlamps should be illuminated. When the headlamp switch is turned to PARK, the BCM senses that the park lamp switch signal on circuit is grounded and the headlamps switch headlamps ON signal circuit is open. The BCM will then energize the park lamp relay illuminating the park lamps. When the headlamp switch is turned to HEAD, the BCM senses that the park lamp switch on signal circuit and the headlamp switch headlamps ON signal circuit are grounded. The BCM will then energize the park lamp relay and headlamp low beam relay or high beam relay illuminating the park lamps and headlamps.

This diagnostic procedure supports the following DTC

DTC B3802 Park Lamps Request Circuit

The battery voltage must be between 9-16 volts.

1. The headlamp switch park lamps ON signal circuit is open or has a high resistance.
2. The headlamp switch headlamps ON signal circuit is shorted to ground.

The park lamps will not operate or the headlamps will illuminate without the park lamps.

1. This DTC will clear on current status after the condition for setting the fault is corrected.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History and current DTCs can be cleared using a scan tool.

DTC B3802

The engine control module (ECM) monitors the stop lamp switch signal circuit and the torque converter clutch (TCC) brake switch/cruise control release signal circuit every 100 ms. The ECM monitors the status of the stop lamp switch signal circuit and the TCC brake switch/cruise control signal circuit to see if they match when the brake pedal is pressed or released.

This diagnostic procedure supports the following DTC

DTC P0504 Brake Switch Circuit 1-2 Correlation

The ignition is ON.

The status of the stop lamp switch input to the ECM, and the TCC brake switch/cruise control input to the ECM do not match for at least 2 seconds continuously, for 10 occurrences. Each time the signals match then do not match a counter increments. When the counter reaches 10 the DTC will set.

When DTC P0504 is set the following will occur

1. The cruise control is disabled.
2. The ECM will function as if the brake pedal is not pressed.
3. The control module stores the DTC information into memory when the diagnostic runs and fails.
4. The malfunction indicator lamp (MIL) will not illuminate.
5. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.

Conditions for Clearing the DTC

1. The DTC will clear when the status of the stop lamp switch input to the ECM, and the TCC brake switch/cruise control input to the ECM match for at least 2 seconds continuously for both the pressed position and the released position.
2. A current DTC Last Test Failed clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
4. Clear the DTC with a scan tool.

1. Aftermarket trailer brake controllers must be disconnected before diagnosing DTC P0504 due to they could result in incorrect diagnostics.
2. Check for intermittents and poor connections. Refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .

DTC P0504

1. Perform the «Diagnostic System Check - Vehicle»(ref-277883-S07139257572008012100000) 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»(ref-277846-S16318691572008012100000) «Interior Lighting Systems Description and Operation»(ref-277846-S15638476362008012100000)

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the Lighting System. Refer to «Checking Aftermarket Accessories»(ref-277884-S30236091172008012100000) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Symptom List

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

1. «Backup Lamps Always On»(ref-277846-S07538136642008012100000)
2. «Backup Lamps Inoperative»(ref-277846-S15358174552008012100000)
3. «Cargo Lamp Always On»(ref-277846-S22251405322008012100000)
4. «Cargo Lamp Inoperative»(ref-277846-S00858332902008012100000)
5. «Clearance Lamps Inoperative»(ref-277846-S28627645812008012100000)
6. «Courtesy Lamps Always On»(ref-277846-S22661376822008012100000)
7. «Courtesy Lamps Inoperative»(ref-277846-S18633268112008012100000)
8. «Daytime Running Lamps (DRL) Always On»(ref-277846-S39704281812008012100000)
9. «Daytime Running Lamps (DRL) Defeat Inoperative»(ref-277846-S18370983342008012100000)
10. «Daytime Running Lamps (DRL) Inoperative»(ref-277846-S06379266742008012100000)
11. «Exterior Courtesy Lamp(s) Always On»(ref-277846-S21597209042008012100000)
12. «Exterior Courtesy Lamp(s) Inoperative»(ref-277846-S30417094052008012100000)
13. «Fog Lamp Indicator Inoperative»(ref-277846-S12718938492008012100000)
14. «Fog Lamps Always On»(ref-277846-S09013949522008012100000)
15. «Fog Lamps Inoperative»(ref-277846-S36458866262008012100000)
16. «Hazard Lamps Always On»(ref-277846-S35522206672008012100000)
17. «Hazard Lamps Inoperative»(ref-277846-S07063088372008012100000)
18. «Headlamp Low or High Beams Always On»(ref-277846-S36840987062008012100000)
19. «Headlamps Inoperative - High Beams»(ref-277846-S28438590752008012100000)
20. «Headlamps Inoperative - Low Beams»(ref-277846-S25280455422008012100000)
21. «Low and High Beams Headlamps Inoperative»(ref-277846-S13231128992008012100000)
22. «Headlamps Flash to Pass Inoperative»(ref-277846-S27378365562008012100000)
23. «High Beam Indicator Always On»(ref-277846-S34398820512008012100000)
24. «High Beam Indicator Inoperative»(ref-277846-S26961321422008012100000)
25. «Interior Backlighting Does Not Dim»(ref-277846-S27123722702008012100000)
26. «Interior Backlighting Inoperative»(ref-277846-S08606009422008012100000)
27. «Park, License, and Tail Lamps Always On»(ref-277846-S29922246472008012100000)
28. «Park, License, and Tail Lamps Inoperative»(ref-277846-S26291111732008012100000)
29. «Reading Lamp(s) Inoperative»(ref-277846-S19472868142008012100000)
30. «Roof Beacon Lamp Always On»(ref-277846-S29015709632008012100000)
31. «Roof Beacon Lamp Inoperative»(ref-277846-S38715817302008012100000)
32. «Stop Lamps Always On»(ref-277846-S20369447552008012100000)
33. «Stop Lamps Inoperative»(ref-277846-S15534150652008012100000)
34. «Turn Signal Lamps and/or Indicators Always On or Flashing»(ref-277846-S37451396372008012100000)
35. «Turn Signal Lamps and/or Indicators Inoperative»(ref-277846-S36305441412008012100000)
36. «Vanity Mirror Lamp(s) Inoperative»(ref-277846-S04297049992008012100000)