Park, License, and/or Tail Lamps Malfunction

Park, License, and/or Tail Lamps Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

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.

Circuit/System Verification

1. Ignition ON, observe the scan tool parklamp switch parameter while cycling the headlamp switch between the park and off positions. The parameter should cycle between active and inactive.

^ If the parameter does not cycle between the specified values, refer to Park Lamp Switch Circuit Test.

2. Connect a test lamp between the relay side of a park lamp fuse and ground.
3. Command the parking lamps on and off with a scan tool. Verify that the test lamp turns on and off while switching between the commanded states.

^ If the test lamp does not turn on and off while changing between the commanded states, refer to the Park Lamp Relay Circuit Test.

4. If any of the park, marker, license, or tail lamps do not turn on and off, refer to the Exterior Lamp Circuit Test.

Circuit/System Testing

Park Lamp Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition OFF, test for less than 1.0 ohm of resistance 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 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool BCM 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 switch.

Park Lamp Relay Circuit Test

1. Ignition OFF, disconnect the park lamp relay.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

^ If the test lamp does not illuminate, replace the underhood fuse block.

3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 86 and ground.

^ If the test lamp does not illuminate, replace the underhood fuse block.

4. Connect a test lamp between the relay control circuit terminal 85 and the B+ circuit terminal 86.
5. 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 relay control circuit for a short to ground. If the circuit tests normal, replace the BCM.

^ If the test lamp is always OFF, test the relay control 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 park lamp relay.

Exterior Lamps Circuit Test

1. Ignition OFF, disconnect the harness connector at an affected park, marker, license, or tail lamp.
2. Verify that a test lamp illuminates when connected between battery voltage and the listed ground circuit terminal.

* Front park lamp terminal G
* Tail lamp terminal GRD
* Marker and clearance lamps terminal A
* License lamp terminal B

^ If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, connect a test lamp between the listed control circuit terminal and ground.

* Front park lamp terminal MAJ
* Tail lamp terminal MNR
* Marker and clearance lamps terminal B
* License lamp terminal A

4. 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.

5. If all circuits test normal, test or replace the affected lamp.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Park/Turn Signal Lamp Bulb Replacement (Chevrolet) Park/Turn Signal Lamp Bulb Replacement (GMC)
* Rear License Lamp Replacement (VF7) Rear License Lamp Replacement (Silverado)
* Tail Lamp Bulb Replacement (GMC) Tail Lamp Bulb Replacement (Chevrolet)
* Headlamp Switch Replacement (without RPO SLT) Headlamp Switch Replacement (with RPO SLT)