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, marker, license, and clearance (Y92 only) lamps are turned on when the headlamp switch is placed in the PARK or ON position or anytime the headlights are requested. The I/P BATT fuse in the engine wiring harness junction block supplies battery positive voltage to both the park lamp relay switch contacts and the park lamp coil circuit. The body control module (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. Current flow is from the park lamp relay to the individual park lamp circuit fuses and to their respective park, tail, marker, and license lamps. The front park and marker lamps are grounded at G107 and G103. The tail lamps are grounded at G401 and G402. The license lamps are grounded at G401. When equipped with the Y92 roof rack option, the clearance lamps are grounded at G302. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, the park, tail, marker, license, and clearance 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 Headlamp Switch Circuit Test.

2. Command the parking lamps on and off with a scan tool. Verify the park, license, and tail lamps turn on and off.

^ If any of the lamps do not cycle between the commanded states, refer to Exterior Lamps Circuit Test.

Circuit/System Testing

Headlamp Switch Circuit Test

1. Ignition OFF, disconnect the harness connector X1 at the headlamp switch.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal C and ground.

^ If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool BCM parklamp 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. Install a 3A fused jumper wire between the signal circuit terminal E 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.

Exterior Lamps Circuit Test

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

* Front park lamp terminal A
* Rear park lamp terminal E
* Marker or 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 B
* Rear park lamp Chevy or Isuzu terminal A
* Rear park lamp GMC terminal C
* Marker or license lamp terminal A

4. Turn the park lamp switch on and off and verify that the test lamp turns on an off.

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

^ If the test lamp remains illuminated test the control circuit for a short to voltage.

5. If all circuits test normal replace the affected bulb.

Repair Instructions

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

* Park/Turn Signal/Side Marker Lamp Bulb Replacement (Envoy) Park/Turn Signal/Side Marker Lamp Bulb Replacement (TrailBlazer)
* Tail Lamp Bulb Replacement
* Rear License Lamp Replacement