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Park, License, and/or Tail Lamps Malfunction



Park, License, and/or Tail Lamps Malfunction

Diagnostic Instructions

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



Diagnostic Fault Information






Circuit/System Description

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 G201 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.


Reference Information
Schematic Reference

Exterior Lights Schematics (Exterior Lights Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


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. Test for less than 1.0 ohm 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 the appropriate park, marker, license, or tail lamp.
2. Verify that a test lamp illuminates when connected between B+ 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 appropriate lamp.



Repair Instructions

Perform theDiagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Parking and Turn Signal Lamp Bulb Replacement (Chevrolet) ()Parking and Turn Signal Lamp Bulb Replacement (GMC) (Service and Repair)
* Rear License Plate Lamp Replacement (Silverado) (Rear License Plate Lamp Replacement (Silverado))Rear License Plate Lamp Replacement (VF7) (Rear License Plate Lamp Replacement (VF7))
* Tail Lamp Bulb Replacement (Chevrolet) ()Tail Lamp Bulb Replacement (GMC) ()
* Headlamp Switch Replacement (with RPO SLT) (Headlamp Switch Replacement (with RPO SLT))Headlamp Switch Replacement (without RPO SLT) (Headlamp Switch Replacement (without RPO SLT))
* Control Module References (Programming and Relearning) for BCM replacement, programming, and setup.


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