Park, License, and/or Tail Lamps Malfunction (Front LED Park/Marker Lamps with T4Q)
Park, License, and/or Tail Lamps Malfunction (Front LED Park/Marker Lamps with T4Q)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
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. The Headlamp and Panel Dimmer 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 battery voltage to flow through the LT PRK fuses and RT 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 (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Ignition ON, observe the scan tool Parking Lamp Switch parameter while cycling the park lamp switch ON and OFF. The readings should toggle between Active and Inactive.
• If the readings do not change between the commanded states, refer to Park Lamp Switch Malfunction.
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, License, and/or Tail Lamps Malfunction.
3. Command the Parking Lamps ON and OFF with a scan tool. The front LED park lamps should turn ON and OFF when changing between the commanded states.
• If the front LED park lamps do not turn ON and OFF when commanded, refer to Front LED Park Lamps Malfunction.
Circuit/System Testing
Park Lamp 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 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 Park Lamp 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 Park Lamp 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, License, and/or Tail 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 86 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the park lamp relay.
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/license/marker lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohm between the appropriate ground circuit terminal listed below and ground.
* Headlamp - Left or Right terminal J
* Tail Lamp Circuit Board - Left or Right Rear terminal D - with Z75 + E52
* License lamp terminal B
• If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the park/license/marker lamp.
8. Connect a 15 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the park/marker lamps illuminate.
• If the park/marker lamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the park/license/marker lamp.
9. Connect a test lamp between the control circuit terminal 85 and B+ 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.
Front LED Park Lamps Malfunction
1. Ignition OFF, disconnect the PRK 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. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the park lamp relay.
4. 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 an open/high resistance.
5. Disconnect the harness connector at the inoperative headlamp/park lamp assembly.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohm between the ground circuit terminal J and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the inoperative headlamp/park lamp assembly.
8. Connect a 20 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the marker lamps illuminate.
• If all of the front park/marker lamp LEDs do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the headlamp control module.
• If some of the front park/marker lamp LEDs illuminate, replace the appropriate headlamp assembly.
9. Connect a test lamp between the control circuit terminal 85 and B+ circuit terminal 86.
10. Command the Park 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.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
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* Rear License Plate Lamp Replacement (GMC Denali) (Rear License Plate Lamp Replacement (GMC Denali))Rear License Plate Lamp Replacement (Escalade) (Rear License Plate Lamp Replacement (Escalade))Rear License Plate Lamp Replacement (Yukon Two-mode Hybrid) (Rear License Plate Lamp Replacement (Yukon Two-mode Hybrid))
* Tail Lamp Replacement (Avalanche) (Tail Lamp Replacement (Avalanche))Tail Lamp Replacement (GMC Yukon Two-Mode Hybrid) (Tail Lamp Replacement (GMC Yukon Two-Mode Hybrid))Tail Lamp Replacement (Chevrolet Tahoe Two-Mode Hybrid) (Tail Lamp Replacement (Chevrolet Tahoe Two-Mode Hybrid))Tail Lamp Replacement (Cadillac) (Tail Lamp Replacement (Cadillac))Tail Lamp Replacement (Tahoe, Yukon) (Tail Lamp Replacement (Tahoe/Yukon))
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Programming and Relearning) for BCM or headlamp control module replacement, setup, and programming