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.
Diagnostic Fault Information
Circuit/System Description
The vehicle park, license, and tail lamps are controlled by the body control module (BCM) based on an input from the headlamp switch. The headlamp switch has four positions: Off, Auto, Park, and Headlamps. The default headlamp switch position is Auto, in which the BCM uses the ambient light sensor to determine when exterior lamps are needed. The Off portion of the headlamp switch is a momentary switch which overrides the automatic lamps and will turn off the vehicle lamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The Headlamp position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the Park position, the park lamp switch on signal circuit is grounded, prompting the BCM to turn on the exterior lamps, regardless of other factors such as ambient light.
When a park lamp request is received, the BCM grounds the park lamp relay control circuit. This energizes the PRK LAMP Relay and battery voltage is applied through the exterior lamp fuses illuminating the park, license, tail and marker lamps.
Circuit/System Verification
1. Ignition ON, observe the scan tool BCM 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 Malfunction.
2. Command the Parking Lamps ON and OFF with a scan tool. Verify the park, license, and tail lamps turn ON and OFF.
• If all of the park, license, and tail lamps are always OFF, refer to the Park Lamp Relay Test.
• If any of the lamps do not cycle between the commanded states, refer to Exterior Lamps Circuit Malfunction.
Circuit/System Testing
Headlamp Switch Circuit Malfunction
1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 8 and B+.
• If the test lamp does not illuminate, 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 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 Parklamp Switch parameter is Active.
• If not the specified value, test the signal circuit for a short to voltage or and 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 Test
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 circuits for a short to voltage.
3. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
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. Connect a test lamp between the control circuit terminal 86 and B+.
6. 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.
7. If all of the circuits test normal, test or replace the park lamp relay.
Exterior Lamps Circuit Malfunction
1. Ignition OFF, disconnect the harness connector at the inoperative exterior lamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Connect a test lamp between the inoperative lamp control circuit terminal and ground.
4. Ignition ON, 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 voltage.
• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance.
5. If all circuits test normal, test or replace the lamp bulb.
Component Testing
Headlamp Switch
1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for less than 2.0 ohms of resistance between the signal terminal 2 and the ground terminal 8 with the switch in the Park position.
• If not the specified value, replace the headlamp switch.
3. Test for less than 2.0 ohms of resistance between the signal terminal 2 and the ground terminal 8 with the switch in the Headlamp position.
• If not the specified value, replace the headlamp switch.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Headlamp Switch Replacement
* Headlamp Bulb Replacement
* Parking and Turn Signal Lamp Replacement
* Tail Lamp Replacement
* Rear License Lamp Replacement
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)