For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | 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 | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Park Lamp Relay B+ | 1 | 1 | -- | --
Park Lamp Switch ON Signal | 2 | B257A 00 | 2 | --
Park Lamp Relay Control | 1 | 1 | B2585 00 | --
License Lamp Control | 1 | 1 | 1 | --
Park Lamp Control | 1 | 1 | 1 | --
License Lamp Ground | -- | 1 | -- | --
Park Lamps - LF Ground | -- | 1 | -- | --
Park Lamps - RF Ground | -- | 1 | -- | --
Tail/Stop Lamp - Left Ground | -- | 1 | -- | --
Tail/Stop Lamp - Right Ground | -- | 1 | -- | --
Headlamp And Panel Dimmer Switch Ground | -- | 2 | -- | --
1. Park, License, and/or Tail Lamps Malfunction 2. Park Lamp Switch Malfunction

### Circuit/System Description

Battery voltage is applied at all times to both the coil and switch sides of the PRK LAMP relay located in the underhood fuse block. The headlamp and panel dimmer switch is suppled 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 battery voltage to flow through the LT PRK and RT PRK fuses to all of the park, tail, and license lamps.

### Reference Information

#### Schematic Reference

Exterior Lights Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Exterior Lighting Systems Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Ignition ON, observe the scan tool Park Lamp Switch parameter while turning the headlamp and panel dimmer switch to the PARK and AUTO positions. The parameter should change between On and Off.

⇒ | If the parameter does not change between the commanded states, refer to Park Lamp Switch Malfunction.

⇒ | If the parameter changes between the commanded states, refer to Park, License, and/or Tail 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, test for less than 5 ohms between the ground circuit terminal 4 and ground.

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

3. Ignition ON, verify the scan tool Park Lamp Switch parameter is Off.

⇒ | If not the specified value, test the signal circuit terminal 5 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 5 and ground. Verify the scan tool Park Lamp Switch parameter is On.

⇒ | If not the specified value, test the signal 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 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 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 park/license lamp.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit 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 park/license lamp.
8. Connect a 20A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the park/license lamps illuminate.

⇒ | If the park/license lamps do not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the inoperative park/license lamp.

9. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
10. Command the Parking light Test 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 after completing the diagnostic procedure.

• | Headlamp Switch Replacement

• | Rear License Plate Lamp Replacement

• | Parking and Turn Signal Lamp Replacement

• | Tail Lamp Assembly and /or Backup, Sidemarker, Stop, Turn Signal Bulb Replacement

• | Relay Replacement

• | Control Module References for BCM replacement, setup, and programming