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
--- | --- | --- | --- | ---
Front Fog Lamp Switch Signal | B2740 5a | B2740 05 | B2740 05 | --
Front Fog Lamp Relay Control | B2530 00 | B2530 00 | 1 | --
Front Fog Lamp Control | 1 | 1 | 1 | --
Fog Lamp - LF Ground | -- | 1 | 1 | --
Fog Lamp - RF Ground | -- | 1 | 1 | --
Front Fog Lamp Switch Ground | -- | 2 | 2 | --
1. Front Fog Lamps Malfunction 2. Front Fog Lamp Switch Malfunction

### Circuit/System Description

The front fog lamp switch is supplied with voltage from the instrument panel cluster (IPC) via the front fog lamp switch signal circuit. The front fog lamp switch signal circuit is grounded momentarily by pressing the front fog lamp switch. The front fog lamp switch signal circuit is grounded through the switch contacts of the front fog lamp switch to a common headlamp switch ground back to the IPC. The IPC interprets the flow of voltage and responds by sending a serial data message to the underhood electrical center (UEC). The UEC responds by applying ground to the front fog lamp relay control circuit energizing the front fog lamp relay coil. With the front fog lamp relay coil energized, the relay switch contacts close allowing battery voltage to flow from the front fog lamp fuse to the front fog lamp control circuit which illuminates the front fog lamps. The left front fog lamp receives ground at G101 and the right front fog lamp is grounded at G102.

### Reference Information

#### Schematic Reference

Fog 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, park lamps ON, observe the scan tool Front Fog Lights Switch Status parameter while activating the front fog lamp switch. The parameter should change between Off and On.

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

⇒ | If the parameter changes between the commanded states, refer to Front Fog Lamps Malfunction.

### Circuit/System Testing

#### Front fog Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition OFF, verify a test lamp illuminates between B+ and the ground circuit terminal 11.

⇒ | If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPC.

3. Ignition ON, park lamps ON, verify the scan tool Front Fog Lights Switch Status parameter is Off.

⇒ | If not the specified value, test the signal circuit terminal 8 for a short to ground. If the circuit tests normal, replace the IPC.

4. Install a 3A fused jumper wire between the signal circuit terminal 8 and ground. Verify the scan tool Front Fog Lights Switch Status 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 IPC.

5. If all circuits test normal, replace the headlamp switch.

#### Front fog Lamps Malfunction

1. Ignition OFF, disconnect the front fog lamp relay.
2. Ignition ON, verify 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 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+ fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, replace the front fog lamp relay.

4. Verify a test lamp illuminates between the B+ circuit terminal 85 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 front fog lamp.
6. Ignition OFF, test for less than 5 ohms between the ground circuit terminal 1 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 front fog lamp.
8. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the front fog lamps illuminate.

⇒ | If the front fog lamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the inoperative front fog lamp.

9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. Command the Front Fog Lights 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, replace the UEC.

⇒ | If the test lamp is always OFF, replace the UEC.

11. If all circuits test normal, test or replace the front fog lamp relay.

#### Front Fog Lamp Indicator Malfunction

Ignition ON, with a scan tool perform the Front Fog Light Telltale Test for the instrument panel cluster (IPC) and observe the front fog lamp indicator.

⇒ | If the front fog lamp indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Switch Replacement

• | Front Fog Lamp Replacement

• | Relay Replacement

• | Underhood Electrical Center or Junction Block Replacement

• | Control Module References for IPC or UEC replacement, setup, and programming