For 1990-2009 cars

### Diagnostic Instructions

1. Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
2. Review Strategy Based Diagnosis for an overview of the diagnostic approach.
3. 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
--- | --- | --- | --- | ---
Headlight Switch 12 V Reference | 1 | 1 | 1 | --
Headlight Switch Signal | 1 | 1 | 2 | --
1. Rear Fog Lamps inoperative 2.Rear Fog Lamps always on

### Circuit/System Description

The rear fog lamp switch signal circuit is grounded momentarily by pressing the rear fog lamp switch. The body control module (BCM) energizes the rear fog lamp supply voltage circuit which illuminates the rear fog lamp. With the rear fog lamp switch activated the BCM sends a message via serial data to the instrument panel cluster (IPC) requesting the instrument panel cluster (IPC) to illuminate the rear fog indicator.

### 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, perform the scan tool Rear Fog Lamps Switch parameter. The reading should change between Active/Inactive when changing between pressed and released rear fog lamp switch button.

• | Ignition ON, perform the instrument cluster All Indicators test ON and OFF test. The rear fog indicator should be ON / OFF.

### Circuit/System Testing

#### Rear Fog Lamp Malfunction

1. Ignition OFF, disconnect the X1 and X3 harness connector at the K9 Body Control Module (BCM).
2. Test for less than 0.3 V between the 12 V reference circuit terminal 4 at the X3 harness connector and ground.

⇒ | If greater than the specified value, test the 12 V Reference circuit for an short to voltage.

3. Test for less than 0.3 V between the signal circuit terminal 9 at the X1 harness connector and ground.

⇒ | If greater than the specified value, test the signal circuit for an short to voltage.

4. Test for infinite resistance between the signal circuit terminal 9 at the X1 harness connector and ground.

⇒ | If less than the specified value, test the signal circuit for an short to ground.

5. Test for infinite resistance between the 12 V reference circuit terminal 4 at the X3 harness connector and ground.

⇒ | If less than the specified value, test the 12 V reference circuit for an short to ground.

6. Press and hold the rear fog lamp switch button.
7. Test for 80-120 Ω between the signal circuit terminal 9 at the X1 harness connector and the 12 V reference circuit terminal 4 at the X3 harness connector.

⇒ | If not within the specified range, test the 12 V reference circuit and the signal circuit for an open/high resistance. If the circuit test normal replace the S30 Headlamp Switch.

8. If all circuit test normal, replace the K9 Body Control Module (BCM).

#### Rear Fog Indicator Malfunction

1. Ignition ON, command the instrument cluster All Indicators test ON and OFF with the scan tool. The rear fog indicator lamp should be ON / OFF when changing between the commanded states.

⇒ | If the rear fog indicator stays always on or always off, replace the P16 Instrument Panel Cluster (IPC).

⇒ | If the rear fog indicator is changing between ON and OFF, replace the K9 Body Control Module (BCM).

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Tail Lamp Replacement

• | Control Module References for BCM or instrument panel cluster replacement, setup and programming.