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 through a resistor 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 cluster requesting the instrument cluster 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

1. 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.

⇒ | If the parameter does not cycle between the specified values, refer to Rear Fog Lamp Switch Malfunction.

2. Ignition ON, perform the scan tool Rear Fog Lamps Relay Command. Verify the rear fog lamps turn ON and OFF.

⇒ | If the rear fog lamps do not cycle between the commanded states, refer to Rear Fog Lamp Malfunction.

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

⇒ | If the rear fog indicator do not cycle between the commanded states, refer to Rear Fog Indicator Malfunction

### Circuit/System Testing

#### Rear Fog Lamp Switch 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 Lamp Malfunction

1. Ignition OFF, disconnect the appropriate harness connector at the tail lamp listed below:

• | E29LR Fog Lamp - Left Rear

• | E29RR Fog Lamp - Right Rear

2. Test for less than 5 Ω between the appropriate ground circuit harness connector terminal listed below and ground:

• | E29LR Fog Lamp - Left Rear harness connector terminal 2

• | E29RR Fog Lamp - Right Rear harness connector terminal 2

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

3. Connect a test lamp between the appropriate control circuit harness connector terminal listed below and ground :

• | E29LR Fog Lamp - Left Rear harness connector terminal 1

• | E29RR Fog Lamp - Right Rear harness connector terminal 1

4. Ignition ON, perform the Rear Fog Lamps Relay Command test. The test lamp should be ON/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 circuit tests normal, replace the K9 Body Control Module (BCM).

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the K9 Body Control Module (BCM).

5. If all circuits test normal, test or replace the appropriate tail lamp.

#### Rear Fog Indicator Malfunction

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).

### 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.