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.

### DTC Descriptors

DTC B2740 05: Front Fog Lights Switch Circuit Open or High Voltage
DTC B2740 5a: Front Fog Lights Switch Stuck

### 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.

### Conditions for Running the DTC

• | Battery voltage must be between 9-16 volts.

• | Front fog lamps ON.

### Conditions for Setting the DTC

#### B2740 05

The DTC will set when the IPC detects a short to voltage or an open/high resistance in the front fog lamp switch signal circuit.

#### B2740 5a

The DTC will set when the IPC detects a short to ground in the front fog lamp switch signal circuit.

### Actions Taken When the DTC Sets

When DTC B2740 is present, the front fog lamps will not operate when the park lamps are ON and the front fog lamp switch is active.

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC no longer exists.

• | A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

### 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 Testing

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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Switch Replacement

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