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
--- | --- | --- | --- | ---
Brake Position Sensor Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09
Stop Lamp Switch Signal | B3903 02, P0572 | B3903 05, P0573 | B3903 05, P0573 | --
Brake Position Sensor 5-Volt Reference | C0870 03 | C0870 03 | C0870 07 | --
Brake Position Sensor Low Reference | -- | C0277 06 | C0277 07 | --
Left Rear Stop/Turn Lamp Supply Voltage | 1 | 1 | 1 | --
Right Rear Stop/Turn Lamp Supply Voltage | 1 | 1 | 1 | --
Center High Mounted Stop Lamp (CHMSL) Ground | -- | 2 | 2 | --
Left Rear Stop/Turn Lamp Ground | -- | 1 | 1 | --
Right Rear Stop/Turn Lamp Ground | -- | 1 | 1 | --
1. Stop Lamps Malfunction 2. High Mounted Stop Lamp Malfunction

### Circuit/System Description

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery positive voltage to the stop lamps, center high mounted stop lamp (CHMSL), transmission control module (TCM), and engine control module (ECM). The stop lamps will not operate unless the ignition is in the ON position. Ground for the left rear stop lamps is provided at G400. Ground for the right rear stop lamps is provided by G402.

### Diagnostic Aids

Important: The stop lamps will not illuminate unless the ignition is in the ON position. For more detailed information concerning stop lamp operation, refer to Exterior Lighting Systems Description and Operation.

### Reference Information

#### Schematic Reference

Exterior Lights Schematics

#### Connector End View Reference

Lighting Systems Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Output Controls

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Testing

#### Stop Lamps Malfunction

1. Ignition OFF, disconnect harness connector at the inoperative stop lamp.
2. Test for less than 1.0 ohm of resistance between the ground circuit and ground.

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

3. Connect a test lamp between the stop lamp supply voltage circuit and ground.
4. Command the inoperative stop lamp 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 voltage. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, replace the inoperative stop lamp.

#### High Mounted Stop Lamp Malfunction

1. Ignition OFF, disconnect the harness connector at the CHMSL.
2. Test for less than 1.0 ohm of resistance between the ground circuit terminal B and ground.

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

3. Connect a test lamp between the stop lamp switch signal circuit terminal A and ground circuit terminal B.
4. Ignition ON, apply the brake pedal ON and OFF. The test lamp should turn ON and OFF as the brake pedal is applied and released.

⇒ | If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, replace the CHMSL.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | High Mount Stop Lamp Replacement

• | Tail Lamp Replacement

• | Tail Lamp Bulb Replacement

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