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 5-Volt Reference | C0870 03 | C0870 03 | C0870 07 | --
Brake Position Sensor Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09
Stop Lamp Relay Control | B3903 02 | B3903 05 | B3903 05 | --
Left Rear Tail/Stop Lamp Control | 1 | 1 | 1 | --
Right Rear Tail/Stop Lamp Control | 1 | 1 | 1 | --
Brake Position Sensor Low Reference | -- | C0277 06 | C0277 07 | --
Center High Mounted Stop Lamp (CHMSL) Ground | -- | 2 | -- | --
Left Rear Tail/Stop Lamp Ground | -- | 1 | -- | --
Right Rear Tail/Stop Lamp Ground | -- | 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 voltage to the stop lamp relay control circuit. This energizes the stop lamp relay coil causing the relay switch contacts to close. With the relay switch contacts closed, battery voltage flows from the STOP LAMP fuse through the relay switch contacts to the rear stop lamps, center high mounted stop lamp (CHMSL), 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. Ground for the coil side of the stop lamp relay is provided at G102.

### Reference Information

#### Schematic Reference

Exterior 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 stop lamp relay.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 86 and ground.

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

3. Verify that a test lamp illuminates between the B+ circuit terminal 87 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+ circuit fuse is open, test the control circuit terminal 30 for a short to ground. If the circuit test normal, test or replace the stop lamp relay.

4. Disconnect the harness connector at the Inoperative stop lamp.
5. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal G and ground.

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

6. Connect the harness connector at the inoperative stop lamp.
7. Connect a 15 A fused jumper wire between the B+ circuit terminal 87 and the control circuit terminal 30. Verify the stop lamps illuminate.

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

8. Connect a test lamp between the control circuit terminal 85 and the ground circuit terminal 86.
9. Ignition ON, command the stop lamps ON and OFF by applying and releasing the brake pedal. 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 control 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 control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | High Mount Stop Lamp Replacement

• | Tail Lamp Replacement

• | Relay Replacement

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