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
--- | --- | --- | --- | ---
5-Volt Reference | C0277 06 | C0277 06 | C0277 07 | --
Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09
Low Reference | -- | 1 | -- | --
Brake Lamps | B3445 02 | B3445 04 | B3445 01 | --
Right Brake Lamp | B3878 02 | B3878 04 | B3878 01 | --
1. Stop Lamps Malfunction

### Circuit/System Description

The brake pedal position (BPP) sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position (BPP) 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 V reference voltage to the brake pedal position (BPP) 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 control circuit and center high mounted stop lamp control circuit. When the control circuit is energized the stop lamps are illuminated.

#### 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 Verification

• | Ignition ON, observe the scan tool Brake Switch parameter. The reading should be between Inactive/Active and change when the brake pedal is pushed or released.

• | Ignition ON, perform the Brake Lamp Command test. The brake lamps should be ON / OFF.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the B22 Brake Pedal Position (BPP) Sensor.
2. Ignition OFF, test for less than 5 Ω between the low reference circuit terminal C and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module (BCM).

3. Ignition ON, command the Brake Lamp Command test with a scan tool. The brake lamps should turn ON and OFF when changing between the commanded states.

⇒ | If the brake lamps did not turn ON and OFF replace the K9 Body Control Module (BCM).

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM replacement, setup and programming