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 Pedal Position Sensor 5-Volt Reference | C0277 06, C0870 03 | C0277 06 | 1 | --
Center High Mounted Stop Lamp (CHMSL) Relay B+ | 2 | 2 | -- | --
Brake Pedal Position Sensor Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09
Center High Mounted Stop Lamp (CHMSL) Relay Control | B3903 02 | B3903 05 | B3903 05 | --
Center High Mounted Stop Lamp (CHMSL) Control | 2 | 2 | 2 | --
Left Rear Stop/Turn Lamp Control | 1 | 1 | 1 | --
Right Rear Stop/Turn Lamp Control | 1 | 1 | 1 | --
Brake Pedal Position Sensor Low Reference | -- | C0277 07 | 1 | --
Center High Mounted Stop Lamp (CHMSL) Ground | -- | 2 | 1 | --
Left Rear Stop/Turn Lamp Ground | -- | 1 | 1 | --
Right Rear Stop/Turn Lamp Ground | -- | 1 | 1 | --
Center High Mounted Stop Lamp (CHMSL) Relay Ground | -- | 2 | -- | --
1. Stop Lamps Malfunction 2. Center High Mounted Stop Lamp (CHMSL) 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 voltage to the center high mounted stop lamp (CHMSL) relay coil. When the CHMSL relay receives voltage from the BCM, the relay coil is energized and the CHMSL relay switch contacts close applying battery voltage to the CHMSL, transmission control module (TCM), and engine control module (ECM).

### 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 Verification

1. Ignition ON, observe the scan tool Brake Lamp Cmd. parameter as you apply and unapply the brake pedal. The parameter should change between Off and On as the brake pedal is applied and released.

⇒ | If the parameter does not change as the brake pedal is applied and released, refer to Brake Pedal Position Sensor (BPPS) Malfunction.

2. With a scan tool, command the LR Stop/Turn Signal Lamp ON and OFF. The LR turn signal should turn ON and OFF when changing between the commanded states.

⇒ | If the LR stop lamp does not illuminate when commanded, refer to Stop Lamps Malfunction.

3. With a scan tool, command the RR Stop/Turn Signal Lamp ON and OFF. The RR turn signal should turn ON and OFF when changing between the commanded states.

⇒ | If the RR stop lamp does not illuminate when commanded, refer to Stop Lamps Malfunction.

### Circuit/System Testing

#### Stop Lamps Malfunction

1. Ignition OFF, disconnect the harness connector at the inoperative stop lamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground.

• | Stop/turn lamp ground terminal C - coupe

• | Stop/turn lamp ground terminal G - sedan

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

3. Connect a test lamp between the control circuit terminal A and ground.
4. Ignition ON, command the appropriate Stop/Turn Signal 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 tail lamp assembly.

#### Center High Mounted Stop Lamp (CHMSL) Malfunction

1. Ignition OFF, disconnect the CHMSL 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. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage.

4. Verify that a test lamp illuminates between the B+ circuit terminal 30 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 87 for a short to ground. If the circuit tests normal, test or replace the CHMSL relay.

5. Ignition OFF, disconnect the harness connector at the CHMSL.
6. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal B and ground.

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

7. Connect the harness connector at the CHMSL.
8. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the CHMSL is illuminated.

⇒ | If the CHMSL does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, replace the CHMSL.

9. Connect a test lamp between the control circuit terminal 85 and ground.
10. Ignition ON, command the stop lamps ON and OFF by applying and releasing the brake pedal. 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.

11. If all circuits test normal, test or replace the CHMSL.

#### Brake Pedal Position Sensor (BPPS) Malfunction

1. Ignition OFF, disconnect the harness connector at the BPPS.
2. Ignition ON, verify that a test lamp does not illuminate between the low reference circuit terminal C and ground.

⇒ | If the test lamp illuminates, test the low reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.

3. Ignition ON, test for 4.8 volts and 5.2 volts between the 5-volt reference circuit terminal A and ground.

⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.

4. If all circuits test normal, replace the BPPS.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Tail Lamp Replacement

• | High Mount Stop Lamp Replacement

• | Relay Replacement

• | Brake Pedal Position Sensor Replacement

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