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 |
|---|---|---|---|---|
B+, BCM C4 terminal 1 | 1 | 1 | -- | -- |
B+, BCM C4 terminal 3 | 3 | 3 | -- | -- |
Brake Position Sensor 5-Volt Reference | C0277 06, C0890 03 | C0277 06 | C0277 06 | -- |
Stop Lamp Switch Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09, C0277 4B |
CHMSL Supply Voltage | B3445 00, B3884 00 | 5 | 6 | -- |
Left Rear Stop/Turn Lamp Supply Voltage | 1 | 1 | 2 | -- |
Right Rear Stop/Turn Lamp Supply Voltage | 3 | 3 | 4 | -- |
Low Reference - Brake Position Sensor | -- | C0277 06 | -- | -- |
Ground - Center High Mounted Stop Lamp (CHMSL) | -- | 5 | -- | -- |
Ground - Left Rear Stop/Turn Lamp | -- | 1 | -- | -- |
Ground - Right Rear Stop/Turn Lamp | -- | 3 | -- | -- |
| ||||
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 both rear stop lamp/turn signals is provided by G302.
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
Connector End View Reference
Lighting Systems Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
- Ignition ON, observe the rear turn signals while commanding the left and right turn signals ON and OFF with a scan tool. The left and right rear turn signals should illuminate and flash when commanded ON.
- Observe the scan tool LR Turn Signal and RR Turn Signal parameters while applying the brake pedal. The parameter readings should be On while the brake pedal is applied.
- Observe the CHMSL as the brake pedal is applied and released. The CHMSL should turn ON and OFF as the brake pedal is applied and released.
| ⇒ | If the rear turn signals do not operate as specified, refer to Turn Signal Lamps and/or Indicators Malfunction . |
| ⇒ | If not the specified value, replace the BCM. |
| ⇒ | If the CHMSL does not turn ON and OFF as specified, refer to the Center High Mounted Stop Lamp Circuit Test. |
Circuit/System Testing
Center High Mounted Stop Lamp Circuit Test
- Ignition OFF, disconnect the harness connector at the CHMSL.
- Ignition OFF, test for less than 10.0 ohms between the appropriate ground circuit terminal listed below and ground.
- Connect a test lamp between the appropriate supply voltage circuit terminal listed below and the ground.
- Ignition ON, apply and release the brake pedal. The test lamp should turn ON and OFF as the brake pedal is applied and released.
- If all circuits test normal, replace the CHMSL.
| • | Sedan - terminal A |
| • | Coupe - terminal B |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| • | Sedan - terminal B |
| • | Coupe - terminal A |
| ⇒ | If the test lamp is always ON, test the supply voltage circuit for a short to voltage. If the circuit tests normal, replace the BCM. |
| ⇒ | If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
