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 | C0277 06, C0890 03 | C0277 06 | C0277 06 | -- |
Stop Lamp Switch Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09, C0277 4B |
Brake Position Sensor Low Reference | -- | C0277 06 | -- | -- |
CHMSL Control | B3445 00 | 5 | 6 | -- |
Left Stop Lamp Control | 1 | 1 | 2 | -- |
Right Stop Lamp Control | 3 | 3 | 4 | -- |
Center High Mounted Stop Lamp (CHMSL) Ground | -- | 5 | -- | -- |
Left Rear Stop/Turn Lamp Ground | -- | 1 | -- | -- |
Right Rear Stop/Turn Lamp Ground | -- | 3 | -- | -- |
1. Left Stop/Turn Lamp Inoperative 2. Left Stop/Turn Lamp Always On 3. Right Stop/Turn Lamp Inoperative 4. Right Stop/Turn Lamp Always On 5. Center High Mounted Stop Lamp (CHMSL) Inoperative 6. Center High Mounted Stop Lamp (CHMSL) Always On | ||||
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 B+ 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.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, observe the CHMSL while pressing and releasing the brake pedal. The CHMSL should turn ON and OFF.
- Ignition ON, observe the rear stop lamps while pressing and releasing the brake pedal. The stop lamps should turn ON and OFF.
| ⇒ | If the CHMSL does not turn ON and OFF, refer to High Mounted Stop Lamp Circuit Test. |
| ⇒ | If the stop lamps do not turn ON and OFF, refer to Stop Lamps Circuit Test. |
Circuit/System Testing
High Mounted Stop Lamp Circuit Test
- Ignition OFF, disconnect the harness connector at the CHMSL.
- Ignition OFF, test for less than 5.0 ohms between the ground circuit terminal listed below and ground.
- Connect a test lamp between the control 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.
| • | RPO W49 - Terminal A |
| • | RPO WDA/Z88 - Terminal 1 |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| • | RPO W49 - Terminal B |
| • | RPO WDA/Z88 - Terminal 2 |
| ⇒ | 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. |
Stop Lamps Circuit Test
- Ignition OFF, disconnect the harness connector at the brake pedal position sensor.
- Verify that a test lamp illuminates between the low reference circuit terminal C and B+.
- Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal A and ground.
- Ignition OFF, disconnect harness connector at the inoperative stop/turn lamp assembly.
- Ignition OFF, test for less than 5.0 ohms between the ground circuit listed below and ground:
- Connect a test lamp between the control circuit listed below and ground:
- Ignition ON, command the appropriate LR or RR Turn Signal ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, replace the inoperative stop/turn signal lamp assembly.
| ⇒ | If the test lamp does not illuminate, test the low reference circuit for 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. |
| ⇒ | 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. |
| • | RPO Z88 - terminal D |
| • | All others - terminal B |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| • | RPO Z88 - terminal E |
| • | All others - terminal A |
| ⇒ | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
