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 | 2, 6 | 2, 6 | -- | -- |
B+, BCM C4 Terminal 3 | 3, 7 | 3, 7 | -- | -- |
B+, BCM C4 Terminal 4 | 4 | 4 | -- | -- |
Brake Apply Sensor Supply Voltage | C0870 03 | C0870 03 | C0870 07 | -- |
Brake Apply Sensor Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09 |
Brake Pedal Position Sensor Low Reference | -- | 1, 5 | -- | -- |
Stop Lamp Switch Signal | C0297 00 | -- | -- | -- |
CHMSL Supply Voltage | B3445 00 | 4 | 4 | -- |
Stop Lamp Relay B+ -- Export | 5 | 5 | -- | -- |
Stop Lamp Relay/CHMSL Supply Voltage -- Export | B3445 00 | 5 | 5 | -- |
Left Rear Stop/Turn Lamp Supply Voltage | 2 | 2 | 2 | -- |
Right Rear Stop/Turn Lamp Supply Voltage | 3 | 3 | 3 | -- |
Left Rear Stop Lamp Supply Voltage -- Export | 6 | 6 | 6 | -- |
Right Rear Stop Lamp Supply Voltage -- Export | 7 | 7 | 7 | -- |
Center High Mounted Stop Lamp (CHMSL) Ground | -- | 4 | -- | -- |
Left Rear Tail Lamp Assembly Ground | -- | 2, 6 | -- | -- |
Right Rear Tail Lamp Assembly Ground | -- | 3, 7 | -- | -- |
Stop Lamp Relay Ground -- Export | -- | 5 | -- | -- |
| ||||
Circuit/System Description
Domestic
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). Ground for the left tail lamp assembly and CHMSL is provided by G402 and ground for the right tail lamp assembly is provided by G403.
Export
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 stop lamp relay coil control circuit, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL). When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage from the STOP LAMPS EXP Fuse to illuminate the rear stop lamps and trailer stop lamps. Ground for the left tail lamp assembly and CHMSL is provided by G402 and ground for the right tail lamp assembly is provided by G403.
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 Testing
Stop Lamps Circuit Test -- Domestic
- Ignition OFF, disconnect the (C4) harness connector at the BCM.
- Ignition ON, verify a test lamp illuminates between the terminals listed below and ground.
- 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 OFF, disconnect harness connector at the inoperative stop/turn lamp.
- Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal C and ground.
- Connect a test lamp between the supply voltage circuit terminal B 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 bulb or lamp assembly.
| • | B+ terminal 1 |
| • | B+ terminal 3 |
| • | B+ terminal 4 |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the circuit fuse is open, test the B+ circuit and the respective stop lamp circuits for a short to ground. |
| ⇒ | 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 ground circuit for an open/high resistance. |
| ⇒ | 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. |
Stop Lamps Circuit Test -- Export
- Ignition OFF, disconnect the (C4) harness connector at the BCM.
- Ignition ON, verify a test lamp illuminates between the B+ terminals listed below and ground.
- 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 OFF, disconnect the STOP LAMP EXP Relay from the rear fuse block.
- Test for less than 5 ohms of resistance between the ground circuit terminal 9 and ground
- Ignition ON, verify a test lamp does not illuminate between the supply voltage terminal 6 and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal 10 and ground.
- Connect a test lamp between the supply voltage circuit terminal 8 and the ground circuit terminal 9.
- Ignition ON, apply and release the brake pedal. The test lamp should turn ON and OFF as the brake pedal is applied and released.
- Disconnect the harness connector at the inoperative stop lamp.
- Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal H and ground.
- Connect a test lamp between the supply voltage circuit terminal B and ground.
- Connect a 3A fused jumper wire between the stop lamp relay B+ circuit terminal 10 and the supply voltage circuit terminal 6. The test lamp should illuminate.
- If all circuits test normal, test or replace the stop lamp relay.
| • | B+ terminal 1 |
| • | B+ terminal 3 |
| • | B+ terminal 4 |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the circuit fuse is open, test the B+ circuit and the respective stop lamp circuits for a short to ground. |
| ⇒ | 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 ground circuit for an open/high resistance. |
| ⇒ | If the test lamp illuminates, test the supply voltage circuit for a short to voltage. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
| ⇒ | 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. |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If the test lamp does not illuminate, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the bulb. |
High Mounted Stop Lamp Malfunction
- Ignition OFF, disconnect the harness connector at the CHMSL.
- Ignition OFF, test for less than 5.0 ohm of resistance between the ground circuit terminal B and ground.
- Connect a test lamp between the supply voltage circuit terminal A and the ground circuit terminal B.
- 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.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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. |
Component Test
Relay Test
- Ignition OFF, disconnect the relay.
- Test for 70-100 ohms of resistance between terminals 85 and 86.
- Test for infinite resistance between the following terminals:
- Install a 10A fused jumper wire between relay terminal 85 and B+. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.
| ⇒ | If the resistance is not within the specified range, replace the relay. |
| • | 30 and 85 |
| • | 30 and 86 |
| • | 30 and 87 |
| • | 85 and 87 |
| ⇒ | If not the specified value, replace the relay. |
| ⇒ | If greater than the specified range, replace the relay. |
Repair Instructions
Important: Perform the Brake Pedal Position Sensor Calibration after replacement of the brake pedal position sensor.
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
