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.

### Circuit/System Description

The body control module (BCM) monitors the park brake switch signal circuit and the brake fluid level sensor signal circuit, and sends the switch information to the IPC via the serial data bus. The instrument panel cluster (IPC) monitors the serial data bus, and illuminates the brake warning indicator if it is requested.

### Reference Information

#### Schematic Reference

Hydraulic Brake Schematics

#### Connector End View Reference

Component Connector End Views

#### 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. Verify that the brake warning indicator illuminates during the IPC bulb check.

⇒ | If the brake warning indicator does not illuminate during the bulb check, replace the IPC.

2. Observe the driver information center (DIC). Verify that the BRAKE FLUID message is not displayed.

⇒ | If the BRAKE FLUID message is displayed, then refer to Circuit/System Testing: BRAKE FLUID Message and Brake Warning Indicator Always On.

3. Apply the parking brake. Verify that the brake warning indicator illuminates.

⇒ | If the brake warning indicator does not illuminate, then refer to Circuit/System Testing: Brake Warning Indicator Inoperative when Park Brake is Applied.

4. Release the parking brake. Verify that the brake warning indicator turns off.

⇒ | If the brake warning indicator does not turn off, then refer to Circuit/System Testing: Brake Warning Indicator Always On.

5. Remove all of the brake fluid from the master cylinder reservoir. Wait 30 seconds. Verify that the brake warning indicator illuminates on the IPC.

⇒ | If the brake warning indicator does not illuminate, then refer to Circuit/System Testing: Brake Warning Indicator Inoperative when Brake Fluid is Low.

### Circuit/System Testing

#### BRAKE FLUID Message and Brake Warning Indicator Always On

1. Inspect the master cylinder reservoir for the proper brake fluid level.

⇒ | If brake fluid level is low, refer to Hydraulic Brake System Diagnosis.

2. Ignition ON. With the scan tool, select Instrument Panel Cluster, Special Functions, Display Test. Command the instrument panel indicators OFF. Verify that the brake warning indicator turns OFF, and then exit the Display Test.

⇒ | If the brake warning indicator does not turn OFF, replace the IPC.

3. Disconnect the brake fluid level switch connector. Wait 30 seconds. With a scan tool, observe the Brake Fluid Level Sensor parameter in the Body Control Module, Chassis data display. Verify that the scan tool Brake Fluid Level Sensor parameter remains Low.

⇒ | If the scan tool Brake Fluid Level Sensor parameter is OK, replace the brake fluid level switch.

4. Test the brake fluid level sensor signal circuit for a short to ground. Verify that the brake fluid level sensor signal circuit is not shorted to ground.

⇒ | If the brake fluid level sensor signal circuit is shorted to ground, repair the circuit.

5. Replace the BCM.

#### Brake Warning Indicator Always On

1. Ignition ON. With the scan tool, select Instrument Panel Cluster, Special Functions, Display Test. Command the instrument panel indicators OFF. Verify that the brake warning indicator turns OFF, and then exit the Display Test.

⇒ | If the brake warning indicator does not turn OFF, replace the IPC.

2. Disconnect the park brake switch connector. With a scan tool, observe the Park Brake Switch parameter in the Body Control Module, Lighting data display. Verify that the scan tool Park Brake Switch parameter is Active.

⇒ | If the scan tool Park Brake Switch parameter is Inactive, replace the park brake switch.

3. Test the park brake switch signal circuit for a short to ground. Verify that the park brake switch signal circuit is not shorted to ground.

⇒ | If the park brake switch signal circuit is shorted to ground, repair the circuit.

4. Replace the BCM.

#### Brake Warning Indicator Inoperative when Brake Fluid is Low

1. Ignition ON. With the scan tool, select Instrument Panel Cluster, Special Functions, Display Test. Command the instrument panel indicators ON. Verify that the brake warning indicator turns ON, and then exit the Display Test.

⇒ | If the brake warning indicator does not turn ON, replace the IPC.

2. Disconnect the brake fluid level switch. Connect a 3 amp fused jumper wire between the signal circuit terminal A and the ground circuit terminal B of the brake fluid level switch. Ignition ON, wait 30 seconds. Verify that the brake warning indicator remains OFF.

⇒ | If the brake warning indicator turns ON, replace the brake fluid level switch.

3. Test the signal circuit and the ground circuit for continuity. Verify that the signal circuit and the ground circuit does not have a high resistance or an open.

⇒ | If a high resistance or an open is found, repair the circuit.

4. Replace the BCM.

#### Brake Warning Indicator Inoperative when Park Brake is Applied

1. Ignition ON. With the scan tool, select Instrument Panel Cluster, Special Functions, Display Test. Command the instrument panel indicators ON. Verify that the brake warning indicator turns ON, and then exit the Display Test.

⇒ | If the brake warning indicator does not turn ON, replace the IPC.

2. Disconnect the park brake switch. Connect a 3 amp fused jumper wire between the signal circuit terminal A of the park brake switch and ground. Ignition ON, Verify that the brake warning indicator is OFF.

⇒ | If the brake warning indicator turns ON, replace the park brake switch.

3. Test the signal circuit for continuity. Verify that the signal circuit does not have a high resistance or an open.

⇒ | If a high resistance or an open is found, repair the circuit.

4. Replace the BCM.

### Component Testing

#### Brake Fluid Level Switch

1. Inspect the master cylinder reservoir for the proper brake fluid level.

⇒ | If brake fluid level is low, refer to Hydraulic Brake System Diagnosis.

2. Ignition OFF. Disconnect the brake fluid level switch connector. Measure the resistance between terminal A and terminal B of the brake fluid level switch. Verify that the resistance is greater than 75 k/Ohm.

⇒ | If there is less than 75 k/Ohm between terminal A and terminal B of the brake fluid level switch when the master cylinder reservoir is full, replace the brake fluid level indicator switch.

3. Remove all of the brake fluid from the master cylinder reservoir. Measure the resistance between terminal A and terminal B of the brake fluid level switch. Verify that the resistance is less than 25 Ω.

⇒ | If there is greater than 25 Ω between terminal A and terminal B of the brake fluid level switch when the master cylinder reservoir is empty, replace the brake fluid level indicator switch.

#### Park Brake Switch

1. Ignition OFF. Release the park brake. Disconnect the park brake switch connector. Verify that continuity does not exist between terminal A of the park brake switch and ground.

⇒ | If there is continuity between terminal A of the park brake switch and ground when the park brake is released, replace the parking brake indicator switch.

2. Apply the park brake. Verify that continuity exists between terminal A of the park brake switch and ground.

⇒ | If there is no continuity between terminal A of the park brake switch and ground when the park brake is applied, replace the parking brake indicator switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Brake Fluid Level Indicator Switch Replacement

• | Parking Brake Indicator Switch Replacement

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