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 instrument panel cluster (IPC) monitors the brake fluid level switch via the brake fluid level sensor signal circuit. With the switch closed, the signal circuit is pulled to ground indicating low fluid level. When low fluid level is seen, the IPC will illuminate the red brake warning indicator. The body control module (BCM) monitors the park brake switch via the park brake switch signal circuit. With the park brake applied, the switch is closed and the signal circuit is grounded. The BCM will then send a serial data message to the IPC requesting the red brake warning indicator be illuminated.

### Reference Information

#### Schematic Reference

Hydraulic Brake Schematics

#### Connector End View Reference

Hydraulic Brake Connector End Views

#### Description and Operation

Brake Warning System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Verification

1. Verify the park brake is released and the brake fluid is at the proper level.

⇒ | If the brake fluid is not at the proper level, refer to Brake Fluid Loss .

2. Ignition ON, perform the scan tool IPC Display Test. The red brake warning indicator should illuminate.

⇒ | If the red brake warning indicator does not illuminate, replace the IPC.

3. Observe the scan tool BCM Park Brake Switch parameter while applying and releasing the park brake. The parameter should cycle between Applied and Release.

⇒ | If the parameter does not cycle between the specified values, refer to Park Brake Switch Circuit Malfunction.

4. Verify the scan tool EBCM Brake Fluid Level Sensor parameter is OK.

⇒ | If not the specified value, refer to Brake Fluid Level Switch Circuit Malfunction.

### Circuit/System Testing

#### Park Brake Switch Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the park brake switch.
2. Ignition ON, verify the scan tool BCM Park Brake Switch parameter is Released.

⇒ | If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the BCM.

3. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool BCM Park Brake Switch parameter is Applied.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance.

4. If all circuits test normal, test or replace the park brake switch.

#### Brake Fluid Level Switch Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the brake fluid level switch.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal A and ground.

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

3. Ignition ON, verify the scan tool EBCM Brake Fluid Level Sensor parameter is OK.

⇒ | If not the specified value, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the IPC.

4. Install a 3A fused jumper wire between the signal circuit terminal B and the ground circuit terminal A. Verify the scan tool EBCM Brake Fluid Level Sensor parameter is Low.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPC.

5. If all the circuits test normal, test or replace the brake fluid level 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 and IPC replacement, setup, and programming