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.