The auxiliary brake system provides hydraulic fluid flow within the brake booster if the engine is OFF and the brake is applied. The system consists of the following 3 basic components:
• | The power brake booster pump motor relay |
• | The power brake booster fluid flow switch |
• | The power brake booster pump motor |
The multifunction alarm module (MFAM) performs a 4 second bulb check on the AUX BRAKE indicator immediately after the engine is cranked or started. The MFAM illuminates the indicator by supplying voltage to the lamp. During the bulb check, the MFAM also performs a diagnostic which tests the power brake booster pump motor relay, the power brake booster fluid flow switch and the power brake booster pump circuitry for electrical faults. The AUX BRAKE indicator remains illuminated if the MFAM detects an electrical fault in the system. The MFAM also sounds an audible warning when the AUX BRAKE indicator illuminates.
The numbers below refer to the step numbers on the diagnostic table.
This step tests if the multifunction alarm module is supplying voltage to the brake warning indicator supply voltage 2 circuit.
This step tests for a 12 volt signal from the MFAM.
This step tests if the MFAM is capable of supplying ground to the brake booster fluid flow switch signal circuit.
Step | Action | Yes | No |
---|---|---|---|
Schematic Reference: Brake Warning System Schematics | |||
1 | Did you review the Hydraulic Brake System Description and Operation and perform the necessary inspections? | Go to Step 2 | |
2 | Crank or start the engine while observing the AUX BRAKE indicator. Does the AUX BRAKE indicator illuminate for 4 seconds and then turn OFF and remain OFF? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
Does the AUX indicator illuminate? | Go to Step 14 | Go to Step 4 | |
4 |
Does the power brake booster pump motor run when the brake is applied? | Go to Step 5 | |
Does the test lamp illuminate for 4 seconds and then turn OFF? | Go to Step 7 | Go to Step 6 | |
6 |
Did you find and correct the condition? | Go to Step 18 | Go to Step 16 |
Does the test lamp illuminate for 4 seconds and then turn OFF? | Go to Step 9 | Go to Step 8 | |
8 | Test the brake booster fluid flow switch signal circuit for an open between the power brake booster pump motor relay and the MFAM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 18 | Go to Step 16 |
9 |
Does the test lamp illuminate for 4 seconds and then turn OFF? | Go to Step 11 | Go to Step 10 |
10 | Repair the open in the brake booster pump motor voltage supply circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 18 | -- |
11 | Use a DMM in order to test the circuit breaker, removed in step 8, for continuity. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | Go to Step 18 | Go to Step 12 |
12 |
Does the test lamp illuminate for 4 seconds and then turn OFF? | Go to Step 16 | Go to Step 13 |
13 | Repair the open or short to ground in the brake booster pump motor voltage supply circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 18 | -- |
14 |
Did you find and correct the condition? | Go to Step 18 | Go to Step 15 |
15 | Replace the instrument panel cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages, and Console. Did you complete the replacement? | Go to Step 18 | -- |
16 | Inspect for poor connections at the MFAM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 18 | Go to Step 17 |
17 | Replace the MFAM. Refer to Multifunction Alarm Module Replacement in Instrument Panel, Gages, and Console. Did you complete the replacement? | Go to Step 18 | -- |
18 | Crank or start the engine while observing the AUX BRAKE indicator. Does the AUX BRAKE indicator illuminate for 4 seconds and then turn OFF and remain OFF? | System OK | Go to Step 2 |