Circuit Description
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.
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 Auxiliary Brake indicator. Does the Auxiliary Brake indicator illuminate for 4 seconds and then turn OFF? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
3 | Are the Primary Brake and the Low Coolant indicators also inoperative at bulb check? | Go to Step 7 | Go to Step 4 |
4 |
Does the test lamp illuminate for 4 seconds and then turn OFF? | Go to Step 5 | Go to Step 11 |
5 |
Did you find and correct the condition? | Go to Step 13 | Go to Step 6 |
6 | Test the brake warning indicator supply voltage 2 circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
7 |
Did you find and correct the condition? | Go to Step 13 | Go to Step 8 |
8 | Test the neutral safety switch signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
9 | Inspect for poor connections at the instrument panel cluster 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 13 | Go to Step 10 |
10 | Replace the instrument panel cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages, and Console. Did you complete the replacement? | Go to Step 13 | -- |
11 | 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 13 | Go to Step 12 |
12 | Replace the MFAM. Refer to Multifunction Alarm Module Replacement in Instrument Panel, Gages, and Console. Did you complete the replacement? | Go to Step 13 | -- |
13 | Crank or start the engine while observing the Auxiliary Brake indicator. Does the Auxiliary Brake indicator illuminate for 4 seconds and then turn OFF? | System OK | Go to Step 3 |
