For 1990-2009 cars

### 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 | Go to Symptoms - Hydraulic Brakes
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 |

1. Turn OFF the ignition.
2. Back-probe the Multi-function Alarm Module (MFAM) in order to connect a test lamp between the brake warning indicator supply voltage 2 circuit and a good ground. Refer to Probing Electrical Connectors in Wiring Systems.
3. Crank or start the engine.

Does the test lamp illuminate for 4 seconds and then turn OFF?

Go to Step 5

Go to Step 11

5 |

1. Remove the instrument panel cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages, and Console.
2. Inspect the auxiliary brake indicator lamp for an open filament.

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 |

1. Turn OFF the ignition.
2. Disconnect the Multi-Function Alarm Module harness connector.
3. Turn ON the ignition.
4. Test the generator turn on signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

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