Monday, November 21, 2011
2001 Chevrolet C-Series Medium Duty Truck B7 Auxiliary Brake Warning Indicator Always On
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. Test Description The numbers below refer to the step numbers on the diagnostic table. 3. This step tests if the multifunction alarm module is supplying voltage to the brake warning indicator supply voltage 2 circuit. 5. This step tests for a 12 volt signal from the MFAM. 7. This step tests if the MFAM is capable of supplying ground to the brake booster fluid flow switch signal circuit. Schematic Reference: Brake Warning System Schematics Did you review the Hydraulic Brake System Description and Operation and perform the necessary inspections? 1 Crank or start the engine while observing the AUX BRAKE indicator. 2 Does the AUX BRAKE indicator illuminate for 4 seconds and then turn OFF and remain OFF? 1. Turn OFF the ignition. 2. Disconnect the MFAM harness connector. 3. Turn ON the ignition. 3 Does the AUX indicator illuminate? 4 1. Turn OFF the ignition. 2. Reconnect the MFAM harness connector. 3. Apply the brake. Does the power brake booster pump motor run when the brake is applied? 5 1. Disconnect the harness connector of the power brake booster pump motor relay, which is located in the Maxi- Fuse center. 2. Connect a test lamp between the brake switch signal circuit and a good ground. 3. Crank or start the engine. Does the test lamp illuminate for 4 seconds and then turn OFF?
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