Once the light has turned on, there will be at least one diagnostic fault code stored in the ABS Computer. That will lead you to the circuit or system with the problem, not necessarily the specific defective part. The buzzing you're hearing is the computer activating the solenoids to modulate brake fluid pressure to one or more wheels in response to the computer thinking one wheel is slowing down too fast. That can be due to a loss of signal from one wheel speed sensor for a number of reasons. When the yellow warning light turns on is a clue too. If it comes on while driving and not pressing the brake pedal, the computer might be detecting an extra pulse from one front wheel speed sensor per tire revolution due to a cracked tone ring. That's what's happening on my '95 Grand Caravan. It takes from 100 feet to a mile or more before the light turns on, and it will reset off each time the engine is restarted. If your light turns on before the van is moving, there is more likely a problem in the hydraulic controller or pump. The system is deactivated when the light is on.
I also have a '93 Dynasty with the Bendix-10 system. That one gets its power assist from the pressurized brake fluid that is held in storage. If you have that system, a pump problem will have an affect on your power assist. There was a recall on that system to replace the piston assembly in the master cylinder. My '95 ABS system is different. That uses a standard vacuum power assist booster so it will still have normal power assist if the ABS system shuts down. I'm not sure which system was used in '94.
Start by finding a mechanic with a scanner that can access the ABS computer to read the fault code(s).
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Thursday, November 25th, 2010 AT 7:00 PM