I would be looking at the check valve being jammed up first ?
Both models are equipped with a dual-diaphragm vacuum booster. The power brake booster is a dual diaphragm, vacuum assisted power brake booster. The booster reduces brake pedal pressure and travel distance. The booster is located on the left side of the bulkhead in the engine compartment, between the brake pedal and brake master cylinder. The booster is divided into separate chambers by the diaphragm and will not operate if vacuum is restricted or if any of the vacuum related power brake components fail. The brake booster is replaced as an assembly. If the power assist fails, the brake system will continue to operate with increased brake pedal effort. See Fig. 4 .
The power brake booster check valve is located on the front of the power brake booster. The check valve is positioned between the power brake booster and the power brake booster hose. It closes when the engine is turned off. In the closed position, it traps engine vacuum in the power brake booster and retains vacuum to provide several power assisted brake applications with the engine off.
PRINCIPLES OF OPERATION
The ABS control module receives wheel speed readings from both front wheel speed sensors and the rear differential speed sensor, and processes this information to determine if an ABS event is necessary. The wheel speed sensor electrically senses each tooth of the ABS sensor indicators as it passes through the wheel speed sensor's magnetic field.
The ABS control module continuously monitors and compares the rotational speed of each wheel speed sensor indicator and, when it detects an impending wheel lock, modulates brake pressure to the appropriate brake caliper(s). This is accomplished by triggering the Hydraulic Control Unit (HCU) to open and close the appropriate solenoid valves. Once the affected wheel returns to normal speed, the ABS control module returns the solenoid valves to their normal position, and normal (base) braking resumes.
The ABS control module is self-monitoring. When the ignition switch is turned to the RUN position, the ABS control module will do a preliminary electrical check, and at approximately 20 km/h (12 MPH), the pump motor is turned on for approximately one-half second. Any malfunction of the ABS system will cause the ABS to shut off; normal power assisted braking, however, remains.
Thursday, January 1st, 2009 AT 5:36 AM