Anti-Lock Brake System - BOSCH Abs-3: Operation
Each wheel sensor sends an AC electrical signal to the ABCM. The ABCM translates this information as wheel speed. When any decelerating wheel speed rate is determined to be excessive in comparison to other speed sensored wheels, the ABCM cycles hydraulic brake pressure to each wheel to equalize speed of all wheels. Refer to Fig. Fig 2 . ABS turns itself off at 3-5 MPH. Minor lock-up may occur at this point.
Red BRAKE warning light will come on when ignition switch is in START position. Light should go off when ignition is released. If not, light indicates the following problems: parking brake not fully released, low brake fluid, low accumulator pressure or low hydraulic pressure.
Amber ANTI-LOCK warning light will come on for 1-30 seconds after ignition is turned on. This indicates system is performing a self-diagnostic test. If light does not go off after indicated time, system has found a fault. ABS is deactivated during this period. Normal braking is unaffected. Testing should be done to find and correct fault. See DIAGNOSIS & TESTING in this article.