Anti-Lock Brake System With Traction Control System And VSES - BOSCH 5: Operation

During normal driving and braking operations, ABS acts like a conventional braking system. Wheel speed sensors transmit a small AC voltage signal about wheel acceleration, deceleration and slip value to EBCM. The EBCM controls braking by activating and deactivating BPMV.

The modulator valve assembly consists of rapidly switching solenoid valves, accumulator chamber and a return pump. The valves increase and decrease brake fluid pressure to each wheel to prevent wheel lock-up.

The modulator valve can supply only as much fluid pressure as applied through the master cylinder. The modulator valve alone cannot apply the brakes. A slight pulsation should be felt through brake pedal when ABS is active.

BRAKE warning indicator (Red) will illuminate when ignition switch is turned to START position, and should go out when ignition switch is turned to ON position. ANTI-LOCK indicator (Amber) and TRACTION CONTROL indicator (Amber) illuminate when ignition is turned on, and should go out after about 2 seconds. If any indicator remains illuminated more than 30 seconds after vehicle is started, system malfunction is indicated. See DIAGNOSIS & TESTING  .

Red BRAKE warning indicator will activate if parking brake is applied or brake fluid is low. Amber ANTI-LOCK indicator is controlled by EBCM and comes on if problem is detected with ABS. When indicator is illuminated, ABS is disabled and braking is accomplished by conventional brake system. If both warning indicators are illuminated, check conventional brake system for hydraulic system failure. Amber TRACTION CONTROL indicator is controlled by EBCM, and comes on if problem is detected with TCS. When indicator is illuminated, TCS is disabled and braking (conventional and ABS) is unaffected.