When the brake pedal is pressed during driving, the wheels can lock before the vehicle comes to a stop. In such an event, the maneuverability of the vehicle is reduced if the front wheels are locked, and the stability of the vehicle is reduced if the rear wheels are locked, creating an extremely unstable condition. The ABS precisely controls the slip rate of the wheels to ensure maximum grip force from the tires, thereby ensuring the maneuverability and stability of the vehicle. (Scheme 1)for views of ABS components.
The ABS calculates the slip rate of the wheels based on the vehicle speed and the wheel speed, then it controls the brake fluid pressure to reach the target slip rate. (Scheme 2)
Scheme 1
Scheme 2
| CAUTION | See ANTI-LOCK BRAKE SAFETY PRECAUTIONS article in GENERAL INFORMATION. |
Note. For more information on brake system, see DISC & DRUM article.
Pump Motor Operation Mode
When starting the pressure reducing mode, the pump motor is on. When stopping ABS operation, the pump motor is off. The reservoir fluid is pumped out by the pump, through the damping chamber, to the master cylinder.
Continuous Operation (Chipped Pulser)
- Clear the DTC.
- Test-drive the vehicle at 19 MPH (30 km/h) or more. Does the ABS indicator come on and is DTC 21 indicated? If yes, go to next step. If no, the system is okay at this time.
- Check the pulser gears for a chipped tooth. Are the pulser gears okay? If yes, check for loose terminals in the ABS control unit 31-pin connector. If necessary, substitute a known-good ABS modulator-control unit, and recheck. If no, replace the driveshaft or hub unit with the chipped pulser gear.