Antilock Braking System (ABS)

WHEEL SPEED SENSOR OPERATION

As each wheel turns, the wheel speed sensor for that wheel creates a small AC voltage as a toothed sensor ring, mounted on the drive axle or hub/bearing assembly, is passed by the stationary sensor. The sensor consists of a permanent magnet and coil and generates voltage by magnetic induction. The frequency of the wheel speed sensor signal is proportional to wheel speed.

The EBCM uses the wheel speed sensor signal to calculate vehicle reference speeds and individual speed, acceleration and slip values for each wheel. These values are used to determine when anti-lock control is required.

WHEEL SPEED SENSOR CABLES

In order to prevent electromagnetic interference from disturbing the wheel speed sensor signal, the sensor cables are protected with grounded shielding (indicated by dashed lines in the above schematic). This shield surrounds the two individual sensor wires. A black conduit surrounds the wires and shield.

When servicing the sensor cables, the sensor wires are accessible by separating the shielding. If the shielding is disturbed, repair as required.

CODES 5-8: LOW WHEEL SPEED SENSOR OUTPUT

ABS diagnostic codes 5-8 will set in case of low output from a wheel speed sensor. Intermittent or continuous low output conditions which will cause codes 5-8 to set. If a low output condition is detected during a hard acceleration, codes 5-8 cannot set; codes 9 and 10 will set instead.

CODES 9 AND 10: DIAGONAL WHEEL SPEED SENSOR ERROR

Under conditions of hard acceleration, the EBCM cannot distinguish between specific wheel speed sensors in the event of a failure. It can, however, determine which diagonal circuit the failure occurred on. Code 9 will set if a failure is detected on the left front/right rear diagonal and Code 10 will set if a malfunction is noted on the right front/left rear diagonal. Codes 9 and 10 may also set with the compact spare installed.

If a Code 9 or 10 is set and a wheel speed sensor malfunction is present, the EBCM is able to determine which sensor has failed if the car is accelerated slowly. Code 9 or 10 will be replaced by the appropriate wheel speed sensor low output code (5-8).