Code 21 - Right Front Wheel Speed Sensor Fault

Toothed wheel generates a voltage pulse as it moves past sensor. EBCM uses these pulses to determine wheel speed. Amount of voltage generated in each pulse depends on wheel speed and air gap between sensor and toothed wheel.

EBCM uses 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 needed.

EBCM performs 2 basic types of checks on wheel speed sensors: sensor continuity and sensor output.

Code 21 will set if open or short exists in circuit No. 872, open exists in circuit No. 833 or an open exists across sensor coil.

Code 21 will also set if EBCM detects low output from wheel speed sensor. Conditions include shorted sensor coil and/or improperly installed wheel speed sensor.

1. Checks for correct resistance reading of wheel sensor.
2. Checks for short to ground in right front wheel speed sensor.
3. Checks for short between right front wheel sensor wires.
4. Checks for short to voltage in circuits No. 833 and 872.
5. Checks for short to ground in circuits No. 833 and 872.
6. Checks for open circuit or high resistance in circuits No. 833 and 872.
7. Checks for intermittent in right front wheel sensor circuit. If intermittent is not found, wheel sensor may be faulty. Replace wheel sensor, and road test vehicle. If code returns, replace EBCM and road test vehicle.