Code 21 - Right Front Wheel Speed Sensor: Notes

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

SERVICE ABS and SERVICE ASR indicators will be on and Code 21 will be set if speed sensor is faulty or if there is a short to voltage or ground in circuit No. 872 or circuit No. 833. Code will only set with ignition on and vehicle moving.

1. Checks for correct resistance reading of wheel speed sensor.
2. Checks for short to battery voltage in wheel speed sensor circuit wires.
3. Checks for short between wheel speed sensor circuit wires.
4. Checks for short to ground in circuit No. 872. Ground may be a hard, constant short to ground or a partial (resistive) short. A resistive short of less than 2 megohms can set a Code 21.
5. Checks if code resets during road test. If code is reset during road test, intermittent problems should be suspected.
6. Checks for intermittents in wiring and connectors.
7. Replace wheel bearing/speed sensor since it is the most likely cause of a code reset during road test. If code resets after sensor replacement, EBCM is detecting a fault in a speed sensor circuit when one does not exist.