DTC 21 - Left Front Wheel Speed Equals Zero Or Unreasonable: Notes

As a toothed ring passes the wheel speed sensor, changes in electromagnetic field cause sensor to produce an AC voltage signal. Frequency of signal is proportional to wheel speed. Magnitude of signal is directly related to wheel speed and the proximity of the wheel speed sensor to the toothed ring. This distance is also referred to as "air gap"

DTC can be set when vehicle is not in an ABS stop. If the sensors speed is less than one-half of the vehicle's referenced speed and the vehicle's referenced speed is greater than 5 MPH, a malfunction exists.

1. Verifies malfunction is currently present.
2. Identifies a wheel speed sensor or sensor circuit that is visibly damaged.
3. Checks wheel speed sensor for proper resistance.
4. Ensures wheel speed sensor and sensor ring generate the proper voltage.
5. Ensures wheel speed sensor is not shorted to ground.
6. Checks for proper voltages at speed sensor harness connector.
7. Ensures wheel speed sensor circuit is not internally shorted.
8. Checks for open in Blue wire.
9. Checks for open in Blue/Black wire
10. Checks for short to ground in both wheel speed signal circuits.
11. Ensures DTC was not set due to a poor connection.