DTC 21 Left Front Wheel Speed Is Zero Or Unreasonable: Notes

As tooth ring passes wheel speed sensor, changes in magnetic fields cause wheel speed sensor to produce an AC voltage signal whose frequency is proportional to wheel speed. The magnitude of the signal is directly related to wheel speed and proximity of wheel speed sensor to tooth ring, referred to as air gap. EBCM uses signal to compare individual wheel speed data and to detect wheel lock-up.

DTC 21 can set when vehicle is not in an ABS stop. If left front wheel speed is less than 1/2 of vehicle speed and vehicle speed is greater than 5 MPH a malfunction exists. DTC will be stored, ABS will be disabled and ABS warning light will turn on.

1. Checks for apparent physical damage that may cause DTC to set.
2. Checks if sensor resistance is correct.
3. Verifies sensor can generate appropriate output signal.
4. Ensures sensor circuitry is not shorted to ground.
5. Checks for proper voltage at sensor harness.
6. Ensures sensor circuitry is not shorted to ground.
7. Checks for open in wheel signal low circuit.
8. Checks for open in wheel signal high circuit.
9. Ensures DTC 21 was not set due to poor connection at EBCM or physical damage to circuitry.
10. Checks for short to battery voltage in either high or low wheel signal circuits.
11. Ensures short to battery voltage was not due to physical damage of circuitry.
12. Tests for short between wheel signal high and low circuits.
13. Ensures malfunction was not due to poor connection at wheel speed sensor or physical damage.