With Variable Effort Steering (VES)

DTC 21: Left Front Wheel Speed = 0.:

DTC 21 Left Front Wheel Speed = 0 (For ABS With VES Only):

CIRCUIT DESCRIPTION
As a toothed ring passes by the wheel speed sensor, changes in the electromagnetic field cause the wheel speed sensor to produce a sinusoidal (AC) voltage signal whose frequency is proportional to wheel speed. The magnitude of this signal is directly related to wheel speed and the proximity of the wheel speed sensor to the toothed ring, often referred to as the air gap.

Diagnostic Trouble Code (DTC) WILL SET WHEN:
DTC 21 can be set when the vehicle is not in an Antilock Braking System (ABS) stop. A malfunction exists if the left front wheel speed=0 and the vehicle speed is greater than 8 km/h (5 mph).

ACTION TAKEN:
A malfunction DTC is stored, Antilock Braking System/Variable Effort Steering (ABS/VES) is disabled and the ABS warning lamp is turned "ON."

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Identifies if a wheel speed sensor or circuitry is damaged and visibly apparent.
2. Tests wheel speed sensor for proper resistance values.
3. Ensures the wheel speed sensor and toothed ring generate the proper voltage.
4. Ensures wheel speed sensor high and low circuits are not shorted together.
5. Ensures malfunction is not due to physical damage of the wheel speed sensor circuitry.

DIAGNOSTIC AIDS
An "Intermittent" malfunction is most likely caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.

The frequency of the malfunction can be checked by using the enhanced diagnostic function of the Tech 1.

If the customer's comments reflect that the ABS amber warning lamp is "ON" only during moist environmental changes, (rain, snow, vehicle wash) all wheel speed sensor circuitry should be thoroughly inspected for signs of water intrusion. Use the following procedure. Spray down the suspected area with 5% salt water solution (two teaspoons of salt to 12 oz. of water). Drive vehicle above 24 km/h (15 mph) for at least 30 seconds. If DTC returns immediately, replace suspected harness.

Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.

Resistance of the wheel speed sensor will increase with an increase in sensor temperature.

When replacing a wheel speed sensor, inspect the sensor terminals and harness connector for corrosion and/or water intrusion. If evidence of corrosion or water intrusion exists, replace wheel speed sensor harness.

If wheel speed sensor harness shows evidence of water intrusion, inspect wheel speed sensor for water intrusion. If water intrusion is evident, replace wheel speed sensor.