A024

Diagnostic Chart:

Wiring Diagram:

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.

FAILURE CONDITION
DTC A024 can be set when the vehicle is not in an ABS stop. If the right rear wheel speed = 0 and the vehicle's reference speed is greater than 8 km/h (5 mph), a malfunction exists.

ACTION TAKEN
A malfunction DTC is stored, ABS is disabled and the ABS indicator lamp is turned "ON".

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test determines if DTC A035 is present.
2. This test verifies whether the malfunction is currently present.
3. This step is designed to identify a wheel speed sensor or circuitry that is damaged and visibly apparent.
4. This test checks to see that the wheel speed sensor is within proper resistance values.
5. This step verifies that the wheel speed sensor can generate an appropriate output signal.
6. This test checks for proper output voltage from the Electronic Brake Control Module (EBCM).
7. This checks for an open in the wheel signal low circuit.
8. This step insures that DTC A024 was not set due to a poor connection between the 24-way EBCM connector and the EBCM.
9. This test insures that wheel speed sensor circuitry is not internally shorted.
10. This checks for an open in the wheel signal high circuit.

DIAGNOSTIC AIDS
An "Intermittent" malfunction may be 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 customers comments reflect that the ABS indicator 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. If DTC is not current, clear DTCs and simulate the effects of water intrusion. Use the following procedure. Spray down the suspected area with a 5% salt water solution (two teaspoons of salt to 12 oz. of water). Start vehicle, allow vehicle to run for 10 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.

When measuring wheel speed sensor resistance, insure vehicle is at room temperature. Wheel speed sensor resistance will vary with 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.