C1234

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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 small 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.

CONDITIONS FOR SETTING THE DTC
DTC C1234 can be set anytime after the Electronic Brake Control Relay has been turned ON. If the EBCM detects an out of range voltage in either the high or low wheel speed circuits, a malfunction exists.

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

CONDITIONS FOR CLEARING THE DTC
Conditions for the malfunction are no longer present and the scan tool CLEAR DTCs function is used. One hundred ignition switch key cycles have passed with no malfunctions detected.

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 scan tool.

If the customer's comments reflect that the ABS indicator lamp is ON only during humid conditions (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 Percent salt water solution (two teaspoons of salt to 12 ounces of water). Drive vehicle above 24 km/h (15 mph) for at least 30 seconds. If the DTC returns immediately, replace suspected harness.

Any circuitry that is suspected of 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 measuring for a short to ground in a wheel speed sensor wiring circuit, manually switch the DMM to the Meg-Ohms range. This will ensure a high resistance short to ground can be found.

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 the 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 the wheel speed sensor.