C0040

DTC C0040

Circuit Description

As the front wheels spin, each wheel speed sensor produces a digital square wave signal. The electronic brake control module (EBCM) uses the frequency of the wheel speed sensor signal to determine wheel speed.

Conditions for Running the DTC

Both of the conditions listed below may be required to set the DTC.

- The ignition is ON.
- The vehicles achieves a speed greater than 40 km/h (25 mph).

Conditions for Setting the DTC

Any of the following conditions may cause this DTC to set.

- The EBCM detects an open or shorted wheel speed sensor for 200 milliseconds.
- The EBCM detects a missing wheel speed sensor signal for 1 second. If more than one absent wheel speed sensor signal is detected, the condition must be present for 20 seconds to set DTCs.
- The EBCM detects an erratic wheel speed sensor signal for 40 continuous or cumulative milliseconds.

Action Taken When the DTC Sets

If equipped, the following actions occur.

- The EBCM disables the ABS.
- The EBCM disables the TCS.
- The EBCM disables DRP if all wheel speed inputs have failed.
- The ABS indicator turns ON.
- The ABS fault message is displayed.
- The traction fault message is displayed.
- The brake warning indicator turns ON, if DRP is disabled.
- The brakes message is displayed, if DRP is disabled.
- An ECE 13 response occurs.

Conditions for Clearing the DTC

The Conditions for Setting the DTC are no longer present and you use the scan tool Clear DTCs function.

Diagnostic Aids

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction.

If the customer's concern is that the ABS indicator is on only during humid conditions such as rain, snow or vehicle wash, thoroughly inspect the wheel speed sensor circuits for signs of water intrusion. Use the following procedure in order to help isolate the problem area:

1. Spray the suspected area with a 5 percent salt water solution.
2. Drive the vehicle at a speed greater than 19 km/h (12 mph) for at least 30 seconds.

Repair or replace the suspect harness if the DTC sets.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

3. If the DTC sets when the vehicle is not moving, the EBCM is detecting an open or shorted wheel speed sensor or wheel speed sensor circuit.
7. The front wheel speed sensors produce a high resolution signal. Therefore, the slightest rotation of the wheel causes the signal to toggle from high to low.