Circuit Description
As the front wheels spin, the wheel speed sensors (WSSs) produce an AC signal. The electronic brake control module (EBCM) uses the frequency of the AC signal to calculate the wheel speed. The powertrain control module (PCM) converts the data from the vehicle speed sensor (VSS) to a 128k pulses/mile signal. The EBCM uses the vehicle speed signal from the PCM in order to calculate the rear wheel speed.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C0238 Wheel Speed Mismatch
Conditions for Running the DTC
The ignition is ON and the vehicle speed is between 24 km/h (15 mph) and 80 km/h (50 mph).
Conditions for Setting the DTC
The EBCM detects that one wheel speed input is 10 percent greater than or 10 percent less than the other wheel speed inputs within 3.2 km (2 mi) of driving.
Action Taken When the DTC Sets
If equipped, the following actions occur:
| • | The EBCM disables the ABS/TCS/DRP. |
| • | The ABS indicator turns ON. |
| • | The TRACTION OFF indicator turns ON. |
| • | The red brake warning indicator turns ON. |
| • | The DIC displays the SERVICE BRAKE SYSTEM message. |
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
Installing one tire of significantly different size on the vehicle causes DTC C0238 to set. Operating the vehicle with a tire that has very low air pressure may also set this DTC. Inspect the vehicle for an incorrect or damaged wheel speed sensor or vehicle speed sensor if the tires and the EBCM and PCM calibrations are OK.
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Yes | No |
|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 | Inspect both of the front tires on the vehicle to ensure that both tires are of equal size. Are both of the front tires of equal size? | Go to Step 3 | Go to Diagnostic Aids |
3 | Inspect both of the rear tires on the vehicle to ensure that both tires are of equal size. Are both of the rear tires of equal size? | Go to Step 4 | Go to Diagnostic Aids |
Verify the electronic brake control module (EBCM) and the powertrain control module (PCM) both have the correct tire size calibration. Use the scan tool in order to view the EBCM tire size calibration or perform the Tire Size Calibration procedure and refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you find and correct the condition? | Go to Step 5 | Go to Diagnostic Aids | |
5 |
Does the DTC reset? | Go to Step 2 | System OK |
