GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Express 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C0238 or C038

Circuit Description

As the front wheels spin, the wheel speed sensors produce an AC signal. The EBCM uses the frequency of the AC signal to calculate the wheel speed. The PCM or vehicle speed sensor buffer (diesel) converts the data from the vehicle speed sensor to a 128k pulses/mile signal. The EBCM uses the vehicle speed signal from the PCM or VSSB in order to calculate the rear wheel speed.

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
    • The EBCM disables the ABS.
    • The ABS indicator turns ON.

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.

  1. If the front tires are not the same size as the rear tires, the EBCM calibration must match the FRONT tire size and the PCM calibration must match the REAR tire size. The VSSB must be replaced when the axle ratio or the rear tire size is changed significantly (diesel).

Step

Action

Yes

No

1

Did you perform the ABS Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - ABS

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

4

For vehicles equipped with gas engines, verify the EBCM and the 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 Powertrain Control Module Programming in Engine Controls - 4.3L, Powertrain Control Module Programming in Engine Controls - 5.0L and 5.7L or Powertrain Control Module Programming in Engine Controls - 8.1L.

For vehicles equipped with the 6.5L (L65) diesel engine, verify the correct VSSB is installed in the vehicle.

Did you find and correct the condition?

Go to Step 5

Go to Diagnostic Aids

5
  1. Use a scan tool in order to clear the DTCs.
  2. Operate the vehicle for 3.2 km (2 mi) within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK