GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Savana 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C0235-C0237, C035-C037, or P1504

Circuit Description

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

C0235

The ignition is ON.

C0236 and C0237

    • The ignition is ON.
    • The vehicle speed is greater than 32 km/h (20 mph) when the brake is applied or 19 km/h (12 mph) when the brake is released.

P1504

    • The ignition is ON.
    • The vehicle is not moving.

Conditions for Setting the DTC

C0235

The EBCM detects low voltage on the vehicle speed signal circuit for 500 milliseconds.

C0236

The rear wheel speed signal is less than 6 km/h (4 mph) for 5 seconds, or 120 seconds in order to set multiple missing sensor signal DTCs.

C0237

The EBCM detects an erratic rear wheel speed signal for 105 milliseconds.

P1504

The PCM detects low voltage on the vehicle speed signal circuit for 45 seconds.

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

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to the following:

    •  Testing for Electrical Intermittents
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs
    •  Connector Repairs

Test Description

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

  1. This step tests for a voltage signal from the PCM or the VSSB (diesel).

    2.

  2. This step tests for a missing or erratic vehicle speed signal from the PCM or VSSB. An assistant may be required in order to perform this test.

Step

Action

Values

Yes

No

Schematic Reference: Antilock Brake System Schematics

1

Did you perform the ABS Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - ABS

2
  1. Use a scan tool in order to clear the DTCs.
  2. Operate the vehicle at a speed greater than the specified value.

Does the DTC set?

19 km/h (12 mph)

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn OFF the ignition.
  2. Disconnect from the EBCM, the harness connector which contains the vehicle speed signal circuit.
  3. Turn ON the ignition.
  4. Use a DMM in order to measure the DC voltage between the vehicle speed signal circuit and a good ground.

Does the voltage measure greater than the specified value?

10 V

Go to Step 4

Go to Step 7

4

  1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Place the transmission in neutral.
  3. Set up the DMM in order to measure the DC voltage between the vehicle speed signal circuit and a good ground.
  4. Spin the rear wheels as fast as possible by hand for at least 30 seconds and while ensuring the driveshaft is rotating, observe the DMM.

Does the voltage measure within the specified range the entire time the driveshaft is rotating?

5-7 V

Go to Step 5

Go to Step 7

5

Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 6

6

Replace the EBCM. Refer to Electronic Brake Control Module Replacement .

Important: Use the scan tool in order to perform the Tire Size Calibration procedure.

Did you complete the replacement?

--

Go to Step 10

--

7

Test the vehicle speed signal circuit for an open, a short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems

Did you find and correct the condition?

--

Go to Step 10

Go to Step 8

8

Inspect for poor connections at the harness connector of the PCM or vehicle speed sensor (VSS) buffer. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 9

9

Important: Perform the setup procedure for the PCM (gas vehicles only).

Replace the PCM or VSS buffer. Refer to Powertrain Control Module Replacement in Engine Controls - 4.3L, Powertrain Control Module Replacement in Engine Controls - 5.0L and 5.7L, Vehicle Speed Sensor Buffer Replacement in Instrument Panel, Gages, and Console or Powertrain Control Module Replacement in Engine Controls - 8.1L.

Did you complete the replacement?

--

Go to Step 10

--

10
  1. Use the scan tool in order to clear the DTC.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 3

System OK