GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The EBCM receives the rear wheel speed signal from the VCM (4.3L only) or the PCM. The signal from the VCM/PCM is always high (12 Volts) when the ignition is on and the vehicle is not moving. When the vehicle is moving, the VCM/PCM toggles this voltage on and off. The EBCM uses the frequency of this signal to calculate the rear wheel speed.

Conditions for Running the DTC

    • The ignition is ON.
    • The front wheel speed sensor signals are both greater than 13 km/h (8 mph).

Conditions for Setting the DTC

The rear wheel speed sensor signal is less than 6 km/h (4 mph) for 5 seconds.

Action Taken When the DTC Sets

    • The ABS, BRAKE and TRACTION OFF (if equipped with traction control) indicators are commanded on.
    • The ABS, DRP and Traction Control (if equipped) are disabled for as long as the malfunction is present.

Conditions for Clearing the DTC

    • The condition(s) responsible for setting the DTC are no longer present.
    • A scan tool is used in order to clear the DTC.

Important: After the DTC is cleared and the ignition is ON, the ABS indicator may remain on until the EBCM completes a power-up self-test. This test concludes when the vehicle reaches a speed of greater than 13 km/h (8 mph) and the wheel speeds are verified by the EBCM.

Diagnostic Aids

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to Testing for Intermittent Conditions and Poor Connections , Wiring Repairs and Connector Repairs in Wiring Systems.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step tests if the VCM/PCM is sending a vehicle speed signal to the EBCM. The voltage should measure approximately 50% of battery voltage while the driveshaft is rotating.

Step

Action

Value(s)

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

2

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

Does the DTC set?

--

Go to Step 3

Go to Diagnostic Aids

3

  1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Turn the ignition OFF.
  3. Disconnect from the EBCM, the harness connector which contains the vehicle speed signal circuit.
  4. Connect a DMM between the vehicle speed signal circuit (at the harness connector) and a good ground.
  5. Set up the DMM to measure DC voltage.
  6. Place the transmission shift lever in neutral.
  7. Turn the igniton ON.
  8. Spin the rear wheels as fast as is possible by hand and while ensuring that the driveshaft is rotating, observe the DMM.

Does the voltage measure within the specified value?

5-7 volts

Go to Step 5

Go to Step 4

4

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

Did you find and correct the condition?

--

Go to Step 9

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 9

Go to Step 6

6

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

Important: Perform the Tire Size Calibration procedure.

Did you complete the replacement?

--

Go to Step 9

--

7

Inspect for poor connections at the harness connector of the VCM/PCM. 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 9

Go to Step 8

8

Important: Perform the setup procedure for the VCM/PCM.

Replace the VCM/PCM. Refer to VCM Replacement/Programming in Engine Controls-4.3L or Powertrain Control Module Replacement in Engine Controls-4.8L, 5.3L, and 6.0L.

Did you complete the replacement?

--

Go to Step 9

--

9

  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 set?

--

Go to Step 3

System OK