GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Body 🢒 Wiring Systems 🢒 Diagnostic System Check - Air ABS

Circuit Description

The ABS Diagnostic System Check is an organized approach to identifying problems associated with the ABS. This must be the starting point for any ABS related concern and will direct you to the next logical step in diagnosing a malfunction. Most system malfunctions are linked to faulty wiring, connections and occasionally, to components. Understanding the ABS system and using the diagnostic tables correctly will reduce diagnostic time and prevent unnecessary parts replacement.

Test Description

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

  1. Lack of communication may be due to partial or total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.

    2.

  2. The presence of DTCs that begin with a "U" indicates that some other module is not communicating. The specified procedure will compile all of the available information before tests are performed.

    3.

  3. A flashing or inoperative green VLT LED indicates a fault in the ignition 3 voltage or ground circuits to the EBCM. During normal operation, the green VLT LED is always illuminated when the ignition is ON.

    4.

  4. An illuminated ECU LED indicates a fault in the ignition 3 voltage or ground circuits to the EBCM or an EBCM internal malfunction. This fault must be repaired prior to proceeding with any other fault diagnosis.

    5.

  5. The EBCM does not display faults that are not current.

Step

Action

Yes

No

1

Install a scan tool.

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up in Data Link Communications

2

  1. Turn the ignition ON.
  2. Use the scan tool in order to establish communication with the following modules:
    3. • Serial Data Gateway
    • Powertrain
    • Instrument Panel Cluster
    • Supplemental Inflatable Restraint

Does the scan tool communicate with all of the control modules listed above?

Go to Step 3

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

3

Use the scan tool in order to display DTCs for the following control modules:

    • Serial Data Gateway
    • Powertrain
    • Supplemental Inflatable Restraint

Does the scan tool display any DTCs for the control modules listed above?

Go to Step 4

Go to Symptoms - Air Antilock Brake System

4

Does the scan tool display any DTCs that begin with a "U"?

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

Go to Step 5

5

Observe the LEDs on the EBCM after the ignition has been ON for 10 seconds.

Is the green VLT LED ON steady?

Go to Step 2

Go to Green VLT Status Lamp Inoperative

6

Does the EBCM display an illuminated red ECU LED?

Go to Status Lamps Illuminated - Engine Control Unit

Go to Step 3

7

Does the EBCM display any other illuminated red LEDs?

Go to Status Lamps Reference Table

Go to Step 4