GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Brakes 🢒 Antilock Brake System 🢒 Diagnostic System Check

Object Number: 339869 Size: LF
Antilock Brake System Component Views
Antilock Brake System Schematics

System Description

The diagnostic system check is an organized approach to identifying an Antilock Brake System (ABS) malfunction. The diagnostic system check must be the starting point for any ABS complaint diagnosis. The diagnostic system check directs the service technician to the next logical step in diagnosing the complaint.

Diagnostic serial data is transmitted/received by the EBCM through connector C2, terminal 5. The EBCM is supplied switched ignition voltage through connector C2, terminal 14, and ground is provided through connector C1, terminal 2.

Diagnostic Aids

Excessive resistance in the ground or power supply circuits will not allow communication with the EBCM. If communication with the EBCM is not possible, ensure that the ABS ground connection is good and that there is no excessive resistance in any of the power supply circuits.

Test Description

The numbers below refer to the steps in the diagnostic table:

  1. This step checks for normal ABS indicator lamp operation.

    2.

  2. This step checks for ignition voltage at the EBCM.

    3.

  3. This step checks for high resistance in the ground circuit.

    4.

  4. This step checks for high resistance in the ignition voltage circuit.

    5.

  5. This step checks for a short to ground in the ignition voltage circuit.

    6.

  6. This step checks for a short to ground in the EBCM.

Step

Action

Value(s)

Yes

No

1
  1. Ensure that all of the EBCM connectors are connected properly.
  2. Install the Scan Tool .
  3. Turn the ignition to RUN.
  4. Attempt to communicate with the EBCM using the Scan Tool .

Is data being received from the EBCM?

--

Go to Step  2

Go to Step  4

2

Using the Scan Tool , check for any DTCs.

Are any current or history DTCs displayed?

--

Go to DTC Table

Go to Step  3

3

  1. Turn the ignition to OFF for 10 seconds.
  2. Turn the ignition to RUN and observe the ABS indicator lamp.

Did the ABS indicator lamp turn on for two seconds and then turn off?

--

Go to Diagnostic Aids

Go to Step  11

4

  1. Turn the ignition to OFF.
  2. Disconnect the 24-way EBCM harness connector.
  3. Turn the ignition to RUN.
  4. Using the J 39200 , measure the voltage between the 24-way EBCM harness connector terminal 14 and ground .

Is the voltage measured within the specified range?

10-15 V

Go to Step  5

Go to Step  9

5

  1. Turn the ignition to OFF.

    2. Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

  2. Disconnect the negative battery cable.
  3. Using the J 39200 , measure the resistance between the 2-way EBCM harness connector terminal 2 and the negative battery terminal.

Is the resistance measured within the specified range?

0-2 ohms

Go to Step  6

Go to Step  12

6
  1. Inspect the EBCM terminals and the EBCM harness connector terminals for poor terminal contact.
  2. Inspect the battery terminals and the battery cable terminals for poor connection. Refer to Charging System Check in Engine Electrical.

Is the terminal contact or the connection poor?

--

Go to Step  7

Go to Step  8

7

Replace the terminals or repair the poor connection.

Is the repair complete?

--

Go to Step  1

--

8

Reconnect the EBCM connectors and the battery cables.

Are the EBCM connectors and the battery cables reconnected?

--

Go to Wiring Systems for Data Link Communications System Check

--

9

  1. Disconnect the positive battery cable.
  2. Turn the ignition to RUN. (This is to provide circuit continuity.)
  3. Using the J 39200 , measure the resistance between the 24-way EBCM connector terminal 14 and the positive battery cable.

Is the resistance measured within the specified range?

0-2 ohms

Go to Step  10

Go to Step  13

10

  1. Turn the ignition to OFF.
  2. Remove circuit breaker.
  3. Remove the ABS indicator lamp relay.
  4. Using the J 39200 , measure the resistance between the 24-way EBCM connector terminal 14 and ground.

Is the resistance measurement equal to the specified value?

OL

Go to Step  15

Go to Step  14

11

Observe the ABS indicator lamp.

Does the ABS indicator lamp stay on?

--

Go to ABS Indicator Always On

Go to ABS Indicator Inoperative

12

Repair open or high resistance in CKT 150.

Is the repair complete?

--

Go to Step  1

--

13
  1. Repair open or high resistance in CKT 341.
  2. Inspect for an open in circuit breaker.

Is the repair complete?

--

Go to Step  1

--

14
  1. Repair short to ground in CKT 341.
  2. Inspect for an open in the circuit breaker.

Is the repair complete?

--

Go to Step  1

--

15

Inspect CKT 341 and the 24-way EBCM harness connector for physical damage which may result in a short to ground with the 24-way EBCM harness connector connected to the EBCM.

Is there evidence of damage?

--

Go to Step  16

Go to Step  17

16

Repair the terminals which are damaged. Refer to Repairing Connector Terminals .

Is the repair complete?

--

Go to Step  1

--

17
  1. Replace the EBCM. Refer to Electronic Brake Control Module Replacement .
  2. Inspect for an open in the circuit breaker.

Is the repair complete?

--

Go to Step  1

--