Diagnostic System Check - ABS. GMC Truck Export Savana 1998

For 1990-2009 cars

### 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 at terminal F (CKT 799) of the 10-way (C1) EBCM connector. The EBCM is supplied switched ignition voltage through terminal A (CKT 441), and ground is provided through terminal J (CKT 451).

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

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

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

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

6. This step decides between a faulty ABS safeguard indicator circuit and ABS indicator off always symptoms.

7. This step checks the electronic brake control lamp relay constant ground circuit.

8. This step decides between a faulty electronic brake control lamp relay and a faulty power/ground circuit to the relay.

9. This step decides between a faulty power or ground circuit to the electronic brake control lamp relay.

10. This step decides between a faulty ground circuit in the EBCM or in CKT 451.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---

1

1. Verify 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 Symptom and Diagnostic Trouble Code 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 three seconds and then turn off?

--

System is operating normally. Refer to Diagnostic Aids

Go to Step 11

4

1. Turn the ignition to OFF.
2. Disconnect the 10-way EBCM harness connector.
3. Turn the ignition to RUN.
4. Measure the voltage between the 10-way EBCM harness connector terminal A and ground using the J 39200 .

Is the voltage measured equal to or greater than the specified value?

10V

Go to Step 5

Go to Step 9

5

1. Turn the ignition to OFF.

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 10-way EBCM harness connector terminal J and the negative battery terminal.

Is the resistance measured within the specified range?

0-2ohms

Go to Step 6

Go to Step 20

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 Checking Terminal Contact in Electrical Diagnosis.

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? | -- | Refer to Electrical Diagnosis for serial data circuit diagnosis | --

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 10-way EBCM connector terminal A and the positive battery cable.

Is the resistance measured within the specified range?

0-2ohms

Go to Step 10

o to Step 22

10

1. Turn the ignition to OFF.
2. Remove the Brake Fuse 18.
3. Using the J 39200 , measure the resistance between the 10-way EBCM connector terminal A and ground.

Is the resistance measurement equal to the specified value?

OL

Go to Step 24

Go to Step 23

11 | Observe the ABS indicator lamp. Does the ABS indicator lamp stay on? | -- | Go to | Go to Step 12
12 | Disconnect the 10-way EBCM harness connector. Does the ABS indicator lamp stay on? | -- | Go to | Go to Step 13

13

1. Remove the antilock indicator relay from the socket.
2. Connect a 3-amp fused jumper between terminals A9 and B8.
3. Observe the ABS indicator lamp.

Does the ABS indicator lamp turn on?

--

Go to Step 14

Go to Step 20

14

1. Connect the 10-way EBCM harness connector.
2. Connect a J 39200 between terminal B9 and terminal A7.
3. Using the J 39200 , measure the voltage between terminal B9 and terminal A7.

Is the voltage measured within the specified range?

10V

Go to Step 19

Go to Step 15

15

1. Connect the J 39200 between terminal B9 and ground.
2. Using the J 39200 , measure the voltage between terminal B9 and ground.

Is the voltage measured within the specified range?

10V

Go to Step 16

Go to Step 17

16

1. Disconnect the 10-way EBCM harness connector.
2. Connect a J 39200 between terminal A7 in the relay socket and terminal K in the 10-way EBCM harness connector.
3. Using the J 39200 , measure the resistance between terminals A7 and K.

Is the resistance measured within the range specified in the Value(s) column?

0-2ohms

Go to Step 26

Go to Step 18

17 | Repair open or high resistance in CKT 441. Is the repair complete? | -- | Go to Step 1 | --
18 | Repair open or high resistance in CKT 451. Is the repair complete? | -- | Go to Step 1 | --
19 | Replace the antilock brake indicator relay. Is the repair complete? | -- | Go to Step 1 | --
20 | Repair open or high resistance in CKT 150. Is the repair complete? | -- | Go to Step 1 | --
21 | Repair open or high resistance in CKT 451. Is the repair complete? | -- | Go to Step 1 | --

22

1. Repair open or high resistance in CKT 441.
2. Check for an open in the Brake Fuse 18.

Is the repair complete?

--

Go to Step 1

--

23

1. Repair short to ground in CKT 441.
2. Check for an open in the Brake Fuse 18.

Is the repair complete?

--

Go to Step 1

--

24 | Inspect CKT 441 and the 10-way EBCM harness connector for physical damage which may result in a short to ground with the 10-way EBCM harness connector connected to the EBCM. Is there evidence of damage? | -- | Go to Step 25 | Go to Step 26
25 | Repair the terminals which are damaged. Is the repair complete? | -- | Go to Step 1 | --

26

1. Replace the EBCM.
2. Check for an open in Brake Fuse 18.

Is the repair complete?

--

Go to Step 1

--