ABS Indicator Always On. GMC Truck Export Savana 1998

For 1990-2009 cars

### Circuit Description

The EBCM controls the ANTILOCK indicator lamp illumination by supplying a ground to terminal B. When the vehicle is started or the ignition is turned to the RUN position, the ANTILOCK indicator should illuminate for three seconds and turn off. A ground will also be supplied to the ABS indicator lamp through contacts A9 and B8 of the electronic brake control lamp relay if the 10-way EBCM connector is unseated or disconnected.

### Diagnostic Aids

If the ANTILOCK indicator lamp is on always with no DTCs set (never turns off after three seconds with the vehicle started or with the ignition switch in the RUN position), check for the proper connection of the 10-way EBCM harness connector. Check for a failed electronic brake control lamp relay. If no problems are found, then there could be a short to ground in CKT 867 between the instrument cluster and the EBCM, or an open in the power or ground circuits to the electronic brake control lamp relay, or the EBCM is internally shorted to ground on C1 terminal B, or open internally on C1 terminal K.

### Test Description

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

1. This step removes the ABS safeguard indicator circuitry from consideration as the cause of the fault.

2. This step checks the ground circuit from the EBCM to the electronic brake control lamp relay.

3. This step decides between a faulty ground in the EBCM terminal K or CKT 451.

4. This step decides between a faulty electronic brake control lamp relay, or an open in CKT 441.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Diagnostic System Check performed? | -- | Go to Step 2 | Go to
2 | Make sure that the 10-way EBCM harness connector is securely connected and free of damage. Is the 10-way EBCM harness connector securely connected and free of damage? | -- | Go to Step 3 | Go to Step 12
3 | Remove the antilock brake indicator relay. Does the ABS indicator lamp remain on? | -- | Go to Step 7 | Go to Step 4
4 | Using a J 39200 , test for continuity between terminal A7 in the antilock brake indicator relay socket and chassis ground. Is the resistance measured within the range specified? | 0-2ohms | Go to Step 6 | Go to Step 5

5

1. Disconnect the 10-way EBCM harness connector from the EBCM.
2. Using a J 39200 , test for continuity between terminal A7 in the antilock brake relay socket and terminal K in the 10-way EBCM harness connector

Is the resistance within the range specified?

0-2ohms

Go to Step 11

Go to Step 10

6 | Using a J 39200 , test for voltage between terminal B9 in the antilock brake indicator relay socket and chassis ground. Is the voltage measured within the range specified? | Greater than 10V | Go to Step 9 | Go to Step 8

7

1. Inspect CKT 867 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.
2. Reconnect all the connectors.
3. Clear all the DTCs using the scan tool.
4. Test drive the vehicle above 16 km/h (10 mph).

Is the ABS indicator lamp on constantly?

--

Go to Step 11

Refer to Diagnostic Aids

8 | Repair the open in CKT 441. Refer to Wiring Repairs . Is the repair complete? | -- | Go to | --
9 | Replace the antilock brake indicator relay. Is the repair complete? | -- | Go to | --
10 | Repair the open in CKT 451. Refer to Wiring Repairs . Is the repair complete? | -- | Go to | --
11 | Replace the EBCM. Refer to . Is the repair complete? | -- | Go to | --
12 | Repair any damage to the 10-way EBCM harness connector and securely connect the connector. Refer to . Is the repair complete? | -- | Go to | --