GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 Brakes 🢒 Antilock Brake System 🢒 ABS Indicator Always On

Object Number: 191458 Size: MF
ABS Components
Antilock Brake System Schematics

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.

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), there is a short to ground in CKT 867 between the instrument cluster and the EBCM or the EBCM is internally shorted to ground.

Test Description

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

  1. This step checks for a short to ground in CKT 867.

Step

Action

Value(s)

Yes

No

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check

2
  1. Turn the ignition to OFF.
  2. Disconnect the 10-way EBCM harness connector from the EBCM.
  3. Turn the ignition to RUN.

Does the ABS indicator lamp turn on?

--

Go to Step 3

Go to Step 4

3

Repair the short to ground in CKT 867.

Is the repair complete?

--

Go to Diagnostic System Check

--

4
  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 5

Malfunction is intermittent. Go to Diagnostic Aids

5

Replace the EBCM.

Is the repair complete?

--

Go to Diagnostic System Check

--