Circuit Description
The amber ABS indicator lamp operates in two modes; normal and backup. In the normal mode, ignition voltage is supplied to the ABS indicator lamp bulb through the IGN SW fuse. Once the ignition is turned on or the vehicle is started the EBCM energizes the ABS indicator lamp relay (normally closed) and ground path for the light through the relay is opened. The EBCM also illuminates the ABS indicator lamp for a 2 second bulb check by suppling ground through connector C2, terminal 1, If the EBCM senses a failure and a DTC is set, it will illuminate the lamp in this manner. In the backup mode, the ABS telltale relay circuit will ensure that the ABS indicator lamp is illuminated if the 24-way connector is disconnected or poorly seated, or if certain EBCM internal failures during normal operation. If either of these conditions occur, the ABS indicator lamp relay closes, which creates an alternate ground path to the ABS indicator lamp circuit through terminal B8 and terminal A7 of the EBCM. This system ensures that the ABS indicator lamp will always be turned on if the following conditions exist:
| • | Short to ground in CKT 867 |
| • | Open or high resistance in CKT 1899 |
| • | Open or high resistance in CKT 39 |
| • | The ABS telltale relay is faulty |
| • | The EBCM is faulty |
Diagnostic Aids
If the ABS indicator lamp is on always with no DTCs set (never turns off 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 there is a fault in the ABS telltale relay circuit.
Test Description
The numbers below refer to the steps in the diagnostic table:
-
This step checks for normal operation of the ABS indicator lamp.
-
This step manually (with fused jumper) turns off the ABS indicator lamp.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Diagnostic System Check performed? | -- | Go to Step 2 | |
Does the ABS indicator lamp turn off? | -- | Go to Step 6 | Go to Step 3 | |
Does the ABS indicator lamp turn off? | -- | Go to Step 4 | Go to Step 7 | |
4 | Using a J 39200 , measure the voltage between the ABS indicator relay harness connector terminal C1 and ground. Is the voltage measured equal to or greater than the specified value? | 10 V | Go to Step 5 | Go to Step 8 |
5 | Using a J 39200 , measure the resistance between the relay center harness connector terminal C2 and the EBCM harness connector terminal 2. Is the resistance within the specified range? | 0-2 ohms | Go to Step 9 | Go to Step 10 |
6 |
Inspect CKT 1899 for damage that could result in an open circuit. Repair damage if evident. Replace the terminals if poor contact or corrosion exists. Is the ABS indicator lamp on constantly? | -- | Go to Step 11 | Go to Diagnostic Aids |
7 | Repair the short to ground in CKT 867. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |
8 | Repair the open or the high resistance in CKT 341. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |
9 | Replace the ABS indicator relay. Is the repair complete? | -- | -- | |
10 | Repair the open or the high resistance in CKT 1899. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |
11 | Replace the EBCM. Refer to Electronic Brake Control Module Replacement . Is the repair complete? | -- | -- |
