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. Refer to the table below.
Diagnostic serial data is transmitted/received by the EBCM through connector C1, terminal G. The EBCM is supplied battery voltage through connector C3, terminal A and switched ignition voltage through connector C1, terminal A. Grounds are provided through connectors C1, terminal J, and C3 terminal B.
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:
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This step checks for normal ABS indicator lamp operation.
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This step checks for ignition voltage at the EBCM.
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This step checks for high resistance in the ground circuit.
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This step checks for high resistance in the ignition voltage circuit.
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This step checks for a short to ground in the ignition voltage circuit.
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This step decides between ABS indicator lamp on always, or off always as the symptom.
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This step decides between a short to ground in the 10-way EBCM harness/connector, or an internal EBCM fault.
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Using the scan tool, this step attempts to show that the EBCM can control turning the ABS indicator lamp off, but the instrument cluster is not responding.
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Using the scan tool, this step attempts to show that the EBCM can control turning the ABS indicator lamp on, but the instrument cluster is not responding.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Is data being received from the EBCM? | -- | ||
2 | Using the Scan Tool , check for any DTCs. Are any current or history DTCs displayed? | -- | Go to Symptom and Diagnostic Trouble Code Table | |
Did the ABS indicator lamp turn on for two seconds and then turn off? | -- | Go to Diagnostic Aids | ||
Is the voltage measured within the specified range? | 10-15V | |||
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. Is the resistance measured within the specified range? | 0-2ohms | |||
6 |
Is the terminal contact or the connection poor? | -- | ||
7 | Replace the terminals or repair the poor connection. Is the repair complete? | -- | -- | |
8 | Reconnect the EBCM connectors and the battery cables. Are the EBCM connectors and the battery cables reconnected? | -- | Go to Data Link Communications for serial data circuit diagnosis | -- |
Is the resistance measured within the specified range? | 0-2ohms | |||
Is the resistance measurement equal to the specified value? | OL | |||
Observe the ABS indicator lamp. Does the ABS indicator lamp stay on? | -- | |||
12 | Repair open or high resistance in CKT 451. Is the repair complete? | -- | -- | |
13 |
Is the repair complete? | -- | -- | |
14 |
Is the repair complete? | -- | -- | |
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? | -- | |||
16 | Repair the terminals which are damaged. Is the repair complete? | -- | -- | |
17 |
Is the repair complete? | -- | -- | |
Using the Scan Tool from the Special Functions screen, turn the ABS indicator off. Did the ABS indicator turn off? | -- | |||
19 | Replace the EBCM. Is the repair complete? | -- | -- | |
Using the Scan Tool from the Special Functions screen, turn the ABS indicator on. Did the ABS indicator turn on? | -- |
