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 appropriate table (below) for Gas, or Diesel engines.
Diagnostic serial data is transmitted/received by the EBCM through connector C1, terminal G. The EBCM is supplied switched ignition voltage through connector C1, terminal A, and ground is provided through connector C1, terminal J.
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 short to ground.
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This step checks for high resistance in the ground 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 checks for a short to ground dued to the EBCM.
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This step checks for a proper voltage source before the IP Fuse Block.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
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 Step 3 | |
Did the ABS indicator lamp turn on for two seconds and then turn off? | -- | System is operating normally. Go to Diagnostic Aids. | Go to Step 11 | |
Is the voltage measured within the specified range? | 10-15 V | Go to Step 7 | Go to Step 5 | |
Is the resistance measurement equal to the specified value? | OL | Go to Step 6 | Go to Step 14 | |
6 | Inspect the BRAKE Fuse #18 from the IP Fuse Block. Is the fuse open? | -- | Go to Step 15 | Go to Step 17 |
Using a J 39200 , measure the resistance between the 10-way EBCM connector terminal J and ground. Is the resistance measurement equal to the specified range? | 0-2 ohms | Go to Step 8 | Go to Step 12 | |
8 |
Is the terminal contact or the connection poor? | -- | Go to Step 9 | Go to Step 10 |
9 | Replace the terminals or repair the poor connection. Is the repair complete? | -- | Go to Step 1 | -- |
10 | Reconnect the EBCM connectors and the battery cables. Are the EBCM connectors and the battery cables reconnected? | -- | -- | |
Observe the ABS indicator lamp. Does the ABS indicator lamp stay on? | -- | Go to ABS Indicator Always On | ||
12 | Repair open or high resistance in CKT 150. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 1 | -- |
13 | Repair the open or high resistance in CKT 441. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 1 | -- |
14 | Repair the short to ground in CKT 441. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 1 | -- |
Is the fuse open? | -- | Go to Step 16 | Go to Step 1 | |
16 |
Is the repair complete? | -- | Go to Step 1 | -- |
Is the voltage measurement equal to the specified range? | 10-15 V | Go to Step 13 | Go to Step 18 | |
18 | Repair the open, high resistance, or short to ground in CKT 300. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 1 | -- |
