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 because it directs the service technician to the next logical step in diagnosing the complaint. Failure to perform the Diagnostic System Check will result in extended diagnostic time, incorrect diagnosis and parts replacement.
The EBCM is supplied battery voltage (through the ABS relay) to terminal K1 and terminal K2. Ground is provided through terminal A1, terminal A2 and the ground clip on the EBCM chassis.
Diagnostic Aids
Excessive resistance in the signal ground or ignition power circuit will not allow communication with the EBCM. If communication with the EBCM is not possible, ensure that the ABS signal ground connection is good and that there is no excessive resistance in the ignition power circuit.
Test Description
An example test description follows:
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This test will by-pass the ABS indicator relay in order to help isolate the malfunction.
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This test checks the ABS indicator lamp and the wiring in order to help isolate the malfunction.
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This test isolates the malfunction to either a shorted ABS indicator lamp relay coil or a wire shorted to voltage.
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This test measures the voltage present at the EBCM.
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This test measures the voltage present at the ABS relay contacts.
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This test checks for a malfunctioning EBCM. If the red diagnostic status lamp is on, the voltage available to the EBCM is either below 9 V or above 9 V.
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If the 30 amp ABS fuse is open, a short to ground in CKT 1442, or an internal short in the ABS relay is indicated.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Turn the ignition to RUN and observe the ABS indicator lamp. Does the ABS indicator lamp turn on, flash twice, then remain on? | -- | Go to Step 3 | Go to Step 2 | ||||||
2 | Does the ABS indicator lamp turn on, and remain on without flashing. | -- | Go to Step 11 | Go to Step 4 | ||||||
3 | Drive the vehicle at speeds above 16 km/h (10 mph) while observing the ABS indicator lamp. Does the ABS indicator lamp remain on? | -- | Go to Step 11 | Go to Diagnostic Aids. | ||||||
4 |
Observe the ABS indicator lamp, is the ABS lamp on? | -- | Go to Step 6 | Go to Step 5 | ||||||
Is the ABS indicator lamp open? | -- | Go to Step 30 | Go to Step 31 | |||||||
6 |
Is the voltage measured within the specified range? | 11-16 V | Go to Step 7 | Go to Step 8 | ||||||
7 |
Is the resistance measured within the specified range? | 0-2 ohms | Go to Step 9 | Go to Step 35 | ||||||
8 | Inspect the circuit breaker #9. Is the circuit breaker closed? | -- | Go to Step 32 | Go to Step 33 | ||||||
9 |
Is the ABS indicator lamp on? | -- | Go to Step 34 | Go to Step 10 | ||||||
10 |
Is the resistance measured equal to the specified value? | OL | Go to Step 36 | Go to Step 37 | ||||||
11 | Observe the diagnostic status lamp window on the side of the EBCM. Is the green VOLT status lamp on? | -- | Go to Step 12 | Go to Step 13 | ||||||
12 | Is the green VOLT status lamp flashing? | -- | Go to Step 20 | Go to Step 14 | ||||||
13 |
Are any red diagnostic status lamps on? | -- | Go to Step 34 | Go to Step 20 | ||||||
14 | Observe the diagnostic status lamp window on the side of the EBCM. Are any red diagnostic status lamps on? | -- | Go to Step 28 | Go to Step 15 | ||||||
Is the ABS indicator lamp off? | -- | Go to Step 34 | Go to Step 16 | |||||||
16 | Remove and inspect the jumper wire fuse. Is the fuse open? | -- | Go to Step 18 | Go to Step 17 | ||||||
17 | Remove the ABS indicator lamp relay from the relay center. Is the ABS indicator lamp on? | -- | Go to Step 39 | Go to Step 19 | ||||||
Is the resistance measured equal to the specified value? | OL | Go to Step 38 | Go to Step 36 | |||||||
19 | Using a J 39200 , measure the voltage between terminal 85 of the relay center #1 and ground. Is the voltage measured within the specified range? | 11-14 V | Go to Step 36 | Go to Step 32 | ||||||
Is the voltage measured within the specified range? | 11-14 V | Go to Step 34 | Go to Step 21 | |||||||
21 |
Are both resistance measurements within the specified range? | 0-2 ohms | Go to Step 22 | Go to Step 40 | ||||||
22 | Using a J 39200 , measure the voltage of the vehicle battery. Refer to the Battery section. Is the voltage measured within the specified range. | 11.5-14 V | Go to Step 23 | Go to Battery section. | ||||||
Is the voltage measured within the specified range? | 11-14 V | Go to Step 25 | Go to Step 24 | |||||||
24 |
Is the fuse open? | -- | Go to Step 41 | Go to Step 42 | ||||||
25 |
Is the resistance measured within the specified range? | 0-2 ohms | Go to Step 26 | Go to Step 43 | ||||||
26 |
Is the voltage measured within the specified range? | 11-14 V | Go to Step 27 | Go to Step 44 | ||||||
27 |
Is the resistance measured within the specified range? | 0-2 ohms | Go to Step 45 | Go to Step 35 | ||||||
Observe the diagnostic status lamps on the side of the EBCM. Is the red ECU lamp on? | -- | Go to Step 20 | Go to Step 29 | |||||||
29 | Observe the diagnostic status lamps on the side of the EBCM. There should be a minimum of three diagnostic status lamps on:
Are there three diagnostic status lamps on? | -- | Go to the EBCM Diagnostic Status Lamps Table | Go to Step 34 | ||||||
30 | Replace the ABS indicator lamp Refer to Body and Chassis in Instrument Panel and Gauges. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
31 | Repair the open or high resistance in CKT 38 or CKT 404. Is the the broken wire or high resistance condition repaired? | -- | Go to Step 1 | -- | ||||||
32 | Repair the open or high resistance in CKT 145 or CKT 406. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
33 |
Is the repair complete? | -- | Go to Step 1 | -- | ||||||
34 |
Is the malfunction still present? | -- | Go to Step 46 | Go to Diagnostic Aids | ||||||
35 | Repair the open or high resistance in CKT 150. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
36 | Replace the ABS indicator lamp relay. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
37 | Repair the short to ground in CKT 1899. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
38 | Repair the short to voltage in CKT 1899. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
39 | Repair the short to ground in CKT 38 or CKT 404. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
40 | Repair the open or high resistance in CKT 1651. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
Check for a short to ground in CKT 1442 or a shorted ABS relay. Is the repair complete? | -- | Go to Step 1 | -- | |||||||
42 | Repair the open or high resistance in CKT 1442. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
43 | Repair the open or high resistance in CKT 839. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
44 | Repair the open or high resistance in CKT 139 or CKT 145. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
45 | Replace the ABS relay. Is the repair complete? | -- | Go to Step 1 | -- | ||||||
46 | Replace the EBCM. Is the repair complete? | -- | System OK | -- |
