Diagnostic Strategies

Intermittent failures in the anti-lock brake system may be difficult to accurately diagnose. The ABS diagnostic trouble codes which may be stored by the EBCM are not designated as Current or History diagnostic trouble codes. These diagnostic trouble codes can be helpful in diagnosing intermittent conditions.

If an intermittent condition is being diagnosed, the ABS system can be used in the following manner to help isolate the suspected circuit.

1. Display, then clear any ABS diagnostic trouble codes present in the EBCM.
2. Test drive vehicle, attempting to repeat failure condition. A description of driving conditions under which the last failure occurred can be helpful.
3. After duplicating condition, stop the vehicle, then display any diagnostic trouble codes stored.
4. If no diagnostic trouble codes were stored, proceed to Troubleshooting or to Symptom Diagnosis Charts.
5. If a diagnostic trouble code was stored, check electrical connections and wiring for the following:

a. Poor mating of connector halves.
b. Terminals not fully seated in connector halves.
c. Improperly formed, or damaged terminals. All connector terminals in a problem circuit should be carefully reformed to increase contact tension.
d. Poor terminal to wire connection. In most cases, this will require removing wire from connector body.
6. If a complaint of intermittent warning lamp operation is encountered, the following circuits to the EBCM should be checked:
a. Low system voltage. If low voltage is detected at the EBCM/EBTCM, the Anti-lock lamp will illuminate until normal operating voltage is detected.
b. Low brake fluid. This condition in the Pressure Modulator Valve (PMV) reservoir will cause the "Brake and "Anti-lock lamps to illuminate. When an acceptable fluid level is registered, the lamps will no longer be illuminated.
7. Any condition which results in interruption of power to the EBCM/EBTCM or hydraulic unit may cause the warning lamps to turn on intermittently. These circuits include the main relay, pump motor relay, fuses and related wiring.