Notes On INTERMITTENTS

As with virtually any electronic system, intermittent failures in the Anti-Lock Brake system may be difficult to accurately diagnose. In order to utilize the ABS self diagnostic capability, the failure must occur during the ignition cycle in which diagnosis is being attempted. Once an ABS trouble code is set, it remains set until the ignition is turned off.

The Electronic Brake Control Module tests for different failures under different vehicle conditions; for this reason, it is often necessary to perform the test drive procedure to repeat the failure and allow an ABS code to set. See TEST DRIVING ABS COMPLAINT VEHICLES  .

If the system malfunction is not repeated during the test drive, a good description of vehicle behavior may be helpful in locating a "most likely" component or circuit. The symptom index table may also be useful in isolating the failure. See SYMPTOM INDEX  table under SYSTEM TESTS. Most intermittent problems are caused by faulty electrical connections or wiring. When an intermittent failure is encountered, check suspect circuits for:

• Poor mating of connector halves or terminals not fully seated in the connector body (backed out).
• Improperly formed or damaged terminals. All connector terminals in a problem circuit should be carefully reformed to increase contact tension.
• Poor terminal to wire connection. This requires removing the terminal from the connector body to inspect.

If a visual check does not find the cause of the problem, operate the car with the EBCM connected in an attempt to duplicate the condition and set an ABS trouble code.

Most failures of the Anti-Lock Brake System will disable anti-lock function for the entire ignition cycle, even if the fault clears before key-off. There are a few failure conditions, however, which will allow ABS operation to resume during the ignition cycle in which a failure occurred if the failure conditions are no longer present.

The following conditions may result in intermittent operation of the BRAKE indicator lamp and/or ANTI-LOCK DISABLED message. All other failures will cause the BRAKE indicator lamp and/or ANTI-LOCK DISABLED message to remain on until the ignition switch is turned off and then back on. Circuits involving these inputs to the EBCM should be investigated if a complaint of intermittent warning system operation is encountered.

• If low system voltage is detected at the EBCM, the ABS will illuminate the ANTI-LOCK DISABLED message until normal system voltage is achieved. Once normal voltage is seen at the EBCM, normal operation resumes.
• A low brake fluid condition will cause the ABS to turn on the BRAKE indicator lamp and ANTI-LOCK DISABLED message. When the fluid level sensor again indicates an acceptable fluid level, normal operation will resume.
• Low accumulator pressure will cause both the BRAKE indicator lamp and the ANTI-LOCK DISABLED message to be displayed. Once normal operating pressure is achieved, the lamp and message will be turned off and the system will operate normally.

Additionally, any condition which results in interruption of power to the EBCM or hydraulic unit may cause the BRAKE indicator lamp and the ANTI-LOCK DISABLED message to illuminate intermittently. These circuits include the overvoltage protection relay and related wiring and fuses.