Diagnostic Strategies
As with virtually any electronic system, intermittent failures are difficult to accurately diagnose. The diagnostic trouble codes stored by the EBCM are not specifically designated as "Current" or "History" diagnostic trouble codes, as are PCM diagnostic trouble codes. These diagnostic trouble codes, however, can be helpful in diagnosing intermittent conditions.
When an instrument condition is being diagnosed, use the EBCM's self-diagnostic system in the following manner to help isolate the suspect circuit:
1. Display and clear any diagnostic trouble codes which may be present in the EBCM.
2. Test drive the vehicle, attempting to repeat the failure condition. When available, a description of the driving circumstances under which the failure occurred can be helpful in duplicating the condition.
3. Stop the vehicle and display any diagnostic trouble codes which have been stored.
^ When diagnostic trouble codes are stored, use the "Diagnostic Trouble Code Guide" chart in this section to identify and isolate suspect circuits.
^ When no diagnostic trouble codes are stored, it becomes necessary to use symptom diagnosis.
When the system malfunction is not repeated during the test drive, a good vehicle behavior description is helpful in locating a "most likely" component or circuit. The "Diagnostic Symptom Guide" chart in this section is also useful in isolating the failure.
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).
^ Dirt or corrosion on the terminals. The terminals must be clean and free of any foreign material which could impede proper terminal contact.
^ Damaged connector body, exposing the terminals to moisture and dirt, as well as not maintaining proper terminal orientation with the component or mating connector.
^ Improperly formed or damaged terminals. All connector terminals in problem circuits should be checked carefully to ensure good contact tension. Use a corresponding mating terminal to check for proper tension. Refer to "Checking Terminal Contact" in this section for the specific procedure.
^ The J 35616-A Connector Test Adapter Kit must be used whenever a diagnostic procedure requests checking or probing a terminal. Using the adapter ensures that no damage to the terminal will occur, as well as giving an idea of whether contact tension is sufficient. If contact tension seems incorrect, refer to "Checking Terminal Contact" in this section for specifics.
^ Poor terminal-to-wire connection. Checking this requires removing the terminal from the connector body. Some conditions which fall under this description are poor crimps, poor solder joints, crimping over wire insulation rather than the wire itself, corrosion in the wire-to-terminal contact area, etc.
^ Wire insulation which is rubbed through, causing an intermittent short as the bare area touches other wiring or parts of the vehicle.
^ Wiring broken inside the insulation. This condition could cause a continuity check or voltage check to show a good circuit, but if only 1 or 2 strands of a multi-strand-type wire are intact, the system may not operate properly.
To avoid any of the above problems when making wiring or terminal repairs, always follow the instructions.
Most antilock brake system failures disable antilock function for the entire ignition cycle, even when the fault clears before key-off. However, some intermittent failure conditions do allow ABS operation to resume when the fault clears before key off.
The following conditions can result in intermittent operation of the amber "ANTILOCK" indicator. Circuits involving these inputs to the EBCM should be investigated when a complaint of intermittent indicator illumination is encountered.
Important
^ When vehicle is equipped with traction control, any symptom which lights the "ANTILOCK" indicator also lights the "TRACTION OFF" indicator. Therefore, when both indicators are lit, follow "ANTILOCK" indicator diagnosis when no diagnostic trouble codes are set.
^ Low System Voltage
When low system voltage is detected by the EBCM, it turns on the amber "ANTILOCK" indicator until normal system voltage is achieved. Once normal voltage is seen at the EBCM, normal operation resumes.
^ Low Brake Fluid in the Pressure Modulator Valve (PMV) Assembly Reservoir
A low brake fluid condition causes the EBCM to illuminate the amber "ANTILOCK" indicator. When the fluid level sensor again indicates an acceptable PMV reservoir fluid level, normal operation resumes.
^ Wheel Speed Sensor Circuitry
Additionally, any condition which results in interruption of power to the EBCM or hydraulic unit may cause the indicator to illuminate intermittently. These circuits include the main relay, pump motor relay and fuses, and related wiring.
Important
Vehicles equipped with traction control contain a prevent system to avoid brake overheating. During heavy braking conditions, if a traction control mode is entered and the EBCM determines the brakes are too hot, the EBCM disables the traction control system and lights only the "TRACTION OFF" indicator. After a sufficient cooling time, approximately 15-20 minutes, the EBCM enables the traction control system and turns off the indicator. This condition is normal and should not be mistaken as an intermittent system malfunction.