Diagnostic Strategies

As with most any electronic system, intermittent failures are difficult to accurately diagnose. The diagnostic trouble codes stored by the EBCM/EBTCM 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 intermittent condition is being diagnosed, use the EBCM/EBTCM'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/EBTCM.

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 to identify and isolate suspect circuits. Diagnostic Trouble Code (DTC) Guide

^ When no diagnostic trouble codes are stored, it becomes necessary to use symptom diagnosis. Diagnostic Symptom Guide

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 is also useful in isolating the failure. Diagnostic Symptom Guide

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 for the specific procedure. Checking Terminal Contact

^ The J 25616-1 Connector Test Adapter Kit must be used whenever a diagnostic procedure requires checking or probing a terminal. Using the adapter ensures that no damage to the terminal occurs and that contact tension is sufficient. If contact tension seems insufficient, refer to Checking Terminal Contact for specifics. Checking Terminal Contact

^ Poor terminal-to-wire connection. Checking this requires removing the terminal from the connector body, as outlined in Repairing Connectors." 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 Repair Procedures

^ 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; however, 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 for wiring and terminal repair. Wire Repair Procedures

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/EBTCM should be investigated when a complaint of intermittent indicator illumination is encountered.

NOTE: 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/EBTCM, it turns on the amber ANTILOCK indicator until normal system voltage is achieved. Once normal voltage is seen at the EBCM/EBTCM, normal operation resumes.

^ Low Brake Fluid in the Pressure Modulator Valve (PMV) Assembly Reservoir.

A low brake fluid condition causes the EBCM/EBTCM to illuminate the amber ANTILOCK indicator. When the fluid level switch 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/EBTCM or hydraulic unit may cause the indicator to illuminate intermittently. These circuits include the main relay, ABS pump relay and fuses, and related wiring.

NOTE:

^ 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/EBTCM determines the brakes are too hot, the EBCM/EBTCM disables the traction control system and lights only the TRACTION OFF indicator. After a sufficient cooling time, approximately 15-20 minutes, the EBCM/EBTCM enables the traction control system and turns off the indicator. This condition is normal and should not be mistaken as an intermittent system malfunction.

Checking Terminal Contact
When diagnosing an electrical system that uses Metri-Pack 150/280/480/630 series terminals (refer to Terminal Repair Kit J 38125-A instruction manual and J 38125-4 for terminal identification), it is important to check terminal contact between a connector and component, or between in-line connectors, before replacing a suspect component.

Frequently, a diagnostic chart leads to a step that reads "Check for proper connection..." Mating terminals must be inspected to ensure good terminal contact. A poor connection between the male and female terminal at a connector may be the result of contamination or deformation.

Contamination is caused by the connector halves being improperly connected; a missing or damaged connector seal; or damage to the connector itself, exposing the terminals to moisture and dirt. Contamination, usually in underhood or underbody connectors, leads to terminal corrosion, causing an open circuit or an intermittently open circuit.

Deformation is caused by probing the mating side of a connector terminal without the proper adapter, improperly joining the connector halves, or repeatedly separating and joining the connector halves. Deformation, usually to the female terminal contact tang, can result in poor terminal contact, causing an open or intermittently open circuit. Refer to "Repair Procedures".