- Intermittent Malfunctions

DEFINITION
Malfunction may or may not light the Malfunction Indicator Lamp (MIL), or store a Diagnostic Trouble Code (DTC).

PRELIMINARY CHECKS
Perform the careful "Visual And Physical Checks" in Preliminary Checks. - Important Preliminary Checks

DIAGNOSTIC TROUBLE CODE CHARTS
DO NOT use the Diagnostic Trouble Code (DTC) charts for intermittent problems. The fault must be present to locate the problem. If a fault is intermittent, use of DTC charts may result in replacement of good parts.

FAULTY ELECTRICAL CONNECTIONS OR WIRING
Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful check of suspect circuits for:
- Poor mating of the connector halves, or terminals not fully seated in the connector body (backed out).
- Improperly formed or damaged terminals. All connector terminals in problem circuit should be carefully reformed or replaced to ensure proper contact tension.
- Poor terminal to wire connection.

ROAD TEST
If a visual/physical check does not find the cause of the problem, the vehicle can be driven with a digital multimeter or Tech 1 scan tool connected to a suspected circuit. An abnormal reading, when the problem occurs, indicates the problem may be in that circuit. If the wiring and connectors check OK, and a DTC was stored, refer to the On-Board Diagnostic System Check.

INTERMITTENT MALFUNCTION INDICATOR LAMP
An intermittent MIL, and NO DTCs, may be caused by:
- Electrical system interference caused by a defective relay, ECM driven solenoid, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the faulty component is operated.
- Improper installation of electrical options, such as lights, 2-way radios, etc.
- Electronic Spark Advance (ESA) wires should be routed away from spark plug wires, ignition system components and generator.
- Ignition secondary wires shorted to ground.
- MIL PPL/YEL wire for intermittent short to ground.
- ECM power and grounds.

LOSS OF DTC MEMORY
To check, disconnect Engine Coolant Temperature (ECT) sensor connector and idle engine until MIL lights. DTC 14 should be stored, and kept in memory when the ignition switch is turned to the "LOCK" position for at least 10 seconds.
- Check TAIL DOME Fuse.
- Check circuit for open or short to ground.
If OK, the ECM is faulty.