- Intermittent Malfunctions

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

PRELIMINARY CHECKS
Perform the "Visual and Physical Checks" as described in Preliminary Checks. Testing and Inspection

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

FAULTY ELECTRICAL CONNECTIONS OR WIRING
Most intermittent malfunctions 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 malfunctioning circuits 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 malfunction, the vehicle can be driven with a digital multimeter or Tech 1 scan tool connected to a suspected circuit. An abnormal voltage reading, when the malfunction occurs, indicates the malfunction may be in that circuit. If the wiring and connectors check OK and a DTC was stored, refer to the Diagnostic System Check. Testing and Inspection

INTERMITTENT MALFUNCTION INDICATOR LAMP
An intermittent Malfunction Indicator Lamp (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 malfunction 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 an intermittent short to ground.
- Engine Control Module (ECM) power and grounds.

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