- Intermittent Malfunctions

DEFINITION
Problem may or may not turn "ON" the Malfunction Indicator Lamp (MIL) or store a Diagnostic Trouble Code (DTC).

PRELIMINARY CHECKS
^ Refer to Important Preliminary Checks. - Important Preliminary Checks
^ DO NOT use the DTC charts for intermittent problems. The fault must be present to locate the problem. If a fault is intermittent, use of diagnostic trouble code 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 insure proper contact tension.
- Poor terminal to wire connection. This requires removing the terminal from the connector body to check. Refer to Vehicle On-Board Diagnosis. Testing and Inspection

ROAD TEST
^ If a visual/physical check does not locate the cause of the problem, the vehicle can be driven with a voltmeter connected to a suspected circuit or a Tech 1 scan tool may be used. An abnormal voltage or scan reading, when the problem occurs, indicates the problem may be in that circuit. If the wiring and connectors check OK, and a diagnostic trouble code was stored for a circuit having a sensor, replace the sensor.

INTERMITTENT "MALFUNCTION INDICATOR LAMP (MIL)"
^ An intermittent MIL and No Diagnostic Trouble Codes (DTCs), may be caused by:
- Electrical system interference caused by a defective relay, control module 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 devices, such as lights, 2-way radios, electric motors, etc.
- Ignition secondary shorted to ground.
- CKT 419 Malfunction Indicator Lamp (MIL) or CKT 451 (diagnostic "test" terminal) intermittently shorted to ground.
- Control module grounds. Refer to Connector Views/Diagrams. Connector Views

LOSS OF DIAGNOSTIC TROUBLE CODE MEMORY
^ To check, disconnect Engine Coolant Temperature (ECT) sensor and idle engine until the "Malfunction Indicator Lamp comes ON." DTC 15 should be stored, and kept in memory when the ignition is turned "OFF" for at least 10 seconds. If not, the control module is faulty.