- Intermittent Malfunctions

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

PRELIMINARY CHECKS
^ Refer to Diagnostic Notes. Initial Inspection and Diagnostic Overview
^ 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.

ROAD TEST
^ If a visual/physical check does not locate the cause of the problem, the vehicle can be driven with J 39200 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 DTC was stored for a circuit having a sensor, except for DTCs 44 and 45, replace the sensor.

INTERMITTENT MALFUNCTION INDICATOR LAMP (MIL)
^ An intermittent MIL and No 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 Control (IC) wires should be routed away from spark plug wires, ignition system components and generator. Wire for CKT 453 from control module to ignition system should be a good ground.
- Ignition secondary shorted to ground.
- CKT 419 MIL or CKT 451 (diagnostic "test" terminal) intermittently shorted to ground.
- Control module grounds.

LOSS OF DIAGNOSTIC TROUBLE CODE MEMORY
^ To check, disconnect Throttle Position (TP) sensor and idle engine until the MIL comes "ON." DTC 22 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.