- Intermittent Malfunctions

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

CAUTION: DO NOT use the "Diagnostic Trouble Code Charts" under "Diagnostic 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 the replacement of good parts.



^ Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful visual/physical check as described in "Preliminary Checks": Testing and Inspection
- Poor mating of the connector halves, or terminals not fully seated in the connector body (backed out).
- Improperly formed or damaged terminal(s). All connector terminals in the problem circuit should be carefully reformed or replaced to ensure proper contact.
- Poor terminal to wire connection. This requires removing the terminal from the connector body to check.

^ If a visual/physical check does not find the cause of the problem, the vehicle can be driven with a voltmeter connected to a suspected circuit. A Tech 1 scan tool can also be used to help detect intermittent conditions. An abnormal voltage, or Tech I scan tool 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, except for DTC(s) 44 and 45, substitute a known good sensor and recheck.

^ Loss of DTC memory. To check, disconnect TP sensor and idle engine until Malfunction Indicator Lamp (MIL) comes "ON." DTC 22 should be stored, and kept in memory when ignition is turned "OFF." If not, the PCM is faulty.

^ An intermittent MIL with no stored diagnostic trouble code may be caused by:
- Ignition coil shorted to ground and arcing at spark plugs.
- MIL wire to PCM shorted to ground (CKT 419).
- Diagnostic "test" terminal wire to PCM, shorted to ground (CKT 448).
- PCM grounds, refer to PCM wiring diagrams.

^ Check for an electrical system interference caused by a defective relay, PCM driven solenoid, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the faulty component is operated.

^ Check for improper installation of electrical options such as lights, 2 way radios, etc.

^ Ignition Control (IC) wires should be routed away from spark plug wires and ignition system components. Generator wire CKT 453 from PCM to ignition system should have a good ground.

^ Check for open diode across A/C compressor clutch, and for other open diodes (refer to wiring diagrams).

^ If problem has not been found, refer to "PCM Connector Symptom" charts in this section. Pinout Values and Diagnostic Parameters