- Intermittent Malfunctions

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

CAUTION: DO NOT use the diagnostic trouble code 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.

^ Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful visual/physical check.
Check for:
- Poor mating of the connector halves or terminal not fully seated in the connector body (backed out).
- Improperly formed or damaged terminal. All connector terminals in the problem circuit should be carefully replaced to ensure proper contact tension.
- 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 I scan tool can also be used to help detect intermittent conditions. 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, except for DTC P0131, P0132, P0134, substitute a known good sensor and recheck.
^ Loss of diagnostic code memory. To check, disconnect Throttle Position (TP) sensor and idle engine until MIL comes "ON." DTC P0122 should be stored, and kept in memory when ignition is turned "OFF." If not, the Powertrain Control Module (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 plug wires or plugs.
- MIL (Service Engine Soon) wire to PCM shorted to ground (CKT 419).
- PCM grounds.
^ 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, car phones, CB antenna lead near PCM harness causing false readings and DTCs, etc.
^ Check for open diode across A/C compressor clutch, located in the harness approximately 10 - 15 inches from the A/C compressor, and for other open diodes (refer to wiring diagrams).
^ If problem has not been found, refer to PCM Connector Symptom charts. Pinout Values and Diagnostic Parameters