- Intermittent Malfunctions

DESCRIPTION
Intermittent Problems may or may not turn "ON" the "Service Engine Soon" light or store a code. DO NOT use the trouble codes in "A-Charts" for intermittent problems. The fault must be present to locate the problem. If a fault is intermittent, use of trouble code charts may result in wasted time and replacement of good parts.

INSPECTION
Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful check as described in When To Use This Section. - When to Use This Section

Check 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 to increase contact tension.

- Poor terminal to wire connection. This requires removing the terminal from the connector body to check.

If a visual check does not find the cause of the problem, the car can be driven with a voltmeter connected to a suspected circuit. A "Scan" tool can, also, be used for monitoring input signals 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 trouble code was stored for a circuit having a sensor, except for Codes 43, 44 and 45, substitute a known good sensor and recheck.


An intermittent "Service Engine Soon" light with no stored code may be caused by:

- Ignition coil shorted to ground and arcing at spark plug wires or plugs.

- "Service Engine Soon" light wire to Electronic Control Module (ECM) shorted to ground.

- Diagnostic "test" terminal wire to ECM, shorted to ground.

- ECM power grounds. See ECM wiring diagrams.

Loss of trouble code memory
To check, disconnect Throttle Position Sensor (TPS) and idle engine until "Service Engine Soon" light comes "ON." Code 22 should be stored, and kept in memory when ignition is turned "OFF." If not, the ECM is faulty.

Check for an electrical system interference caused by a defective relay, ECM 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.

Electronic Spark Timing (EST) wires should be kept away from spark plug wires, coils and generator. Wire from ECM to ignition system should be a good connection.

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