Intermittents

Definition: Problem may or may not turn "ON" the "Check Engine" malfunction indicator lamp or store Diagnostic Trouble Code (DTC).

DO NOT use the DTC Trouble Code Charts for an intermittent problem. The fault must be present to locate the problem. If a fault is intermittent, use of DTC charts may result in replacement of good parts.


Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful visual/physical check as described at start of "Symptoms,". 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 reformed or replaced to insure 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 car can be driven with a voltmeter connected to a suspected circuit. A "Scan tool" can also be used to help detect intermittent conditions. An abnormal voltage, or "Scan" tool 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 DTC(s) 44 and 45, substitute a known good sensor and recheck.

- Loss of DTC memory. To check, disconnect throttle position (TP) sensor and idle engine until "Check Engine" malfunction indicator lamp comes "ON". DTC 21 should be stored, and kept in memory when ignition is turned "OFF". If not, the Engine Control Module (ECM) is faulty.

- An intermittent "Check Engine" malfunction indicator lamp with no stored DTC may be caused by:

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

- "Check Engine" malfunction indicator lamp wire to ECM shorted to ground.

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

- ECM grounds, refer to ECM wiring diagrams.

- 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.

- Ignition control wires should be routed away from spark plug wires, electronic ignition (EI) wires, EI housing, coil and generator. Ground wire from ECM to EI should have a good connection.

- If problem has not been found, refer to "ECM Connector Symptom" charts at the end of "symptoms,".