- Intermittent Malfunctions

Note: Problem may or may not turn "ON" the "Service Engine Soon" light, or store a code.

The ECM code charts, determine if there is a fault with a circuit, or, if there is an intermittent problem. The fault must be present to locate the problem. If a fault is intermittent, use of Trouble Code Charts may result in replacement of good parts. An intermittent means that a code is stored in the ECM memory, but the circuit is OK.
Refer to wiring diagrams.

- Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful check of the suspected 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 a problem circuit, should be carefully reformed to increase contact tension.
- Poor terminal to wire connection. This requires removing the terminal from the connector body.
- 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 or a "Scan" tool may be used. An abnormal voltage 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 44 and 45, substitute a known good sensor and recheck.
- Loss of code memory: To check, disconnect 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," for at least 10 seconds. If not, check for open in CKT 440 (Fuel Pump Circuit of ECM) to the ECM. If CKT 440 has 12 volts to the ECM at all times, replace ECM.
- CHECK:
- 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.
- Improper installation of electrical options, such as lights, 2-way radios, etc.
- EST wires should be routed away from spark plug wires, distributor wires, distributor housing, coil, and generator. Wire from CKT 453 (Ignition Circuit of ECM) to distributor should have a good contact to ground.
- Ignition secondary shorted to ground.
- CKTs 419 (SES light) and 451 (Diagnostic Test) intermittently shorted to ground.
- ECM power grounds.
- Incorrect or defective Cal-Pak / PROM.