- Intermittent Malfunctions

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

PRELIMINARY CHECKS
^ Refer to IMPORTANT PRELIMINARY CHECKS.
Testing and Inspection
^ DO NOT use the Diagnostic Trouble Code (DTC) 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.

FAULTY ELECTRICAL CONNECTIONS OR WIRING
^ Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful check of suspect 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 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.

ROAD TEST
^ If a visual/physical check does not locate the cause of the problem, the vehicle can be driven with J 39200 voltmeter connected to a suspected circuit or a TECH 1 scan tool may be used. 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 DTCs 44 and 45, replace the sensor.
^ The TECH 1 scan tool has the ability to manually or automatically record sensor and data values in the "Snapshot" mode. This feature allows viewing of data values over a time period before and after the Diagnostic Trouble Code (DTC) or disturbance occurs.

INTERMITTENT "MALFUNCTION INDICATOR LAMP (MIL)"
^ An intermittent MIL and no Diagnostic Trouble Codes (DTCs), may be caused by:
- Electrical system interference caused by a defective relay, control module 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 devices, such as lights, 2-way radios, electric motors, etc.
- Ignition Control (IC) wires should be routed away from spark plug wires, ignition system components and generator. Wire for CKT 453 from control module to ignition system should be a good ground.
- Ignition secondary shorted to ground.
- CKT 419 Malfunction Indicator Lamp (MIL) or CKT 451 (diagnostic "test" terminal) intermittently shorted to ground.
- Control module grounds.

LOSS OF DIAGNOSTIC TROUBLE CODE MEMORY
^ To check, disconnect Throttle Position (TP) sensor and idle engine until the "Malfunction Indicator Lamp" comes "ON." DTC 22 should be stored, and kept in memory when the ignition is turned "OFF" for at least 10 seconds. If not, the control module is faulty.

QUITS WHILE DRIVING
^ Check for a failed injector driver in control module. If the injector driver fails, the oxygen sensor will sense a lean fuel mixture and display a steady low voltage (about 0 mV) on a scan tool. The control module will also command a higher injector base pulse width (about 20 Ms). This problem can be diagnosed by monitoring the oxygen sensor and injector base pulse width with a TECH 1 scan tool while backprobing the control module injector driver circuit at the control module with J 39200 DVOM. At the point when vehicle fails, the J 39200 will not display frequency on injector driver coming from the control module. If injector driver fails, replace the control module.

ADDITIONAL CHECKS
^ Check for open diode across A/C compressor clutch, and for other open diodes. Refer ENGINE CONTROL MODULE/DIAGRAMS/ELECTRICAL/ECM/PCM WIRING DIAGRAMS.
Diagrams