- Intermittent Malfunctions

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

PRELIMINARY CHECKS
Perform the careful visual and physical checks as described in Preliminary Checks. Testing and Inspection

DIAGNOSTIC TROUBLE CODE CHARTS
DO NOT use the DTC charts for intermittent problems. 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.

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. Refer to Diagrams/Diagnostic Aids/Connector Repair. Diagrams

ROAD TEST
If a visual/physical check does not find the cause of the problem, the vehicle can be driven with a digital multimeter (J39200) connected to a suspected circuit or a Tech 1 scanner may be used. An abnormal voltage or scan reading, when the problem occurs indicates the problem may be in that circuit.

INTERMITTENT MIL
An intermittent MIL, and no DTCs may be caused by:

^ Electrical system interference caused by a defective relay, Engine Control Module (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.

^ IC wires should be routed away from ignition wires, ignition system components, and generator. Wire for CKT 453 from ECM to ignition system should be a good ground.

^ Ignition secondary shorted to ground.

^ CKT 419 MIL or CKT 451 (Diagnostic "Test" Terminal) intermittently shorted to ground.

^ ECM power grounds.

LOSS OF DIAGNOSTIC TROUBLE CODE MEMORY
To check, disconnect Manifold Absolute Pressure (MAP) sensor and idle engine until MIL comes "ON." DTC 34 should be stored, and kept in memory when the ignition is turned "OFF" for at least 10 seconds. If not, the ECM is faulty.