Intermittent Problem Diagnosis

Most intermittent problems are caused by faulty electrical connection or wiring. Ensure connector halves and terminals are fully seated and not backed out. Ensure terminals are not damaged an are properly formed, and there is a firm terminal-to-wire connection.

DO NOT use Diagnostic Trouble Code (DTC) procedures to diagnose intermittent problems. Intermittent fault testing requires duplicating circuit or component failure to identify problem. These procedures may result in computer setting a fault code (on some systems) which may help in diagnosis.

If problem vehicle does not produce fault codes, road test vehicle and monitor voltage or resistance values using a DVOM or scan tool. While attempting to reproduce conditions causing intermittent fault, a status change on DVOM or scan tool indicates a fault has been located.

Use a DVOM or scan tool to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position, or engine is running. Ensure ignition switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM or scan tool during test procedures indicate area or component of fault.

An intermittent MIL and no DTCs may be caused by electrical system interference from a defective relay, a PCM-driven solenoid or a switch. These defective components can cause a sharp electrical surge during system operation. Improper installation of add-on electrical options (such as lights and radios), improper routing of ignition wires too close to spark plugs, ignition components and generator can also cause an intermittent MIL.