Possible Causes & Corrections

Use the following procedures to determine possible causes of intermittent MIL operation:

• Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire-to-terminal connections.
• Check for poor connection from ignition coil to ground or arcing at spark plug wires or plugs.
• Check for poor connections in PCM ground terminals.
• Check for electrical system interference caused by defective relay, PCM-driven solenoid or switch, which may cause sharp electrical surge. This type of problem will normally occur when faulty component are operated.
• Check for aftermarket parts which may not have been produced to manufacturer's specifications. Check for solenoids or relays without original equipment diodes for circuit protection.
• Check for improper installation of electrical accessories such as theft deterrent devices, auxiliary lights, cellular phone etc.
• Ensure Ignition Control (IC) module wiring is kept away from spark plug wires, ignition coil and generator. Ensure ground wire from PCM to IC module is connected to a good ground.
• Check for intermittent short to ground on data circuits of Data Link Connector (DLC) or in MIL circuit. See WIRING DIAGRAMS article.
• On vehicles not equipped with a driver information center, use scan tool to check for intermittent wiring problem. See SCAN TOOL USAGE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.