Possible Causes & Corrections

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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 problem component is operated.
Check for aftermarket parts which may not have been produced to manufacturer's specifications. Solenoids without original equipment diodes for circuit protection or voltage regulator using transistors instead of silicone-chip circuitry may cause voltage surges (up to 300 volts) in PCM wiring, causing temporary PCM shutdown. PCM shutdown is a normal response to system over voltage (over 16 volts on most models). PCM re-powers when condition ceases to exist. A rapid shutdown and re-power could cause a flickering MIL with no DTCs set in memory.
Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
Ensure ground wire from PCM to distributor or ignition module is connected to a good ground.
Check for intermittent short to ground on data circuits of DLC or in MIL circuit. See DATA LINK CONNECTORS article in WIRING DIAGRAMS.
On vehicles not equipped with a driver information center, use scan tool to check for intermittent wiring problem. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.