Possible Causes & Corrections
Use following procedures to determine possible causes of intermittent Malfunction Indicator Light (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 wire from Malfunction Indicator Light (MIL) to PCM for short to ground.
- Check wire from Data Link Connector (DLC) test terminal for intermittent short to ground.
- 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 is operated.
- Check for aftermarket parts which may not have been produced to manufacturers' 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 overvoltage (over 16 volts on most models). PCM repowers when condition ceases to exist. A rapid shutdown and repower could cause a flickering Malfunction Indicator Light (MIL) with no codes set in memory.
- Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
- Ensure EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and generator. Ensure ground wire from PCM to distributor or ignition module is connected to a good ground.
- Check for intermittent short to ground on terminal "B" (diagnostic enable) of Data Link Connector (DLC) or in Malfunction Indicator Light (MIL) circuit.
- On vehicles not equipped with a driver information center, use scan tester to check for intermittent wiring problem. See SCAN TESTER USAGE in the TESTS W/CODES article.