Intermittent Malfunction Indicator Light

WARNING: This page is about a different car, the 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

The following conditions may cause intermittent MIL operation with no DTCs stored:

A defective relay, control module driven solenoid, or a switch that causes electrical system interference. Usually the symptom will occur when the faulty component is operating.
The improper installation of add-on electrical devices. These can include lighting systems, 2-way radios and electrical motors.
Ignition Control (IC) wires routed near the generator or secondary ignition system wires and components.
The ignition system secondary voltage shorted to ground.
Poor control or ignition module grounds.
The MIL control circuit intermittently shorted to ground.