Road Test

If a visual/physical inspection does not locate the cause of the problem, drive the vehicle with a DMM connected to a suspected circuit or use a scan tool. An abnormal voltage or scan reading, when the problem occurs, indicates the problem may be in that circuit.

Intermittent Malfunction Indicator Lamp (MIL)
The following can cause an intermittent MIL and no DTCs:
^ Electrical system interference caused by a malfunctioning relay, ECM driven solenoid, or switch. The electrical component can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
^ The improper installation of electrical devices; such as lights, 2-way radios, electric motors, etc.
^ The MIL circuit intermittently shorted to ground.
^ Poor ECM grounds

Loss of DTC Memory
Inspect for loss of DTC memory by disconnecting the engine coolant temperature (ECT) sensor and idling the engine until the MIL turns ON. An ECT DTC should store and remain in memory when turning OFF the ignition for at least 10 seconds. If not, the ECM is malfunctioning.

Additional Inspection
Inspect for an open diode across the A/C compressor clutch and for other open diodes.