Intermittent Symptoms

SYMPTOM DESCRIPTION:
Problems may or may not turn "ON" the "CHECK ENGINE" light, or store a code.





FAULTY ELECTRICAL CONNECTIONS OR WIRING

Most intermittent problems are caused by faulty electrical connections or wiring. Perform a careful check of suspect circuits for:

^ Signs of moisture at terminal connectors or relay boxes.
^ Poor mating of the connector halves, or terminals not fully seated in the connector body (backed out).
^ Improperly formed or damaged terminals. All connector terminals in problem circuit should be carefully reformed or replaced to insure proper contact tension.
^ Poor terminal to wire connection. This requires removing the terminal from the connector body to check.



ROAD TEST

If a visual/physical check does not find the cause of the problem, the vehicle can be driven with a voltmeter connected to a suspected circuit. An abnormal voltage reading, when the problem occurs, indicates the problem may be in that circuit. If the wiring and connectors checkout OK, and a trouble code was stored for a circuit having a sensor, replace the suspect sensor. If an abnormal voltage reading is detected, the wiring and connectors being OK, and no codes were set in fault memory, the control unit(s), power supply, or overvoltage relay may be defective.

NOTE: It would be advantageous to note any codes stored and clear the control unit(s) memory prior to road testing. This may eliminate any false codes not related to the complaint.




INTERMITTENT "CHECK ENGINE" LIGHT

An intermittent "CHECK ENGINE" light, and No Diagnostic Codes, could be caused by:

^ Low battery voltage
^ Low engine idle RPM
^ Intermittent grounding of the "CHECK ENGINE" light circuit
^ Poor electrical connections (loose, corroded, moisture)
^ Electrical system interference caused by a defective relay or control unit. These components can cause a sharp electrical surge. Normally the problem will occur when the faulty component is operated.
^ Improper installation of electrical devices, such as lights, mobile phones, 2-way radios, electric motors, etc.
^ Control unit grounds.
Checking the Basics



LOSS OF FAULT CODE MEMORY

Loss of fault code memory may be caused by:

^ Low battery voltage
^ Loss of power to the control unit
^ Defective DME control unit