Intermittent Symptoms
SYMPTOM DESCRIPTION:Problems may or may not turn "CHECK ENGINE" light "ON" 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 connector halves or terminals not fully seated in 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. Requires removing terminal from connector body to check.
ROAD TEST
If a visual/physical check does not locate the problem, 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 wiring and connectors check OK, and a fault code was stored for a circuit having a sensor, replace suspect sensor. If an abnormal voltage reading is detected, wiring and connectors are OK and no codes were set, ECU or power supply may be defective.
NOTE: Make note of any codes stored and clear ECU 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 codes could be caused by:
^ Low battery voltage
^ Intermittent grounding of "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, problem will occur when faulty component is operated.
^ Improper installation of electrical devices, such as lights, mobile phones, 2-way radios, electric motors....etc.
^ ECU grounds.
LOSS OF FAULT CODE MEMORY
Loss of fault code memory may be caused by:
^ Low battery voltage
^ Loss of power to ECU
^ Defective ECU