Intermittent "Engine Control System Fault" Telltale

Definition: "Engine Control System Fault" telltale comes on at times, but does not stay on. There may or may not be a stored code.

Intermittent problems with history trouble codes stored can be diagnosed through the Trouble Code Charts. These trouble codes include a "Notes on Intermittents" in the text describing a suggested procedure for isolating the location of intermittent malfunctions. Additionally, all affected circuits should be tested through the use of the
status lights, the switch tests, the output cycling tests,or the ECM/BCM data displays if possible.
^ Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful visual check as described at start of Symptoms. - Visual/Physical Underhood Inspection
Check for:
^ 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 to increase contact tension.
^ Bad terminal to wire connection. This requires removing the terminal from the connector body to check for corrosion, body sealer or other foreign material.
^ If a visual check does not find the cause of the problem, the car can be driven while using parameters or with a voltmeter connected to the suspected circuit and ground. If the voltage reading changes as the problem occurs, the problem is in that circuit.
^ Check for intermittent connection in circuit from:
^ ignition coil secondary to ground and look for arcing at spark plug wires or plugs.
^ Check for loose battery power connections at the battery, jump start junction block, generator output terminal, battery to starter solenoid and starter solenoid to starter.
^ Check for loose or improperly connected ground to rear junction block (circuit 1030).
^ "Engine Control System Fault" telltale wire to ECM for short to ground.
^ ECM terminals A12 and D1 to engine ground.
^ Loss of trouble code memory. To check, disconnect TPS and idle engine until "Engine Control System" lamp comes on. Code EO22 should be stored, and kept in memory when ignition is turned off. If not, the ECM is faulty.
^ Check for an electrical system interference caused by a defective relay, ECM driven solenoid, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the faulty component is operated.
^ Check the vehicle's main power and ground connections.
^ Check for non-original equipment (OE) or non-OE equivalent ignition parts such as ignition coils, distributor caps, distributor rotors, and spark plug wires. Some after market equipment may not meet GM specifications for transient suppression. Replace any suspect parts with OE or known good equivalent before proceeding with diagnoses.
^ EST wires should be kept away from spark plug wires, distributor wires, distributor housing, ignition coil, and generator. Wire from ECM C/D connector (terminal D9-circuit 453) to distributor, should provide the ECM and distributor with a good common ground. The shield and drain wire provided for circuits 430 distributor reference and 453 EST ground should be intact. The Distributor Reference circuit 430, and EST ground circuit 453, will be susceptible to induced transient voltages if not shielded and routed as designed.
^ Check for improper installation of electrical options, such as lights, 2-way radios, etc.