- Intermittent Malfunctions

Important: Check for improper installation of electrical components if an intermittent condition exists. Inspect for aftermarket theft deterrent devices, lights and cellular phones. Ensure that no aftermarket equipment is connected to the Class II circuit. If you can not locate the intermittent condition, a cellular phone signal communication may cause the condition.

Important: The problem may or may not turn on the Malfunction Indicator Lamp (MIL) or store a DTC. DO NOT use the Diagnostic Trouble Code (DTC) tables for intermittent problems. The fault must be present in order to locate the problem.

Faulty electrical connections or wiring cause most intermittent problems. Perform a careful visual/physical check for the following conditions:

^ Poor mating of the connector halves or a terminal not fully seated in the connector body (backed out).

^ Improperly formed or damaged terminal.

^ Reform or replace connector terminals in the problem circuit in order to insure proper contact tension.

^ Poor terminal to wire connection requires removing the terminal from the connector body in order to check.

Road test the vehicle with a Digital Multimeter (DMM) J 39200 connected to the suspected circuit. An abnormal voltage when the malfunction occurs is a good indication that there is a malfunction in the circuit being monitored.

Use a scan tool in order to help detect intermittent conditions. The GM Techline equipment (Scan Tool) has several features that you can use to locate an intermittent condition. Use the following features to find intermittent faults:

^ You can trigger the Snapshot feature in order to capture and store engine parameters within the scan tool when the malfunction occurs. You can then review this stored information in order to see what caused the malfunction.

^ Using a Scan Tools Freeze Frame buffer or Failure Records buffer can also aid in locating an intermittent condition. Review and capture the information in the Freeze Frame and/or Failure record associated with the intermittent DTC being diagnosed. Drive the vehicle in the conditions that were present when the DTC originally set.

Important: If the intermittent condition exists as a start and then stall, check for DTCs relating to the theft deterrent system. Check for improper installation of electrical options such as lights, cellular phones etc.

Any of the following may cause an intermittent Malfunction Indicator Lamp (MIL) with no stored DTC:

^ The ignition coils for being shorted to ground, arcing at the ignition wires or the spark plugs.

^ The PCM grounds, refer to Engine Controls Schematics.

^ The Ignition Control (IC) wires for being routed to close to the secondary ignition wires, coils, or the generator - Ensure that all of the circuits from the PCM to the ignition coils have good connections.

^ An open diode across the A/C compressor clutch and other open diodes.

Use the following tables when diagnosing a symptom complaint.

^ Hard Start.

^ Surges/Chuggles.

^ Lack of Power, Sluggishness, or Sponginess.

^ Detonation/Spark Knock.

^ Hesitation, Sag, Stumble.

^ Cuts Out, Misses.

^ Poor Fuel Economy.

^ Rough, Unstable, or Incorrect Idle, Stalling.

^ Dieseling, Run-On.

^ Backfire.


Intermittent Condition

A problem may or may not turn ON the Malfunction Indicator Lamp (MIL) or store a DTC. DO NOT use the Diagnostic Trouble Code (DTC) charts for intermittent problems. The fault must be present to locate the problem.

Most intermittent problems are caused by faulty electrical connections or wiring. Perform a careful visual/physical check for the following conditions:

^ Poor mating of the connector halves or a terminal not fully seated in the connector (backed out).

^ Improperly formed or damaged terminal.

^ All connector terminals in the problem circuit should be carefully checked for proper contact tension.

^ Poor terminal to wire connection. This requires removing the terminal from the connector body to check.

Road test the vehicle with a J 39200 Digital Multimeter connected to a suspected circuit. An abnormal voltage when malfunction occurs is a good indication that there is a fault in the circuit being monitored.

Use a scan tool to help detect intermittent conditions. The scan tool has several features that can be used to locate an intermittent condition. Use the following features to find intermittent faults:

^ The Snapshot feature can be triggered to capture and store engine parameters within the scan tool when the malfunction occurs. This stored information then can be reviewed by the service technician to see what caused the malfunction.

^ Using a Scan Tools Freeze Frame data or Failure Records data can also aid in locating an intermittent condition. Review and record the information in the freeze frame or failure record associated with the intermittent DTC being diagnosed. The vehicle can be driven within the conditions that were present when the DTC originally set.

An intermittent MIL (Service Engine Soon) with no stored DTC may be caused by the following:

^ Ignition coil shorted to ground and arcing at ignition wires or plugs.

^ MIL (Service Engine Soon) wire to PCM shorted to ground.

^ Poor PCM grounds, refer to PCM wiring diagrams.

Check for improper installation of electrical options such as lights, cellular phones etc. Route Ignition Control (IC) Module wiring away from secondary ignition wires and ignition coils. Check all wires from the PCM to the ignition control module for poor connections.