Symptoms - Engine Controls: Intermittent

Important:  Inspect 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 2 circuit. If you can not locate an 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 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 inspection for the following conditions:

• Poor mating of the connector halves or a terminal not fully seated in the connector body backed out
• An improperly formed or damaged terminal
• Reform or replace connector terminals in the problem circuit in order to insure proper contact tension. Refer to CONNECTOR REPAIRS in Wiring Systems.
• Remove the terminal from the connector body in order to inspect for poor terminal to wire connection. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

Road test the vehicle with the DMM connected to the suspected circuit. An abnormal voltage when the malfunction occurs is a good indication of a malfunction in the monitored circuit.

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 tool Freeze Frame/Failure Records can also aid in locating an intermittent condition. Review and capture the information in the Freeze Frame/Failure Record associated with the intermittent DTC being diagnosed. Drive the vehicle in the conditions that were present when the DTC originally set.
• You can use the Plot Function on the scan tool in order to plot selected data parameters. You can then review this stored information. This may aid in locating an intermittent problem. Refer to the scan tool Users Guide for more information.

Important:  If the intermittent condition exists as a start and then stall, inspect for DTCs relating to the vehicle theft deterrent system. Inspect 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 shorted to a 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 condition:

• 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 and Stalling 
• Dieseling, Run-On 
• Backfire