- Intermittent Malfunctions

Problem may or may not turn ON the MIL (Malfunction Indicator Lamp) or store a DTC. DO NOT use the Diagnostic Trouble Code (DTC) tables 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 body (backed out).

^ Improperly formed or damaged terminal.

^ All connector terminals in the 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 the vehicle with a J 39200 Digital Multimeter connected to a 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 to help detect intermittent conditions. The GM Techline equipment (Scan Tool) have 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 buffer or Failure Records buffer can also aid in locating an intermittent condition. Review and capture the information in the freeze frame or failure record associated with the intermittent DTC being diagnosed. The vehicle can be driven in the conditions that were present when the DTC originally set.

Loss of diagnostic code memory. To check, disconnect MAP sensor and idle engine until the MIL (Malfunction Indicator Lamp) comes ON (The engine speed may require to be increased to 2000 RPM). DTC P0107 should be stored and kept in memory when ignition is turned OFF. If not the PCM is faulty. When this test is completed, DTC P0107 should be cleared from memory.

An intermittent MIL (Malfunction Indicator Lamp) with no stored DTC may be caused by the following:

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

^ PCM grounds, refer to PCM wiring diagrams. If the intermittent condition exists as a start and then stall, check for DTC(s) relating to the theft deterrent system. Check for improper installation of electrical options such as lights, cellular phones etc.

All Ignition Control (IC) wires should be routed away from secondary ignition wires, distributor, coil, and generator. All wires from the PCM to distributor should have a good connection.

Check for open diode across A/C compressor clutch and for other open diodes.