GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC P42 Commercial Chassis 🢒 Engine 🢒 Engine Controls - 6.5L (L57) 🢒 Intermittent Conditions

Checks

Action

Definition: The problem may or may not turn the Malfunction Indicator Lamp (MIL) or store a Diagnostic Trouble Code (DTC).

Preliminary Checks
    • Refer to Symptoms .
    • The fault must be present to locate the problem. If a fault is intermittent, the use of DTC Tables may result in the replacement of good parts.

Electrical Connections or Wiring

Poor electrical connections or wiring can cause most intermittent problems. Perform a careful check of the suspected circuit for the following:

    • Check for poor mating of the connector halves, or terminals not fully seated in the connector body (backed-out).
    • Check for improperly formed or damaged terminals. Carefully reform or replace all the connector terminals in the problem circuit to ensure the proper contact tension.
    • Check for poor terminal to wire connections. This requires removing the terminal from the connector body to check.

Road Test

If a visual/physical check does not locate the cause of the problem, drive the vehicle with a J 39200 connected to a suspected circuit or use a scan tool. An abnormal voltage or scan reading, when the problem occurs, indicates the problem may be in that circuit.

Intermittent Malfunction Indicator Lamp (MIL)

The following can cause an intermittent MIL and no DTCs:

    • Electrical system interference caused by a malfunctioning relay, PCM driven solenoid or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
    • The improper installation of electrical devices; such as lights, 2-way radios, electric motors, etc.
    • The Malfunction Indicator Lamp (MIL) circuit intermittently shorted to ground.
    • Poor PCM grounds.

Loss of DTC Memory

Check for loss of DTC memory by disconnecting the Engine Coolant Temperature (ECT) sensor and idling the engine until the MIL turns ON. An Engine Coolant Temperature (ECT) DTC should store and remain in memory when turning OFF the ignition for at least 10 seconds. If not, the PCM is malfunctioning.

Additional Checks

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