GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L 🢒 Intermittent Conditions

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). Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs and Wiring Repairs .
    •  Improperly formed or damaged terminal. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs and Wiring Repairs .
    •  All connector terminals in the problem circuit should be carefully checked for proper contact tension. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs and Wiring Repairs .
    •  Poor terminal to wire connection. This requires removing the terminal from the connector body to check. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs and Wiring Repairs .

Road test the vehicle with a J 39200 Digital Multimeter (DMM) 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. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs and Wiring Repairs .
    •  Poor PCM grounds, refer to Power and Grounding Components .

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.