Intermittent Conditions

IMPORTANT: A problem may or may not turn on the 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.

Most intermittent problems are caused by faulty electrical connections or wiring. Perform careful visual/physical inspections and tests for the following conditions:
^ An incorrect mating of the connector halves or a terminal not fully seated in the connector (backed out).
^ An incorrectly formed terminal or a damaged terminal.
^ All of the connector terminals in the faulty circuit should be carefully tested for the correct contact tension.
^ A faulty terminal to wire connection. This may require removing the terminal from the connector body in order to inspect the connection.

The vehicle may need to be driven with a DMM connected to the suspected circuit. An abnormal voltage is a good indication that there is a malfunction in the circuit being monitored.

A scan tool can be used to help detect intermittent conditions. The scan tool has several features that can be used to locate an intermittent condition.

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 tool's Freeze Frame buffer can also aid in locating an intermittent condition. Review and record the information in the Freeze Frame associated with the intermittent DTC being diagnosed. The vehicle can be driven within the conditions that were present when the DTC originally set.

To test for loss of DTC memory, disconnect the Throttle Position (TP) sensor and idle the engine until the MIL illuminates. DTC P0122 should be stored and kept in memory when the ignition is turned off. If the DTC is not stored, the PCM is faulty. When this test is complete, make sure that you clear the DTC P0122 from memory.

An intermittent MIL with no stored DTC may be caused by the following concerns:
^ An ignition coil shorted to ground and arcing at the ignition wires or at the spark plugs.
^ An MIL wire to the PCM shorted to ground.
^ Any faulty PCM grounds

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

Test for an electrical system interference caused by the following components:
^ A malfunctioning relay
^ A PCM driven solenoid
^ A switch

The above components can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operated.

Inspect for improper installation of electrical options such as lights, cellular phones, etc.

All of the Ignition Control Module (ICM) wiring should be routed away from the generator. Inspect all of the wires from the PCM to the ICM for faulty connections.

Test for an open diode across the A/C compressor clutch, or other open diodes.