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)
^ Improperly formed or damaged terminal
^ All connector terminals in the problem circuit should be carefully checked for proper contact tension
^ Poor terminal to wire connection

To properly inspect connection, remove the terminal from the connector body.

Road test the vehicle with the 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 the 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

Loss of diagnostic code memory. To check, disconnect the MAP sensor and idle engine until the MIL (Service Engine Soon) comes ON. 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, make sure that you clear the DTC P0107 from memory.

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
^ Poor PCM grounds
Refer to PCM Power and Ground Check (2 of 2) or to PCM Power and Ground Check (1 of 2). Component Tests and General Diagnostics Component Tests and General Diagnostics

Inspect 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. Inspect all wires from the PCM to the ignition control module for poor connections.

Inspect for open diode across A/C compressor clutch and inspect for other open diodes

The following are the Symptom tables:

^ Hard Start
^ Surges/Chuggles
^ Lack of Power, Sluggishness, or Sponginess
^ Detonation/Spark knock
^ Rough, Unstable, or Incorrect Idle and Stalling
^ Poor Fuel Economy
^ Excessive Exhaust Emissions or Odors
^ Dieseling, Run-On
^ Backfire
^ Cuts Out, Misses
^ Hesitation, Sag, Stumble
^ Restricted Exhaust System Check

Most tables have one result which reads FAULT NOT PRESENT. This means that the conditions that were present when the DTC set are no longer there. This does not mean that the problem is fixed, it simply means that the problem is intermittent. The problem was present but is not present now. The problem is likely to return in the future so it should be diagnosed and repaired if at all possible. The only way to diagnose a problem that is not present is to gather information from the time when the DTC was set. This can be done in two ways; through snapshot data and driver observations.

Snapshot data whether Freeze Frame, Failure Records or scan tool snapshot, can be used to check data parameters to see if they fall within normal operating range. For example, a snapshot MAP parameter value of 100 while the engine was idling is not normal and would indicate that the MAP sensor voltage went high either due to an open in the 5 volt return or a short to voltage on the sensor signal circuit. Driver observations may give additional information about the system or area of the car that should be checked for an intermittent. For example, while diagnosing an intermittent DTC P0550, you find out the driver noticed that the SERVICE VEHICLE SOON message only comes on after an extended Wide Open Throttle maneuver. This would lead you to check the wiring harness that carries the power steering pressure switch circuit underhood, because it is likely that powertrain movement (during WOT) is stretching the harness, causing an open circuit. This kind of information, while not airtight, may be very helpful in diagnosing intermittent conditions. Besides, it may be the only information you can get about a failure and the only chance to find the cause of an intermittent.