Diagnosing Intermittents

Most tables have one result which reads The Problem is Intermittent. This means that the conditions that were present when the DTC set are no longer present. This does not mean that the problem is fixed. The problem is likely to return in the future and 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 2 ways: through the Snapshot data and by driver observations.

The snapshot data, whether Freeze Frame and Failure Records or scan tool Snapshot, can be used to check data parameters to see if the parameters fall within a normal operating range. For example, a snapshot Manifold Absolute Pressure (MAP) parameter value of 100 while the engine was idling is not normal, and would indicate that the MAP sensor voltage went high due to either 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 P0403, you find out the driver Noted that the MIL only comes on after an extended wide open throttle maneuver. This would lead you to check the wiring harness that carries the EGR control circuit underhood, because it is possible that powertrain movement during WOT is stretching the harness and causing an open circuit. This kind of information, while not fool-proof, may be very helpful in diagnosing intermittent conditions, may be the only information you can get about a failure, and the only chance to find the cause of an intermittent. Refer to Intermittent Conditions in Symptoms for more information. Intermittent Conditions