Diagnosing Intermittents

Most diagnostic 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, this simply means that the problem is intermittent. The problem was present but is not present now.

And the problem is likely to return in the future so the problem 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. You can accomplish this process in two ways: through the Snapshot data, the Freeze Frame data, and the driver observations.

You can use the snapshot data to check the data parameters in order to determine if the data parameters fall within the normal operating range. For example, a snapshot TP sensor parameter value of 100 percent while the engine was idling is not normal and would indicate that the TP sensor voltage went high either due to an open in the sensor return circuit 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 P0300, you will find out that the driver noticed that the MIL only comes on in the rain. This would lead you to check the secondary ignition wiring, because it is likely that an ignition component is arcing to ground when wet.

This kind of information, while not airtight. may be very helpful in diagnosing intermittent conditions. Besides, this information may be the only information you can obtain about a failure and the only chance to find the cause of an intermittent.

CAPTURE INFO
Selecting this option on the scan tool allows the technician to record the Freeze Frame data. The scan tool stores the data. When starting the diagnosis, capture the Freeze Frame data. Later this information can be reviewed, even if the ECM or the battery has been disconnected, or if the DTCs were cleared during a diagnostic procedure.

ECM SNAPSHOT
The ECM snapshot feature is designed to assist in a diagnosis of intermittent problems. When an ECM snapshot is taken, a predetermined subset of the ECM's data parameters at that moment in time are stored for retrieval and for use in diagnosing a problem. The scan tool can be set up to take a data snapshot when a specific DTC sets, if any DTC sets or when the DTC is manually triggered with the scan tool.