Intermittent Diagnosis Guidelines

As previously mentioned, intermittent concerns are the most difficult concerns to diagnose.

An understanding of code storage and automatic code erasure is important.

First, codes can only be stored if the ECU has power. The ECU gets primary power from the ignition feed into pin 20. If this voltage is missing or less than 8V, the ECU will not initialize and therefore, a code cannot be stored. A Code 16 (system OK) will be present whenever the module sees the required voltage assuming no other failures are present.

A previously stored diagnostic trouble code will be automatically erased if no system concerns occur for 50 ignition cycles.

Therefore, some codes read out in the System Pre-Check may not result in any trouble found in the Pinpoint Test performed. Inspection and Verification (Start Testing Here) In most cases, this is an indication of an intermittent electrical concern.

To minimize misdiagnosis, use the Intermittent Diagnosis Procedure if no resolution has been reached by the end of a particular Pinpoint Test.

If you are at this point because the warning light is on and you have been unable to obtain any code, go to Pinpoint Test S. This procedure is only meant to address those problems that have been reduced to an intermittent wiring concern.