Engine Control: Overview

The diagnostic trouble tree charts and functional checks are designed to locate a faulty circuit or component through logic based on the process of elimination. The charts are prepared with the requirement that the vehicle functioned correctly at the time of assembly and that there are no multiple failures. Trouble tree charts are designed to be used only when a diagnostic trouble code or flag is present.

The PCM performs a continual self-diagnosis on certain control functions. The PCM's language for communicating the source of a malfunction is a system of diagnostic trouble codes. The diagnostic trouble codes are two digit numbers that can range from 11 to 99. When a malfunction is detected by the PCM, a diagnostic trouble code is set and the malfunction indicator lamp (MIL) is illuminated.

Diagnostic trouble code:
Suspected failure detected in the engine or transaxle.

Information flag:
A diagnostic aid used when a diagnostic trouble code or intermittent problem occurs. It does not necessarily indicate a failure.