Diagnose Functions - Overview

Diagnose Functions - Overview

The Engine Management System fuel/ignition system control module has an on-board diagnostic system for self-diagnosis, continuously monitoring input and output signals and several other functions.

If the engine control module (ECM) detects a fault, some parameters will switch to predetermined, default values, to allow normal as possible operation. At this time a pending diagnostic trouble code (DTC) will be stored together with a number of relevant parameters, to help the fault tracing operation. If the same fault occurs during the next driving cycle then the DTC will be set as permanent and if the fault is emission relevant the malfunction indicator (MIL) will be activated.

If a fault disappears after the DTC has been stored, information about the fault is stored in the ECM. Every time the fault reoccurs a counter counts it. After three consecutive driving cycles without the fault it is allowed to turn off the MIL. For every warm-up cycle that is driven without the fault reoccurring a second counter counts down. It begins with 40 and counts down to 0. When the second counter has counted down to 0 the diagnostic trouble code can be erased from the ECM memory.If the fault reoccurs the second counter is reset to 40.

The On-Board Diagnostic (OBD) system also makes it possible to read out the values and status of a number of parameters through the diagnostic link connector (DLC) using standardized protocol and a standardized scan tool, or the manufacturers diagnostic tool.