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Diagnosis

Control devices can independently send diagnostic messages (DM). The most important diagnostic messages are DM1 and DM2.

DM1 contains a list of the currently active diagnostic trouble codes (DTC).

DM2 contains a list of the past, no longer active diagnostic trouble codes (DTC).

A DTC describes a defective property in the system. First of all, the code describes a suspect parameter number (SPN) which is in an abnormal state. A DTC is uniform structured and consists of the following elements:

  • Suspect Parameter Number (SPN)

  • Failure Mode Identifier (FMI)

  • Occurrence Counter (OC)

  • SPN Conversion Method (CM)

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