How do you read a J1939 DTC?

Modified on Wed, Nov 8, 2023 at 10:18 PM

A J1939 DTC contains four fields that relay information about the fault being reported by DTC. These fields are:

  1. Suspect Parameter Number (SPN): Represents the SPN with error. Every defined SPN can be used in a DTC.
  2. Failure Mode Identifier (FMI): Represents the nature and type of error that occurred, e.g., value range violation (high or low), sensor short-circuits, incorrect update rate, calibration error.
  3. Occurrence Counter (OC): A counter that counts the occurrence of the error condition for each SPN and stores this even when the error is no longer active.
  4. SPN Conversion Method (CM): Defines the byte alignment within the DTC. The value “0” represents the method shown in graphic “Structure of a DTC”. If CM has the value “1”, a distinction must be made between three previously valid methods; this must be known for the system.

Was this article helpful?

That’s Great!

Thank you for your feedback

Sorry! We couldn't be helpful

Thank you for your feedback

Let us know how can we improve this article!

Select at least one of the reasons

Feedback sent

We appreciate your effort and will try to fix the article