When I program a single ECU, sometimes I notice that other ECU’s are also programmed, Why is this?

ANSWER:

Certain ECU’s and their software must be matched (compatible) with other ECU’s.   So it can be expected to have multiple ECU’s programmed when only one ECU has been selected.   This is due to internal systems dependencies.  An example is if the ECM software is updated, it may be required to update the ACM for proper functionality, drivability and OBD compliance.  Note that this is only for OBD2013 and newer vehicles.

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