[the roadie]

How many miles? Those issues are all related to serial data messages coming from the DDM, and the honk might be a security-related confirmation that the DDM just sent a "lock door" message. You might try configuring Driver 1 and 2 to NOT use the horn as the fob lock confirmation, if they are using it now.

The issue could also be just the switch in the door latch assembly that tells the DDM that it's locked. That would explain the display and the lights, but maybe not the honk.

The DDM may be getting flaky with age or water contamination, or it might be flaky, intermittent wires in the middle of good-looking insulation. The driver's door gets the most flexing of this harness hear the hinges. You might pull the boot back and look at and flex the wires to see if any feel funny.

 

[the roadie]

Aftermarket remote starts are VERY suspicious items, depending on the brand. I'm not an audio system specialist, but I could move this thread to that forum if you'd like. I should have asked first, because I think they MUST send data on the bus to bypass the security system. Can you, or have you, ever disconnected it as an experiment? I might have to sign off supporting this issue since it's no longer my specialty. Plenty of other volunteers, though.