I got a check engine light code, 0504, Automatic Transmission Control Unit Signal to ECU. What could cause this? Anyone have this before? Thanks

 

had one over a year ago, dealer ran a diagnostic and found nothing, reset and all ok, I would'nt have bothered with the dealer since it was the 1st time it went off but I was heading out on a 1000km trip so better safe than sorry, the code has not reappeared, dealer thought it may have been moisture in a connector. Reset it and see if it reappers before going to the dealer.

 

I have that all the time...but I'm drop resisted so... Are you noticing harder shifts. Sounds like the lines running to the Dropping Resistor have shorted and are causing it to shift FLP all the time. The ECU recognizes as the TCM when it is infact the DR.