Our coach has a switch labeled "Eng Diag" on the dash under the air conditioner controls. Any clues on what that switch does and how to use it?

Hi Gleen

I believe that this is not for "personal use".

Here goes the "non technical version":

This is for the service guy's (you know - the ones with propellers on their hats ). Their can hook up their instruments and get a read out of any faults that your unit may be having.

I am sure that someone can give you a more correct explanation, but this is basically it (I think).

Glenn,
I believe that under certain conditions, eg. "Stop Engine light" illuminated on dash; a Cummins tech can talk you through the procedure. You need to be stoped and able to turn the ignition off and then on again. Not sure of the exact sequence. But when done correctly the light in the switch will flash a code that the Cummins tech can interpert. Not all problems will throw a code, but when Cummins hooks up a PC to the diagnostic plug any prior codes can be read. Hope you never need to use the switch.