cummins m11

It is I think to give you the codes for when there is a fault that the engine management computer registers,Those codes then relate to the fault and then the Mechanic knows where to look and fix/replace ,I was driving an International S-Line with a M-11 Cummins and the damn thing shut down the motor near Injune , was there all day untill someone arrived from Emerald, bloody computers,[ excuse my language all the Poms out there, ]Diagnostic Codes is the correct name.

Egg,
This switch will adjust the idle revs up and down if the feature is enabled(Idle speed adjustment) and when the switch is held up with only the key on(engine not running) it will flash out any active fault codes.
Hope this helps
Dieselman