2000 Peterbilt 379 with Detroit 12.7 60 series . Had ecm go bad but got it going with a borrowed ecm of a Freightliner. The ecm repair place has sent me 4 ECMs including a genuine Detroit rebuild and they all do the same thing. Everything starts and runs fine but the warning beeper beeps. No check engine light or stop engine lights. The beeper quits when you move the accelerator pedal just the tiniest little bit. Like not even enough to increase engine speed. Take your foot off the pedal and the beeping comes back. Same thing with the cruise switches. Can set the idle up and the beeping stops. Back to idle beeping starts. It did not do this with the borrowed ecm. In the process of tearing the harnesses out of it but looking for insight.
I believe it has to do with the chassis the entire game from. IIRC, a decade ago we had an N14 ECM in a Kenworth #### the bed and replaced it with one from a Freightliner. Ran into similar quirks as you are having. We had to rewrite all of the parameters to be copacetic with the Kwhopper.
The ECMs I’m getting are supposed to be programmed to my serial number. I don’t understand why an ecm from different brand of truck didn’t cause this problem though. I really don’t get what makes it beep when there are no warning lights on. Every ecm I get does show some stored codes though. No active codes. Auxiliary output voltage high, coolant sensor input voltage high, boost sensor input voltage low, oil pressure sensor input voltage high, tps voltage low. I checked all these voltages in the harness and they are good.
