Engine fan on, coolant temp low.

X2

 

Build up air, shut the engine off, turn the key to the on position (make sure the a/c is off and engine temp is low enough that the fan won't be locked), try to spin the fan by hand. If you can't turn it your fan clutch is worn out.

 

You're welcome. Next step is connect cummins insite and see what is calling for the fan..

 

I wouldn't take it to Peterbilt. I would go to a local independent with a proper scan tool or Cummins Insite and ask them to diagnose it.

 

Wasn’t on a Cummins, but I had an intake air temp sensor go bad on a Cat and it caused the fan to run constant.

 

Try unplugging those AC high pressure sensors you found first and see if one of them makes the fan turn off. You may need to stop the engine and unplug it, then start it up. Worth a try, though I don't know if those are normally-closed or normally-open switches. The other thing that will make the fan come on is the coolant temperature sensor.