APU Runs for a few minutes, shuts off with red ENG light

When I had apu issues it was always the ground wire going bad.

 

I dunno. Shop used to tell me that. I was company. Never owned my own truck. Sorry.

 

You gotta look. Take down the bottom plate if it's a trip pack, it's usually underneath towards the back side.

 

mine has done this you should trying bleeding the air from anti freeze on the therm stat housing there is a bleeder valve on top. If there any air in the engine it will shut down. you know how to clear it out turn the power off press the reset bottom then restart. Have owned mine for 6 year had this happen twice

 

see you had a temp senor replace bet there some air in your system it not the wires if you got code with a red triangle putting my money bleeding the tripac engine

 

It on top of the unit under the bunk on the side towards the back it petty well hidden but you need to find it or it won't restart till you do. It the size of pencil eraser push it in till it clicks

 

There are three things that will cause an Eng code.

1. Low oil pressure (probably not it)
2. Switch inside unit is off ( will not run at all, immediately trips code)
3. High coolant temperature (likely culprit)

Did they shut the water valves off to the APU for some reason? If yours has the Arctic package, make sure the water valves are open.

Then, press the reset button on the outside of the control box. (Large black metal box under the bunk with a bunch of wires going to it)