I am having a problem where my truck goes into limp mode within the past few weeks. The code I am getting is PO641. This would indicate a problem with my wiring harness or one of my 5v reference sensors. To diagnose the problem I have read that I need to log the 5v reference pid and unplug sensors until the voltage is correct. Is this true? If so how do I do this? I do not see this PID in the list on hptuners.

Someone else had this problem and have any good idea of what it could be? I do not see anywhere where my harness is shorted.

 

5v circuit A stuff on the E38 is Cam sensor, MAP sensor, Tank Pressure, Oil Pressure, A.C Pr, and throttle body.

So what you could do is log those sensors specific voltage with key on engine off and see what it gives you.

Interesting problem...par for the course on that truck

 

Thanks Richard. I will try that. This truck is a piece of **** and if I could get rid of it I would.