I been trying to diagnose my truck and finally got the wiring diagrams from the Ford site for my 2017. My symptoms were a long crank with a little bit of a fuel knock when it finally starts and a loping, rough idle. The truck is stuck in limp mode with all the codes that are firing off, the codes are numerous but many are on the VrefA circuit which is the motor harness mainly.

The FRP fuel rail pressure is one of the codes so I started diagnosing there. What I found off the bat was that I didn't have 5V to the Vref wire but my signal wires are running 5V. I took the fuel temp and pressure sensor connector off along with the accelerator valve connector and both those had no voltage. I checked and found the Vref wire is shorted to ground so I unplugged my engine harness from the PCM and verified my vref and signal return (ground) were not shorted and they all checked out OK the best I could tell.

I plugged the harness back into the PCM and back probed PIN 21 which is Vref, I am not getting any voltage through that PIN from the PCM KOEO. Does anyone know where to go from here? Bad PCM? what caused it?

Its going in to the dealer in a couple days but if I can do a little more hunting and find out what is wrong that would be great.

 

 

check the wiring by the parking brake. That wiring has been know to cause problems for those that use the parking brake.
Might need to take it apart, reconnect and relocate.

 

I looked around and didn’t find anything suspect- do you have any more info on this or posts to reference? If you can say what that harness plugs into then i can find a wiring diagram to see what it affects.