Ford P0642

Have an 08 F150 5.4 , crank no start with a P0642, little more advanced than my knowledge. I understand this is a 5v reference issue , looking for any tips or commonality with this particular code . Had 10 yrs a Ford dealer , never seen this particular issue - 25 yr total tech

If you clear this code, does it come back immediately? Or, does it require idle time/test drive?

I'd suggest checking the easily accessible 5V reference sensors under the hood for 5V with a multimeter, KOEO. The FRPT and the TPS are out in the open, if I remember right. Finding 5V would suggest this isn't a hard fault. Finding less than 5V would suggest a hard fault. Start unplugging sensor and monitor the 5V circuit to pull back up.

It is a 5v VREF circuit low fault.

The sensors on this circuit are APP, FTP, PSPT, FRPT.

A good strategy might be to locate the VREF at the PCM and start unplugging sensors until the 5v comes back. (This assumes a good PCM for now)

If it comes back, a sensor may be bad. ( or a short to ground still)

If it doesn't come back, check for a short to ground, unplug the PCM put a test light to B+ on the VREF(harness side), is it LIT? If no, check the PCM itself for 5V. If it is lit, you have a short to ground somewhere in those 4 sensor circuits.

Yes it comes back immediately, that's the only code I have currently, replaced FRP sensor , it was literally falling apart , swapped throttle body with another us to excessive carbon buildup, excessive.

Yes it comes back immediately

That makes things easier. Check for 5V at the FRPT and the TPS, KOEO. Let us know if it's there or if it's missing.