Hello forum! I posted this to the general forum but I feel like I should post this here in this section as its geared towards this generation but I have a little problem on my hands hopefully I can get a direction to go in. I have a 2001 F150 Lariat with the 5.4L
I had an issue before where it would only crank over and not start before and I was told by a buddy it needed the key to be reprogrammed so it fixed it for then and now its starting to do it again, the theft light blinks and odometer just dashes, but strangely when I first checked it with my Autel scanner the first time it said there was no communication between the scanner and PCM, I did what it said on screen and wait 10 seconds and try scanning it again to see if it would connect with the software, I did and it finally communicated, and I went to turn the truck on like and it turned over and started like nothing, no theft light blinking, nothing was flashing, no codes.

I took the scanner out and it failed to start. Then I plugged it back in and did it again and it lost communications again and I did the same thing but the second time around it started without the scanner plugged in, then to see if it magically fixed itself I waited ten minutes and tried to start it again and it didn't. It will only start with a scanner plugged in it. I am not sure if it is a PCM issue but I know it probably may be, I just wanted some opinions on the subject and see if it sounds like that to y'all. Thanks for reading!

 

Alright, next time it does it, wait for it to stop rapidly flashing. It will then flash a two digit code, and i bet 95% it'll be a code 16. Seeing the dashes in the odometer does confirm its a loss PCM connection. I can't tell you how many times I've seen this, and its the PCM relay, fuses, or both. I suggest checking and swapping your heated backlight relay for your PCM relay. Here's a video I made on it a while back.

 

Holy cow, you were 100% right. Thank you so much you have no idea how appreciative I am!

 

hello! I’m having the same issue you’re demonstrating with the relay removed but I have swapped with a known working relay from another f150 (same generation different spec) and still have dashes, code 16c crank no start.

do you know where I should begin to diag? I’ve swapped with a reprogrammed pcm, cluster, lock cycl. OBD doesn’t communicate but I assume that’s due to theft flashing?