My sister struck will not start. She has a 2010 F-150 crew cab 4x4 with the 5.4 in it.

Code reader only provided one code and is U0100 "Lost Communication with ECM/PCM "A"

When I turn the key on, the mileage display is all dash lines sometimes. A couple times the mileage will actually display after turning key on so it's inconsistent. When I try to start it, it does nothing. No clicking or turning over.

Battery is only one year old and volt meter showed it had plenty of voltage at 12.6. I put my jump starter on it anyways just in case and still the same issue.

This was taken to the dealer at first and they couldn't figure it out. They suspect water intrusion somewhere but I don't know where that would be and they basically threw up their hands. Perhaps loose or corroded plug or wire? Just not exactly sure where to check first

With the code it's throwing it does have me wondering if it needs a new PCM but I don't know enough about about it or how to check it. Any idea on what I can do?

you're gonna have to dig a bit i think.

i would probably start with a good visual inspection. does the truck live in the salt belt? in the country with mice looking for dinner? i would look over the harness around the connections at the PCM and see if anything stands out.

if you just throw a PCM at it you are just guessing. you're probably gonna want some wiring diagrams and gonna have to do some circuit testing to really know if it's bad or if something else is wrong.

It's been to the beach a few times here in the area around Surfside but it's always been in Texas. I know they have got it stuck a few times out hunting so maybe some water did intrude somewhere finally or something corroded. I've been checking all the fuses and will start checking plugs and such at the PCM

Well I now know the passive anti theft system (PATS) is not recognizing the key as that red light keeps flashing at me at a rapid rate with the key on. I tried connecting to the vehicle with FORScan thinking I could just reprogram the keys but it won't connect. It connects to my other ford and my wife's Lincoln so I know it works. I don't have the original factory key as my sister lost both of them and had a new key reprogrammed to it a few months ago. Can keys go bad?

Still need to do a thorough check of the wiring but I don't understand why I can't get FORScan to connect when it works on my other vehicles.

Might disconnect the battery and let it sit overnight or so then try it.

Location?

So I have some good news. After a couple months of watching you tube video's and research to try and understand how the truck communicates over its network, I fixed it with 1 foot of jumper wire! Right proud of myself after 2 different shops couldn't figure it out.

The issue was I had a break in the wire right before the PCM. The break was on the CAN Low side of the network. I figured this out by testing if the circuit was in tact between PIN 14 on the OBDII port or DLC as some call it to each module. Every module I tested I was able to communicate with until I reached the PCM.

So, I ran a jumper wire from my last know point I knew I had connection bypassing a splice in the wiring harness and boom, it all worked and it cranked right up! Attached is a screenshot of the wiring diagram of my truck communication lines.