I had this dreaded problem and wanted to share because I didn't see much info for a fix out there on this. A bunch of nonsense about inserting and leaving keys in for 15 minutes did NOTHING. This is my first time posting so if this isn't the right place or breaks the rules go easy on me.

truck : 04 FX4 / tune /6inch lift, 35's and other mods

Background:

• Worked fine and now won't start/won't crank.
• No dash or gauge cluster, windows won't work/ dome lights don't work/radio no power
• No check engine light
• PATS (Security light in front driver corner near windshield Flashes rapidly in on position)
• when I turn the key I can hear the fuel pump (aka a noise behind the cab)
  • and clicking from the the ash (aka throttle body startup proceed)
• There can be variations of these symptoms

Fixes:

• First and foremost I checked battery/alternator
  • both good
  • no change
• tried magical sequences about turning keys back and fourth
• leaving key in for 15 minutes
  • didn't work
  • no change
• Checked all fuses in the passenger foot kick panel
  • no bad fuses
• swapped the PCM relay for the fog light relay
  • no change

At this point I got into my tuner and pulled the DTC code. Scanner pulled B1681 - PATS Transceiver Module Signal Is Not Received. I was pretty angry at this point because I knew I would probably have to call my dad to help me chase down wires and see where there was a short. But first I decided (with help from these forums) to swap out:

• Fuel pump Control module
  • This didn't fix the issue but it was corroded and just another thing waiting to leave me stranded!
  • you should replace this if you are already chasing these issues down
  • YT link below on how to change
• Halo transceiver to read the key chip
  • Did pinout test and it passed
  • decided to replace anyways
  • After replacing truck still wouldn't start
  • pinout test PDF attached

I was REALLY upset at this point because I realized how big this job was getting. I asked my dad who has a background in electronics to help me check all the junction box and fuse panel. In looking at the left fuse panel we noticed quite a bit of rust on the ground strap (see picture) once pulling back some of the plastic panels. My dad had me remove them to check continuity on some of the grounds. Thats when literally chunks of metal broke off. The metal ground was so rusted that when I tried to unscrew the bolt a chunk of metal broke out. We moved over to the driver side just for giggles and to no surprise it was in the same shape. After removing both chunks of metal that held the threads in from the ground eyelits; we moved them to new grounds and truck started right up.


I pulled 2 pictures from the other forum (I didn't take any pictures during) just to show what mine looked like:






So if you have wacky stuff going on with the truck no starting. Certain things on but others off, check for body rot in both driver and passenger foot kick panels.You will probably need to pull some plastic panels back to get a good luck. I moved mine to new good chassis grounds (ensure you remove any paint!) coated the area to not rust and all is well. Good luck!

Also here is a link about what it looks like and how to fix it. Don't want to create a how to if someone already has.

https://www.f150forum.com/f4/truck-w...update-383304/ - Procedure starts about 1/2 way down the page/

 

Congratulations on a successful (eventually) repair. I will offer a critique and observation that may help you and others in the future.

You focused on a single in-your-face (literally) symptom (the flashing PATS light) instead of the entire group of failures that were known. That caused considerable effort to be spent on a single secondary symptom to the exclusion of all the others resulting in considerable wasted time and effort chasing a PATS issue when that was actually a secondary symptom. In your case, the lack of the instrument cluster operating also resulted in secondary symptoms for items that power off the accessory delay relay that has to be energized by the cluster (radio, windows, courtesy lighting). In your truck, ground G200 in the LH A-pillar is common to both the cluster and the PATS transceiver. Most likely, there would have been additional symptoms found if a deeper dive had been taken (wipers, washer, and a few optional content features). FWIW, repairing G200 on the driver's side (not pictured), is what would have solved your noted issues. The grounds on the passenger side were poised to fail but hadn't yet fallen off that cliff during "normal" operation as there were no issues noted related to it.

When multiple faults are present, it's important to identify what is common to as many of those failed functions as possible. These are usually indicative of power feed or ground issues. Additionally, if unusual co-dependencies are observed, that almost always points to a failed ground.

Body rot in this generation of truck is becoming more and more prevalent (I see a thread on this almost every week or two across multiple forums) as salt and water ingress take their toll. Because the critical grounds are "down low" on the A-pillars, their failure is often the first indication that the cancer is present and spreading. Simply moving the grounds to a higher point is a solution that will restore the electrical function of the circuits and extend the useful life of the truck.

Again, thanks for sharing your experience.

 

"When multiple faults are present, it's important to identify what is common to as many of those failed functions as possible. These are usually indicative of power feed or ground issues. Additionally, if unusual co-dependencies are observed, that almost always points to a failed ground."
- I appreciate the good constructive feedback. Being not well versed in electronics this was an eye opener. I can see how it's easy to go down the rabbit hole of PATS, chasing issues/throwing parts and getting nowhere fast.

"Again, thanks for sharing your experience."
-Glad to join. Hope this helps out anyone frustrated with similar issues.