PCM reflash for corrupt file?

[PsycOhm]

Hello everyone! This is my first post on this forum.

I believe I have an unusual issue with my 2021 ST.

To preface this, I'm relatively familiar with auto mechanics but not a mechanic whatsoever.

So yesterday my A/C stopped working. Leading up to yesterday- I had super cold air, no unusual function of the compressor (rapid on/off or weird sounds from under the hood).

And now today, nothing. The compressor stopped engaging the clutch. Ok, so I went into my scanner to see if there was something inhibiting it from turning on (ie. temp sensor etc.) and I found nothing. So, as I am not a mechanic my next step was to check the Hi and Low side to see if it had leaked. That is where my diagnosis ended as it made more sense to hire someone to come out and run their own diagnostics.

The mechanic came out and was able to conclude the system did not have a leak, but though his troubleshooting, he concluded that there was a corrupt file on the PCM! His inability to be able to see the status of the compressor led him to look into the computer and see if it was commanding the compressor on. Thats where he saw that there was some kind of discrepancy, and it wouldn't allow him to see the activity through the PCM. His diagnosis was that the PCM needed to be reflashed and updated to correct the problem.

I'm sure I can do a better job of explaining this, but its a little challenging for me my apologies.

So, I guess my question is, has anyone had a similar issue? I'm not entirely sure how to go about correcting this. Any help is greatly appreciated.

Thank you!

EDIT- 30,426 miles and no modifications

 

[Polizi212]

I am not aware of a PCM reflash tool, but if he is not able to find and communicate with the Compressor sounds like it has lost a data connection. Any Check Engine lights or codes pulled from either scan? could be a data connection to the PCM or a bad PCM Might want to see if anyone else chimes in or just take it to Ford and let them diagnose it!

 

[PsycOhm]

I am not aware of a PCM reflash tool, but if he is not able to find and communicate with the Compressor sounds like it has lost a data connection. Any Check Engine lights or codes pulled from either scan? could be a data connection to the PCM or a bad PCM Might want to see if anyone else chimes in or just take it to Ford and let them diagnose it!

To answer your question, no there was no CEL or DTC present. I did notice this afternoon when I was working on it, there was a fault with the ABS module. There was an issue with the pump motor control, battery voltage, and lost communication with instrument panel cluster control module.

EDIT- I also observed that the freeze frame from the ABS fault event had recorded the external temperature sensor reading 415* F. I believe that this is also around when the A/C stopped working. (I don't think it takes a mechanic to know it was nowhere near that temperature anywhere in or around the car).

Coincidence? I have no idea, but that was something that I had observed.

I believe my next step should be to take it to Ford for a PCM update.

 

[Polizi212]

Losing communication could be a wiring issue. Perhaps rodents have entered the vehicle and gnawed on wires. or there is corrosion on the connectors. if you were in the great white north I would suspect corrosion. West coast I suspect could be either. a thorough inspection for chewed wires under the hood where you can just to see if any were damaged might be in order! Also did you check fuses for the AC system?

 

[PsycOhm]

Losing communication could be a wiring issue. Perhaps rodents have entered the vehicle and gnawed on wires. or there is corrosion on the connectors. if you were in the great white north I would suspect corrosion. West coast I suspect could be either. a thorough inspection for chewed wires under the hood where you can just to see if any were damaged might be in order! Also did you check fuses for the AC system?

Well I suppose that I have more that one issue at hand here...

In hindsight, I had noticed that an ABS fault had been stored in the past.. I got a CEL for the purge canister solenoid valve which I replaced about 2 months ago, but I saw the ABS issue and just cleared it not thinking anything of it (I chocked it up as it was "just a ford thing").

Guess I should have looked into that further. A wire problem seems like the only likely cause of this. hm..

My location isnt prone to rodents, but we did buy it from a dealership in Texas and I believe that it was originally purchased in Florida..

Now that I am thinking a little further into this, I am beginning to think that a reflash of the PCM may be a solution to a symptom and not necessarily the bigger problem at hand.

EDIT #3- Yes, all fuses have continuity.

EDIT #4- Now that I've looked through some wiring diagrams through Mitchell, the ABS module is connected to the HVAC system through the auto start/stop (to turn the A/C off during auto stop conditions)..