I have a 2015 Ford fiesta SE. I purchase a ECU online which I had to give my VIN# for programming. When I receive ECU in mail install I'm my car,car didn't start so I had locksmith to program my key and it started. But I receive code of the ecm not communicate with the car and the scanner picks up another VIN instead my VIN that should have been program to the ECU I purchase. What would happen if I swap back my original ECU with VIN to my car will I be able to start car or do I have to call keysmith again to have my key reprogram back to original ECU for my car.

  • Welcome to Motor Vehicle Maintenance & Repair! It sounds to me like they just sent you a used ECM without making any changes. Personally, I'd send it back and get a refund, then take your money elsewhere. Commented Dec 5, 2022 at 11:59
  • Will the ECM that I purchase online which has a whole different VIN number of the car so it does drive but I've been having a lot of issues and codes I'm not sure if it's related to the ECM. The other day I was driving to pick up my kids from school and my circuit team Bell broke as I was driving so I had to get the car towed back to the house and I purchased a serpentine belt at Napa and I put it on myself Commented Dec 5, 2022 at 22:19
  • I would love to get my money back but it works for my car the car runs just a lot of faulty codes coming up but the original ECM doesn't start the car do I need to program the key like I did for the ECM that I purchase which works other than having a different VIN number Commented Dec 5, 2022 at 23:00

2 Answers 2


The locksmith didn't actually program your keys since keys are stored in the body control module on this model. The programming that needed to be done is called "Parameter reset". This feature matches the synchronization code between the PATS (immobilizer) inside the body control module and the PCM (ecu). Without these two matching the pcm would not allow the start command, fire or fuel.

Generally when a parameter reset is performed it changes this sync code that links the pats and pcm together. Your original pcm should no longer match and the parameter reset function will likely need to be performed again unless the locksmith did not complete the procedure (if the car started and ran with new pcm then it was completed)

  • So I did swap back the original ECM back into my car which it wouldn't start up so I swapped the ECM that I have programmed that I purchased back into the car and it started right up so I'm thinking and up and I asked you this if I wanted to have my original ECM back into the car cuz right now I don't think anything was wrong with it I would have to reprogram my key to the ECM because it won't start when I do connect the ECM back into the car the original one what I have to have a locksmith to do what he do to get the car started and running. Commented Dec 5, 2022 at 22:21
  • It needs to have a parameter reset done.
    – narkeleptk
    Commented Dec 6, 2022 at 2:44
  • Is it possible for me to do the reset or do I have to take to mechanic. If it's possible for me to do it, do you mind explaining the steps Commented Dec 6, 2022 at 5:17
  • you need a diagnostic tool capable of performing PATS functions.
    – narkeleptk
    Commented Dec 6, 2022 at 5:24
  • Where do I get that? How much does it cost. I been spending money to fix the problems. Since I remove my ECU from my car yesterday and then I put it back in my car. I'm receiving more codes like the ECU not communicating with everybody so codes are coming up Commented Dec 6, 2022 at 5:32

Assuming that the original ECU is still functional (I mean why did you swap it out anyway??) then it should still work.

The key's ID is stored in the ECU and nothing is changed in the key itself. So the old ECU should still recognize the key.

  • 1
    This is right if keys are stored in ECU on some mid 2000 models but is wrong for this model year. Keys are in BCM.
    – narkeleptk
    Commented Dec 5, 2022 at 12:40
  • Well I swap the my original ECU back in but wouldn't start so I swap back the program ECU that I purchase on online with whole different VIN. I swap my original ECU out because it was scanned and several codes came up. Like ECU/PCM not communicate all because someone was replacing my battery in the dark cause my battery died in public so he touch the positive terminal to negative on battery next thing Sparks and a little bit of smoke came from the battery or near the battery. Commented Dec 5, 2022 at 22:13
  • I did swapped my original ECM back into my Ford fiesta which it wouldn't start so I swapped the ECU that I purchase that doesn't have the same VIN number to my car it started up so if I wanted to change my original ECM back into my car do I need to have my locksmith come in program my key to the car or to the ECM Commented Dec 5, 2022 at 22:47
  • Can I swap back the original ECU back into my car with the correct VIN cause the new ECU I purchase online is not showing the right VIN for this car. And now I scan the car and gets all types code on this car. Would that be because the ECU with different VIN? Commented Dec 18, 2022 at 23:32
  • Codes P0504-00. U0401. P0573-00. P160A-00 Commented Dec 18, 2022 at 23:37

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