need code help

About a year ago, I was about 200 miles from home when I encountered a very strange problem on my 2018 modified/tuned FiST. I started it up after being parked overnight, drove down a hill and as I made a left turn the engine stalled. Had neved stalled on me before but it restarted right up. About 50 feet later, I made a right hand turn and it stalled again. It restarted but this time there was no response to the throttle, it would only idle. I happened to have a 10mm wrench with me, so I disconnected the negative battery terminal and let it sit a few minutes, then reconnected it, and it started right up, behaved normally until I took another turn. I tried disconnecting the battery again but this time it would not even turn over, got a wrench sign/repair now“ message. Stuck in the middle of nowhere, I called for a tow to the nearest Ford dealer. VERY long story short, the service rep called to say I had a faulty sensor. Not thinking much of it (really, not thinking !), I told them to fix it. When I got the bill, I was astounded. They had replaced my passenger seat cushion, saying the sensor was part of it. The only sensor I could imagine being in the seat cushion is the passenger air bag sensor. But I paid the bill, glad my car was fixed and I could go home. …… Until yesterday, when it started doing something very similar except this time I did not have to turn a corner for it to shut down (but turning corners still did cause it to shut down). Also, again, started but would only idle. Fortunately, this time I was close to home as I had just left home, driven a mile or so. I nursed it back home by disconnecting the negative cable several times whenever it stalled. This morning I put a code reader on it and got code P2610 ”Internal Engine Off Timer Performance”. I erased the code and then took it for a test drive and it behaved normally. Ran it through lots of corners, no problem. Anyone have a clue as to what might be causing this problem ? I hate to bring it back to Ford after the last experience. Reluctant to drive it any distance. Could this somehow be triggered by the changes to the PCM when it was dyno tuned ? (It had been driven for many moons by the past owner after the tune, so I’m inclined to think not). Both times, last year and this time, the fault occurred in the first few minutes of operation after being parked overnight. Any help/advice would be greatly appreciated.About a year ago, I was about 200 miles from home when I encountered a very strange problem on my 2018 modified/tuned FiST. I started it up after being parked overnight, drove down a hill and as I made a left turn the engine stalled. Had neved stalled on me before but it restarted right up. About 50 feet later, I made a right hand turn and it stalled again. It restarted but this time there was no response to the throttle, it would only idle. I happened to have a 10mm wrench with me, so I disconnected the negative battery terminal and let it sit a few minutes, then reconnected it, and it started right up, behaved normally until I took another turn. I tried disconnecting the battery again but this time it would not even turn over, got a wrench sign/repair now“ message. Stuck in the middle of nowhere, I called for a tow to the nearest Ford dealer. VERY long story short, the service rep called to say I had a faulty sensor. Not thinking much of it (really, not thinking !), I told them to fix it. When I got the bill, I was astounded. They had replaced my passenger seat cushion, saying the sensor was part of it. The only sensor I could imagine being in the seat cushion is the passenger air bag sensor. But I paid the bill, glad my car was fixed and I could go home. …… Until yesterday, when it started doing something very similar except this time I did not have to turn a corner for it to shut down (but turning corners still did cause it to shut down). Also, again, started but would only idle. Fortunately, this time I was close to home as I had just left home, driven a mile or so. I nursed it back home by disconnecting the negative cable several times whenever it stalled. This morning I put a code reader on it and got code P2610 ”Internal Engine Off Timer Performance”. I erased the code and then took it for a test drive and it behaved normally. Ran it through lots of corners, no problem. Anyone have a clue as to what might be causing this problem ? I hate to bring it back to Ford after the last experience. Reluctant to drive it any distance. Could this somehow be triggered by the changes to the PCM when it was dyno tuned ? (It had been driven for many moons by the past owner after the tune, so I’m inclined to think not). Both times, last year and this time, the fault occurred in the first few minutes of operation after being parked overnight. Any help/advice would be greatly appreciated.About a year ago, I was about 200 miles from home when I encountered a very strange problem on my 2018 modified/tuned FiST. I started it up after being parked overnight, drove down a hill and as I made a left turn the engine stalled. Had neved stalled on me before but it restarted right up. About 50 feet later, I made a right hand turn and it stalled again. It restarted but this time there was no response to the throttle, it would only idle. I happened to have a 10mm wrench with me, so I disconnected the negative battery terminal and let it sit a few minutes, then reconnected it, and it started right up, behaved normally until I took another turn. I tried disconnecting the battery again but this time it would not even turn over, got a wrench sign/repair now“ message. Stuck in the middle of nowhere, I called for a tow to the nearest Ford dealer. VERY long story short, the service rep called to say I had a faulty sensor. Not thinking much of it (really, not thinking !), I told them to fix it. When I got the bill, I was astounded. They had replaced my passenger seat cushion, saying the sensor was part of it. The only sensor I could imagine being in the seat cushion is the passenger air bag sensor. But I paid the bill, glad my car was fixed and I could go home. …… Until yesterday, when it started doing something very similar except this time I did not have to turn a corner for it to shut down (but turning corners still did cause it to shut down). Also, again, started but would only idle. Fortunately, this time I was close to home as I had just left home, driven a mile or so. I nursed it back home by disconnecting the negative cable several times whenever it stalled. This morning I put a code reader on it and got code P2610 ”Internal Engine Off Timer Performance”. I erased the code and then took it for a test drive and it behaved normally. Ran it through lots of corners, no problem. Anyone have a clue as to what might be causing this problem ? I hate to bring it back to Ford after the last experience. Reluctant to drive it any distance. Could this somehow be triggered by the changes to the PCM when it was dyno tuned ? (It had been driven for many moons by the past owner after the tune, so I’m inclined to think not). Both times, last year and this time, the fault occurred in the first few minutes of operation after being parked overnight. Any help/advice would be greatly appreciated.About a year ago, I was about 200 miles from home when I encountered a very strange problem on my 2018 modified/tuned FiST. I started it up after being parked overnight, drove down a hill and as I made a left turn the engine stalled. Had neved stalled on me before but it restarted right up. About 50 feet later, I made a right hand turn and it stalled again. It restarted but this time there was no response to the throttle, it would only idle. I happened to have a 10mm wrench with me, so I disconnected the negative battery terminal and let it sit a few minutes, then reconnected it, and it started right up, behaved normally until I took another turn. I tried disconnecting the battery again but this time it would not even turn over, got a wrench sign/repair now“ message. Stuck in the middle of nowhere, I called for a tow to the nearest Ford dealer. VERY long story short, the service rep called to say I had a faulty sensor. Not thinking much of it (really, not thinking !), I told them to fix it. When I got the bill, I was astounded. They had replaced my passenger seat cushion, saying the sensor was part of it. The only sensor I could imagine being in the seat cushion is the passenger air bag sensor. But I paid the bill, glad my car was fixed and I could go home. …… Until yesterday, when it started doing something very similar except this time I did not have to turn a corner for it to shut down (but turning corners still did cause it to shut down). Also, again, started but would only idle. Fortunately, this time I was close to home as I had just left home, driven a mile or so. I nursed it back home by disconnecting the negative cable several times whenever it stalled. This morning I put a code reader on it and got code P2610 ”Internal Engine Off Timer Performance”. I erased the code and then took it for a test drive and it behaved normally. Ran it through lots of corners, no problem. Anyone have a clue as to what might be causing this problem ? I hate to bring it back to Ford after the last experience. Reluctant to drive it any distance. Could this somehow be triggered by the changes to the PCM when it was dyno tuned ? (It had been driven for many moons by the past owner after the tune, so I’m inclined to think not). Both times, last year and this time, the fault occurred in the first few minutes of operation after being parked overnight. Any help/advice would be greatly appreciated.

Sorry I kept reposting this because it was not appearing in my listing in the menu !

The most common reason for that code is a weak battery. The Fiesta ST does a lot of very strange things when the battery is getting old--it will still start the car, but doesn't provide quite enough stable voltage to the various computers. After you swap the battery be sure to perform the battery management system reset.

A secondary reason can be the wiring, including bad connectors, weak grounds (usually corroded).

Thanks for the help. The battery is less than a year old and the voltage seems quite good (12.6 with only driving).

The list of possible problems goes from the battery to the wiring/grounds, to the ECM being bad, with a side detour through sometimes a fault in the coolant temperature sensor.

Update: after Dave (the original owner) corrected that it has a flash tune, not dyno tuned, I spent some time reading about this code and the many possible causes. After clearing the code, I drove it for about 30 minutes with no issues. I let it sit overnight, then checked for codes in the am (since it can generate a code with the car shut down). No faults found. So I decided to try driving it around town. Once again, about 2 miles from my house, it shut down after turning a corner. It restarted but idle only, wrench sign reappeared. I disconnected the negative cable, then reconnected and it started up, ran normally until I turned a corner again trying to get back home. Got a message that it was now in “Immobilizer” mode. Called for a tow. After sitting for 30 minutes, car started up and I drove it onto the tow truck. After getting home, it started up again, backed it off the truck and got it back into my garage. I’m thinking there’s a fault in the ECM that is well beyond my ability to diagnose, let alone fix. Being in the AZ boonies, I am not inclined to take it to Ford again and I have not been able to find any specialized service for these types of issues within 500 miles of my home. Currently, I suspect an internal fault. No urgency about getting it fixed, I have a truck I can daily drive. I will take my time to carefully check other possible physical causes (loose connections, corrosion, etc.). Then, since it costs nothing, I’m thinking of trying loading the OEM tune to see if the problem continues. If it does, I’m thinking of getting a new ECM, see if that cures it. If it does, then reflash a tune. If anybody has better ideas, I’d be very happy to hear them. Steve S, thank you again.