SteveUK

Active Member
Jun 25, 2026
13
3
I've had a series of really weird things happen on my 2021 Leon PHEV. It forgot it had cruise control one day. The next day it forgot it had a radio.
Pulling over and doing a off/on and 10 second restart on the infotainment brought things back.
Then it started to get really weird. Insisting the petrol engine must run when I drove off in EV mode, and then almost immediately switching back to electric motor, then starting the petrol again, then back to electric... (I have a video, it's possessed!). It would even kick in the petrol engine when I was coasting down a hill, even in neutral, and even when braking (I played about trying to find some logic to it!).
I changed the 12v battery (as these are often a source of demonic possession and it is 5 years old).

Booked it into local dealer. Who first told me I can't just change the 12v battery (WTF?! I rebuilt a car engine when I was in my teens FFS!).
Anyway, after their investigation they said it was a fault in the HV battery with a sensor giving erroneous readings, and that they couldn't do it and I would have to go to a battery centre (yes, nearest ones are over an hour away).
Whilst waiting for that booking I didn't bother charging the car and let it go to 0% (it normally doesn't get below 20%)... The car behaved normally as a petrol only (with start/stop).
After a couple of days of that I thought "I wonder..." and I stuck 30% charge into the HV... The car behaved perfectly normally, letting me drive on EV when I wanted, and hybrid. Next day I gave it 100% charge. It drove home on pure EV, and back to the office on pure EV.

A week later it's now behaving perfectly normally and I've cancelled the service booking.

As a software developer by profession, this is screaming "software bug!" at me, and I would like to get the car updated. If it's any indication, the infotainment is version 1790 (iirc), which the dealer admitted is old, but he said they don't do software updates unless SEAT tell them to. How on earth do I get SEAT to tell them to update the software? The dealer also told me it's about a 4 hours job, which I guess was a hint that they would charge me 4 hours of labour for having a cable plugged into the car and then they walk off and leave it updating?
 
Im glad you use the word software since "firmware" is a pre mod word here. With the post 2020 cars fiddling with the software yourself is asking for trouble. Beyond the infotainment system they are done by the dealer. Over air does the infotainment but similar to mib2 standard as I understand you hit an issue at the end of a "train" in old mib2 standard talk. Only a dealer can do it. That might be where the 4 hours comes in.

James who works for a dealer will be more precise than I and fellow owners of that car will know what they are on. Hybrids are a curious world... you might have one of those that James recently explained to me. Personally I'd jump a hybrid and go directly to an EV but that isn't much help. I'll see if I can did up that curious conversation...

Here we are... not one of these then


@James_R is you man on this.
 
I think I remember reading somewhere a while ago (sorry, can’t be certain if I did or remember where 😳) that PHEV’s have a fuel management system. If a PHEV is used mainly on short journeys and is run in electric mode most of the time, the fuel management system will start up and run the internal combustion engine periodically to use the petrol in the tank so it doesn’t go ‘stale’.

@SteveUK - if you’re using your PHEV as above (you’ve not said if you are), then maybe that’s why the petrol engine starts up for seemingly no apparent reason.

As @Tell has said, @James_R is your man and I dare say he’ll be along in due course and provide his input.
 
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I muttered about hybrids getting stuck on the road outside :unsure: . That may be it with the erratic petrol. Honest John's moan was people never managed to charge up the 12v battery since they drove in EV mode and never charged it. James statement above was the 12v got charged from the 48v battery rather than any other way. That would be a new one for Honest John at the time. So the 48v battery does the 12v. How I remember it.

Old firmware it might be the case the case that over the air can't get you over the current version. A dealer job. Over the air is free if even out of contract but has limits if you reach the end of the development version. Cunning.
 
but he said they don't do software updates unless SEAT tell them to. How on earth do I get SEAT to tell them to update the software? The dealer also told me it's about a 4 hours job, which I guess was a hint that they would charge me 4 hours of labour for having a cable plugged into the car and then they walk off and leave it updating?

Your car may have a pending "baseline update", which can be checked via your car's VIN. SEAT periodically assigns these complete updates to VINs when they are available, so what the dealer was talking about is probably that VIN check. If they see on the system that your car has a pending update, usually checked when a car come in for a periodical service, they ask you if you want it. With a baseline update, all control units that have newer versions of their firmware gets updated so it is normal for it to take some time.
 
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