2012 C3 - Engine fault, repair needed - ECO deactivated

[Lunacake]

Hi all. I will try my best to be descriptive with my issue.

My car is 2012 C3 1.4 HDi 70 Mk2, Automatic. I've owned the car since september 2024

Since i got this car, around 80% of the time i turn the key (not to ignition, just to electrics) the screen beeps and comes up with "Engine fault, repair needed" followed by "ECO deactivated" the ECO off button on the side then starts flashing its little light. Stop/Start has never once worked in the year i've owned this car and been seeing this error.

When i was getting the timing belt changed at the start of the year, i asked my mechanic if he could take a look at the fault too. After, he didn't seem worried but honestly he wasn't very helpful about what he found out and and was quite vague, I don't think he could figure out what the error was. he suggested the battery was old and might help to replace it. I did that, making sure it was specifically a Stop Start battery, but the error has persisted ever since then. I've tried to look at the error myself with a OBD reader but it wasn't finding any codes when i plug it in (with the fault notice appearing on the car)

The car itself runs fine and smoothly so i'm under the assumption this is a problem with the SS system and nothing serious with the engine itself?

My (english) MOT is coming up soon and i'm worried the fault message will automatically fail the car (the check engine light does disappear upon ignition but the orange service text stays lit) I really would like to avoid £150 to have someone plug their scanner in and tell me what the code is saying, any chance someone here has an idea of what could be going on?

On another note, I've found someone who says he can enter the ECU and just permenantly disable the SS functionality in the hopes of stopping the error from ever appearing (i don't care about SS not working lol), is this fine?

Thank you for any help!

[PaulC5]

Could be the battery is not fully charged so the stop/start will not work. Do you do mainly short trips in the car or mostly long ones - if short they may not be enough to keep the battery charged enough, this is the case with our 308 so it saves me having to switch off the stop/start to help preserve the battery and starter. There might also be a large capacitor that is used by the stop/start and this might need replacing, possibly located inside a front wing.

I would not let anyone start messing with the ecu programming, they might cause other problems.

Engine fault repair needed might not be connected to the stop/start and could be something else - you might need to use a dealer with their diagnostic equipment to find out what it is, if not obvious.

[Lunacake]

Since installing the new battery I've done several long trips to the beach with the family but mostly short local jaunts with it. Would the battery not having enough charge really give a engine fault error though? feels too vague to me.

I have read that a capacitor like that might exist but weirdly for my car i can't seem to find literally any information about this other than some vague posts about it in forums such as this. Not a single youtube video showing how to replace it? How can that be, theres a video for everything these days! lol

[Lunacake]

A kind Gentleman i found on FB scanned my car for free and the error is [ P1A9C - Energy Accumulator State Of Health]. So as suspected it wasn't the main battery but the capacitor in the system.

Question now is, do i need to urgently sort this out? i'm still worried it will fail the MOT if it beeps with the engine fault, even though the check engine light doesn't stay, the service light does.

[PaulC5]

You could ask your MOT garage whether it might fail before you book it in.

If planning to work on one of those capacitors you might need to be careful in case it has a high voltage/amps.