508 hybrid4 STOP! Message & U1207 fault

[Mr Box]

Hi. First time posting.
(Edited to hopefully get some responses)

I'm randomly getting the "engine fault, repair needed" message and the STOP warning on the dash, it goes away after I stop and start the engine
My wife's uncle plugged in OBD and found fault U1207 and deleted it. I drove the car for over an hour afterwards and did a couple of short journeys later and no warnings appeared .
Does anyone know what fault U1207 means please?

Rear seatbelt sensors are alerting even though the seats are empty. Does anyone have pictures of what I need to look for to fix this please?.
This started after it was with a mechanic for a week or so and they left the ignition on practically the whole time without realising (hybrid), also resulting in a dead battery. I changed the battery myself, hopefully that didn't cause any other issues ?.

Another issue I get is a loud clunk/crunch sound when driving slowly coming to a stop, like around carparks, start/stop traffic and sometimes when stopping at junctions.
Does anyone know what is happening here?
This also happens when in ZEV mode and the engine isn't running if that helps?

[Mr Box]

Update
The day before yesterday I did a few short journeys and the warnings came up again, I plugged in OBD again but no faults showing?

Yesterday and today I have been driving around the city and motorways for a few hours each day and no warnings have appeared!

[Sloppysod]

It's very possible it's your hybrid battery,the small 48 volt battery in the cabin area.
There's a simple(ish) fix, as instructions in your owners manual, should say, drive for at least ½ hour @ 50mph+ with your petrol engine running most of the time.
These little (size) batteries are charged by the engine.

[Mr Box]

It's very possible it's your hybrid battery,the small 48 volt battery in the cabin area.
There's a simple(ish) fix, as instructions in your owners manual, should say, drive for at least ½ hour @ 50mph+ with your petrol engine running most of the time.
These little (size) batteries are charged by the engine.

Hi. I think your thinking of a different model or vehicle.
The hybrid battery is 200v, quite big and in the boot, also it's a diesel.
The battery is charging and activates normally as far as I can tell.

[Sloppysod]

I may be wrong as I am new to the Hybrid drive train. However, if your car is like most other hybrids, you will have, a traction battery, a 12 volt battery in the engine bay and an auxiliary battery whose location varies depending design, for example,

• Citroën C5X it's under the centre arm rest.

and I think

• Citroën C5 Aircross is in the boot behind the trim.

• DS4 is also under the armrest.

• According to the 508 owners manual yours is located in the boot, under the floor (page 200)

These batteries are small, expensive and seem to cause a lot of Hybrid issues when they are getting 'tired'