Warrior193

Extremely poor (and risky) for them to have overfilled by that much - how far above max was it after the service?

Hello, not sure if it's a good assumption that your Banner-branded battery is original - I'd agree it to be more likely if it had been a Moll EFB. There will possibly be a date code stamped on the top of the negative terminal, which can confirm age. AGM performance is superior to EFB and is possibly worth the extra cost - but it is even more important that new type is adapted (coded) into the vehicles BCM if changing type (any replacement battery should be adapted anyway)

Is your engine fitted with a normal dip stick - or is it one of these new 'wait until the low oil warning lights up'? - A terrible idea IMO.

I'm not sure I'd trust them much if it's common for them to hand over vehicles without oil even being checked - what else is being skipped? Is there any visible sign of this oil being burnt?

If the mileage was around 12k when purchased and you topped up with 1 litre of oil at 12,185, the oil level was presumably very low when vehicle was handed over - is that correct?

At 2 miles run, that would sound like an interrupted DPF regen.

Not sure if still applicable to current MIB Amundsen system, but in the MIB2 system, there is a 'check box' in the settings to provide a choice of three routes; Quickest, Shortest or 'Eco'

What was the mileage when you purchased the vehicle in May?

Not being a CI driver, I'm not sure that there is any visual indication on the instrument panel while a DPF regen is being performed - the only references I've heard of are elevated idle speeds, cooling fans running at high speed at engine switch off and unusual burning smells from exhaust system.

Are you seeing frequent DPF regenerations, and/or are regens often interrupted?

Hello, welcome to the forum. If travelling in heavy rail and the windscreen is fogging sufficiently to mask the interior camera, perhaps the driving conditions are not really suitable to be using cruise.

Which it should, if battery voltage is down to 12.2 as stated by OP.

I'd suggest checking the alternator output by testing the battery terminal voltage while the engine is running (should be something over 14 volts) - if that's ok, have the battery fully charged and tested again.

Was the battery BMS adaptation (coding) error corrected before or after the half-term holiday trip? Is the correct type of battery (EFB or AGM) fitted?

That sort of load can give some indication but is not usually high enough to be conclusive - a high load test will be in the region of 50 to 100 Amps minimum - measuring the battery terminal voltage while the engine is being cranked can give a fair idea of condition, but is limited to a short duration test unless the engine is prevented from starting.

At 12.2 volts, that 95% reading can only be battery Health - not SOC. Was the battery load tested under a high-rate load? Do you do a lot of relatively short runs? What is the battery terminal voltage with the engine running?

Another thought - is this happening when hitting deep standing water on one side?

It appears from OPs profile that this was originally a 1.8 L&K - and mentions in the post some 'Clutch' work with the conversion - but not what gearbox is currently fitted. If a manual box, I suspect a selector cable problem.

OP hasn't said yet whether or not the complete powertrain unit was swapped.

You haven't said whether your gearbox is Manual or DSG - What might be an issue is if the original gearbox (if retained AND DSG) is unable to handle the increased torque from the TT engine.

Have you had the vehicle scanned for any logged DTCs? Presume trailer is unbraked, therefore less than 750kg - is that correct?

Was it the complete engine and gearbox that was swapped? Unlikely that your gearbox issue has anything to do with the stated 'Nil Towing' capacity unless the engine (or gearbox) was overheating, which would also seen unlikely with such a small trailer. The 'Nil Towing' capacity will have simply been an Homologation requirement not fulfilled at the time of manufacture.

There is probably an option in the BCM to allow twin rear fog lights, as I believe that this is a standard requirement in some countries. If present, enabling this would allow both lamps to operate without flagging an error. I've always thought fitting a single rear fog light rather poor - apart from cost, the only positive factor I can see is minimising unnecessary rearward glare when lights are misused - which misuse should be policed a lot more.

Agree that rubber will not give an accurate reading, but there will be accessible metal parts that will give reasonably accurate ones.

Your lighting error will be because the fog light circuit is now sensing a higher current than expected (because of the extra lamp wired-in) Was the change entered into the can bus?