Hi all iv not long bought a Superb estate 2.0tdi 2015 with 54000 miles on the clock  great car but has problems probably why it got sold i soon found out the battery was on its way out stop start not working it would take a full charge off the car to 12.6 then drop to 12.2v so i bought a new AGM battery coded it to the car now stop start works ok. then when its frosty heated windows would switch off this it to do with the battery management so i checked voltage at the battery it was 12.1 volts running idle speed was 1000rpm a blip of the throttle volts jumped to 14.2v i have to do this every time or it won't charge a VCDS scan gives fault generator regulator fault 02252 plugging a voltage meter it to display voltage I'm getting 14.2v all the time whilst driving it will only charge the battery too 84% and amps drop to 2 after a while this is normal i think bar the constant 14.2 volts so am thinking the regulator is faulty or am i missing something 

Hi Cybrshot, welcome to the forum. The correct charging voltage for a AGM battery is approx. 14.7 VDC - but the battery monitoring module (BCM) will normally only allow the battery to charge to approx. 75-80% of full charge to allow sufficient capacity in the battery for regenerative charging under certain circumstances (this is where the 'micro-hybrid' part comes into play) - 14.2 VDC is around what I see on my Octavia with the hood up. This does mean that you will usually find the battery below full charge. If the 02252 regulator fault does not clear, it may be that the regulator is faulty - or it may be that the fault wasn't reset previously although my understanding is that this would normally reset itself once the battery had been replaced. Have you attempted to reset this fault? Is your engine idle-stop working correctly now? Does the screen clear before switching off?

You should have a look at this thread, it sounds like a similar issue:

 

yes stop start is now working ok it will also work with a cold engine sometimes 

11 hours ago, Warrior193 said:

 The battery monitoring module (BCM) will normally only allow the battery to charge to approx. 75-80% of full charge to allow sufficient capacity in the battery for regenerative charging under certain circumstances (this is where the 'micro-hybrid' part comes into play)

This is very interesting, and has cleared up a few doubts i had in my head about a new battery I have installed and coded. Thanks.

i tested the plug on the alternator that has a single wire and it was 8v to 8.5 v am not sure if this is ok  my stop start has now stoped working with a warning on the dash to say its faulty the car got a 30 mile run yesterday and the voltage never dropped below 14.2v unless i switch on front and rear screens it will drop to 13.5v .battery reading 12.5v next morning outside temp -2

 

The single wire on your alternator is a LIN data connection, so I wouldn't expect its voltage to be a useful measurement.

The charging voltage being a fixed 14.2 suggests that the alternator has defaulted to 'traditional' behaviour which may be consistent with a disconnection of this LIN data stream at either alternator or battery management module (near batt negative post). Such a disconnection will result in start/stop being inhibited.

 

The overnight voltage suggests that the battery is pretty healthy though.