Mysterious Brake Pad Warning

[M-A8]

Hello
I didn't want to hijack 1781cc's thread further so here is a separate thread about my mysterious brake pad warning I mentioned the other day.

Don't know if this is just coincident or it has anything to do with it, but in September when car went for a full and comprehensive service inc. gearbox service, all the fluids, wheel bearings etc, I've had also rear pads replaced as the rear suspension was completely stripped down and rear pads were low anyway.
Front pads hasn't been touched, but the brake fluid has been changed.

I can't remember exactly if it was week or two or three since all the work, hence me thinking it's just the coincident as it wasn't straight after, when I got the first brake pad warning light on the dash.

It has been like that since, originally I've scanned the [03] ABS ECU for faults, but there was non. Then in 1781cc's thread it has been suggested to also look in [53] Parking Brake ECU. It took a good week or so for the fault to come back (I didn't drive much recently anyway), but it finally did.

For a second today I thought this could be related to ESP because the fault came on after getting the rear end a bit happy which happened quiet often in past few weeks due to wet conditions, but I've ruled that out on basis that fault was coming on even on motorways driving steady and in dry conditions in October and November.

I did scan both ECUs while fault was still flashing on the dash and there was nothing, absolutely no faults whatsoever.
See attached photos.

Any clue what this might be??

I haven't get to the stage of replacing the EPB ECU yet as it was suggested few days ago.

Thanks guys