Seems to be common but struggling to point cause?

I had the wheels refurbed and the serpentine belt and tensioner replaced on my a4 2.0tdi. On the way home the traction control light came on. Now it comes on every time but not for a few miles. The car also had tghe red brake light flash up at start up but only when cold.

I've changed the battery and that has fixed the red brake light issue. But esp light still coming on.

Fault codes include;

17911 Load signal from alternatot
18265 Load signal error message from ecu

Any ideas? I have searched and found various theories. The car is a bit lumpy on idle (MAF??)