AUDI BUSH

Had the car a week A4 Auto, Avant, 1.9TDI SE, my dad has owned it for 8 years full Audi service etc etc mint through out never been thrashed etc etc. ESP light came on for my dad a month or so ago but went out, since then it has come on a lot but gone off no noticeable issues. Last night it went mad and flashed a lot and the car slowed down as if it was controlling it? Put my foot on the brake and the ABS went off briefly (as if speed sensor fault) the vibration stopped and the ESP light stayed on without flashing. Car drove fine for the rest of the trip home no more lights, no abs or light, nothing just solid ESP light. Scanned it today with code reader and I have 01826 Steering angle sensor, only a cheap code reader so I can go deeper but no other faults/codes. Also checked the wheel speed sensors, in particular the ns front which my dad said had loads of crud pressure washed from it just before he first saw the light a few months ago. Nothing, all clean. Light came back on and off on the 5 mile trip home? When light is out it does appear that it comes on more regularly when going left rather than right, also picked up on the net somewhere that if the battery goes flat it can set off the Steering angle sensor? Cruise control works fine as well. Help and input greatly appreciated, got tools and years of spannering behind me just dont want to go off in the wrong direction :)

Hi all Got my dads mint 53 plate A4 Avant 1.9TDI Auto as a present the other week. One slight issue which has prompted me to join up and share the love, dreaded ESP light / 01826 code.....