2011_A3_20TDI

Hi all, I've got an issue with my interior blowers on a 2011 a3 2.0 TDI, the blowers seem to stop working if I set the both to "LO" and I get a fault code of 01273. If I remove the key and start again the blowers work. It seems to only happen if the engine is running. It happens if AC is on or not. Oddly if I start the car on "LO" it works fine and the air is cold, just if I go to HI and then back to LO it stops. I've replaced the blower motor and the module attached to it which I think is J126? with a brand new EIS motor and I'm still having the problem. I'm wondering if this is now the climatronic control unit itself but before I go down that route does anyone know of anything else I can try first? Also does the Climatronic control unit need coding to the car on a 2011? is there anything I need to be aware of trying to buy one? I'm using a cheap code reader called Carista, is there any value in getting a proper diagnosis with a specific Audi reader? Possibly related, the car has a feint light on the power steering occasionally which as far as I can tell is common on these cars but could it be something more sinister? Aside from the blower everything on the car works fine. Thanks all