Hi there,

I have a 2011 120i coupe and recently the engine warning light came on. However when the car was left to stand it went away and I drove it as normal for another week. However, the light came back on and again, after a day or two the light went off. I've taken it into a garage to have the fault codes checked and they said that there were 9 codes that showed up. On the paperwork they've given me, four are mentioned:

2af9 - Nox sensor
30cl - oil pressure regulation
29f4 - CAT system efficiency below threshold bank 1
29f5 - CAT system efficiency below threshold bank 2

He's flushed the system with an additive solution which he said might resolve the issue, but to take it back if the light comes back on again (which I have a feeling it will given that it's come and gone over the last few weeks).

Would anybody have any idea what type of problem might be causing this, and more importantly whether it's likely to be an expensive fix.

I'd be really grateful for any advice anyone can give me. The car's driving fine, it's not misfired and lost power at any point and it mainly does motorway driving with a little bit of stop start at the beginning and end of journeys. Would anyone be able to help?