So after a year and half of owning my A4 the light finally came on, maybe it had something to do with my WOT for a minute the other day...anyhow. Went to autozone and got the following codes: P0118 and P0030. First one seems to be an $8 ECT sensor, and the next being I think O2 bank 1 sensor 1.....heater control circuit? Not too sure about the P0030 code. Now onto the DIY. I understand these cars have multiple O2 sensors on them, dunno which faulty one I have...and as for the ECT, where is that to replace? Lastly, To make sure these are both good codes I was thinking of resetting via battery to see if they come back...this a bad idea? I've had issues in the past with this and other cars; dealing with idle speed not resetting correctly etc. thanks for any input

 

also like to add, car is running OK; not too rich. MPG seems not effected much, and as for the temp gauge, thats working too...and not overheating etc.

 

B1S1 is the one right next to your air intake box.

If you pull your battery to reset you most likely will require a throttle valve adaptation

 

So, I ran down to see what the damage would be at the stealer for these fixes, and I am a little shocked. After they verified all the codes, I was told it would be just shy of 1G to get it all fixed up, and they'd need it over night for the exhaust to cool down. I figured 500 max but I was way off. I also looked at an extended warranty to boot just for kicks, those are also insane! Powertrain alone..almost 3k, goes way up from there. Are these sensors a huge PITA to replace or relatively easy for a DIY?? O2 sensor is before the cat correct?