Well I have ask that to dealers and the cost is $ 192 bosch sensor's there are 4 though (audi has 4 sensors), so you might need to know wich to replace, before or after catalitic, extra tip, there is a universal sensor for audi a6 they are cheaper, $ 70 dollar but they come without the coil plug you got to take the old plug and put it together with this new sensor will be the same but cheaper. Autozone or napa carry them, and now that I think we have the same problem can you tell mewhat is your car doing, I mean what is wrong with the car run normally? Answer me please
October, 18, 2007 AT 12:29 PM
I ended up not changing them. Today I went to a diffrent service for state inspection and the car failed the emission test. Due to OBDII diagnostic trouble codes p0421, p0441 and p0431. And the guy told me to change the catalytic converter 4 of them each 400$. Does any one has any experiance with this problem?
February, 17, 2008 AT 10:02 PM
On my A6 Avant, I have been getting these same codes since at least 80K in 2004. P0421 (Pri Cat Bank 1), P0431 (Pri Cat Bank 2), and P1423 (secondary air flow too low bank 1) always show up 1 or 2 days after being cleared.
I can guarandamtee you these cats did not go bad at 80K.
How to know? I always knew those emissions tests in Denver would be good for something. In 2004 at 66K, my hydrocarbons were 0.07 gm/mi and NOx was 0.2 gm/mi. In 2006, at 136K HC were 0.13 gm/mi an NOx 0.3 gm/mi. Pass/fail cutpoints are 1.2 for HC and 3.0 for NOx. This car is pretty darn clean from an emissions standpoint.
If the cat was shot, HC would be much higher, trust me, people I know who have had bad cats have failed the emissions test hands down. Even if my cat is bad, why would I replace it if my car runs that clean? That makes no sense.
I need another emissions test this year (177K) so will do that before taking to my mechanic this week. I will try to have him do a pre- post- cat temperature reading.
The fuel economy on this car has always ranged from 20-22 mpg, so I don't believe it is an O2 sensor. I believe it is a secondary air leak issue that is of very minor concern (except for that damn CEL/MIL). Hope to have a diagnostic on that this week.