indoor

I'm dealing with these codes too

It's not as simple as replace the cats.

First you have fix the issues that killed the cats(meaw, i.e. make sure no cats get into your exhaust pipes LOL Check for vacuum leaks(a pain in the butt if you don't have a smoke machine), yet I still have to try the propane method since the carb cleaner/vcds didn't do it for me. Then you either throw another maf at it or test/clean the one you have(more PIA with tests).

O2 sensor are new on mine, though i rushed into the problem and replaced them first...the old ones are still good though(ran some VCDS tests).

On top of all this crap, supposedly there is a dealer ecm software update that deals with this issue. I found it in the technical bulletins on eBahn(cd software service manual).

After all is good, though, I opted to get a new downpipe and cat together from RockAuto(about $300 shipped) which can be swapped in through a DIY. Mine is a 2.8L so this should do the trick: Instrux: DIY V6 Catalytic converter and O2 sensor replacement

Juniku

Shiiiiit

I have found multiple threads about P0430, and one solution is lambda spacer.
It does not repair the original problem, neither do ECU update.

bgross88

I have a 2003 A6 3.0, and was getting these codes: P0420 Catalyst System Efficiency Below Threshold (Bank 1)-- P0430 Catalyst System Efficiency Below Threshold (Bank 2).

Car ran fine, but I'm in PA so I needed to clear for emissions. Put spacers on each side, and those codes went away. However, I dorked up the Bank 1 O2 sensor when putting them on, and threw the code for the O2 sensor heater element(sorry, forget the code).

After looking at the 02 Sensors, I decided to replace all 4. Car has 110K and they were all original. Got mine thru Amazon, and saved a bunch of money.

After installing, I had NO codes, car passed inspection, and the engine light has been out for 3 weeks.

YMMV, but it would appear my issue was NOT the cats.

Airbag

yeah i had codes on my o2 sensors too .. fortunately for me it was heater element so the generic splice in Bosch worked great , been fine for allmost a year.

Juniku

Bank 1 have leak and that explanes why there is P1176, not P0420.


This downpipe with cat costs (MRSP) 1800USD in europe, so welding new part is 1st option.
Spacers arrives next week
P1176 P1177 O2 exhaust leak catalyst ASG 4B3254550X

indoor

I fixed mine temporarily with muffler putty. About $5 on amazon. Follow the instructions and it works. 6 months on this putty and still going it takes about 10 minutes on plastic ramps. Just make sure you get latex gloves and use your fingers to spread it all around the flex pipe(s). Since you're there putty the other flex pipe. There is enough to do two cars.
I did put some exhaust wrap over it also, but I don't know if it helps since I did a terrible job wrapping it.
Also bought some new flex sections but I'm waiting for the putty to fail before I worry about it

Airbag

the flex is down stream of the secondary O2 sensor .. really think that is your issue ?

johnkk

I believe flex is downstream from 1st sensor and upstream from 2nd(see pic of 2nd in thread). I think the spacer will fix the problem permanently or at least until the whole exhaust system starts to rust away.

Juniku

it looks like, i were wrong with this issue.
Leak before 2nd lambda in bank 1 messed up engine control totally
I thought it was not possible, all i read about his, said 2nd lambda is only for emission surveillance, tells if cat works or not...

Flex from bank 1 has been changed now.
I have driven ~700 miles now and there is no fault codes anymore, not even P0430 from bank 2! Lambda spacers have not been installed.
Fuel consumption has decreased, driving range has increased ~8%

Airbag

great work .. keep us up to speed on any new developments