DIY Catalyst/O2 Sensor Replacement

[Bisonhead]

Originally Posted by mannyo

IIRC The cat below efficiency error starts cropping up when the cat is 94% efficient and triggers the engine light. Even with the light on and the fault code the car should breeze through the MOT. Check the air filter to make sure its not clogged up.

Will do, thanks. It is an ex-london car so probably needs a good de-smog anyway

[daviesbike]

I had the same fault on my 4.2 LWB and the W12 once and it is exactly that when it drops to below 94% efficiency it triggers the emissions light to come on. Very annoying when you think to drop 6% efficient is enough to trigger the light..

My solution was acctually cataclean ... then I discovered its no more than body shop paint cellulose thinners put in a bottle and sold at 8 pounds odd..

So I ended up buying a gallon of thinners from a body shop ..

I put 1L of thinners into a quater of a tank of fuel

And went for a good blast for about 1 hour lots of 2k cruising and then 5k manual gear from 40mph to 60 70 .. so its under load ..

Do this untill you have literally 10 miles left on the dis

Then go and fill up with half a tank or so ..

Then vag com it clear fault codes and it didnt come back again..

The thinners clears all the build up of laquers in the cats

After so many stops and starts maybe 10 from memory the cel light will go out with out vag com .. but if you have it just use it.

Saves a lot of money and can be repeated before mot for emissions ect ... I actually used red x injector cleaner after doing this just to make sure the rubbers are all lubed up and not dry..

Ive done this on 3 of my A8s now that had the same fault and it worked every time apart from once when I had to repeat and do it twice .. depends how caked up the cats are I guess

[Bisonhead]

Originally Posted by daviesbike

I had the same fault on my 4.2 LWB and the W12 once and it is exactly that when it drops to below 94% efficiency it triggers the emissions light to come on. Very annoying when you think to drop 6% efficient is enough to trigger the light..

My solution was acctually cataclean ... then I discovered its no more than body shop paint cellulose thinners put in a bottle and sold at 8 pounds odd..

So I ended up buying a gallon of thinners from a body shop ..

I put 1L of thinners into a quater of a tank of fuel

And went for a good blast for about 1 hour lots of 2k cruising and then 5k manual gear from 40mph to 60 70 .. so its under load ..

Do this untill you have literally 10 miles left on the dis

Then go and fill up with half a tank or so ..

Then vag com it clear fault codes and it didnt come back again..

The thinners clears all the build up of laquers in the cats

After so many stops and starts maybe 10 from memory the cel light will go out with out vag com .. but if you have it just use it.

Saves a lot of money and can be repeated before mot for emissions ect ... I actually used red x injector cleaner after doing this just to make sure the rubbers are all lubed up and not dry..

Ive done this on 3 of my A8s now that had the same fault and it worked every time apart from once when I had to repeat and do it twice .. depends how caked up the cats are I guess

Glad to hear Im not alone, I will give this a go before getting my hands properly dirty. Will post the results when done

[daviesbike]

No problem let us know how you get on

This is where I first seen it

Watch "Fixing Bad Catalytic Converters With Inefficien…" on YouTube
Fixing Bad Catalytic Converters With Inefficien…: http://youtu.be/5icTmYItwiE


Its laquer thinners he used a gallon for 150 miles ...
I used 1 liter at a time until it was sorted but if you do a long drive it would clean better I guess