To Cat or not to Cat!!

[wmccann]

Hi all,

Last year had a problem with my a4 Cab B6 (2003) 2.4 with Cylinder 5 misfiring. this went on for a few months and a lot of parts (some donor, some spurious) but no resolution so eventually replaced the engine (mine had 93,000 - "new" one had 55,000 miles - from 2005).

Anyway, long story short - problems resolved, car better then ever BUT MIL light recently has been coming on. when scanned I get error codes P0421 and P0431 - Catalytic convertor below efficiency.

The car has now hit 100k miles and was reading that the Lambda sensors should be replaced at this point so got 4 new Bosch universal ones. Installed at the weekend and all good. Fuel economy seems a bit better (probably too early to tell) but I am still getting the errors but no "check engine" light.

When I do the Readiness tests I can get all of them to pass but sometimes the Cat test comes back with Cat. bank 1(or 2 or both) not ok.

Using VCDS I have monitored the Lambda sensors and the signals from the front and rear sensors appears to be the same - i.e. the rear ones fluctuate as much as the front ones.

1) are my Cats shot?

2) Is it normal for both to go at the same time?

3) Since it appears it is not possible to get Audi ones any more (no longer made and no stock) what aftermarket ones are recommended?

Any help/comments would be appreciated,

thanks,

W.

[zollaf]

go to mot test station and get a cat test done. this will confirm if the cats are good or bad. make sure test is done with engine hot, a good 5-10 mile enthusiastic drive there will do it and then make sure its not allowed to cool down before being done.