Audi for life 1987

P0431 is warmup catalyst efficiency below threshold bank 2 cat or O2 sensor ? Any one have the same problem before?

lyleswk

No experience with it, but from reading other forums, here are the possibilities:

1- Catalytic converter defective (failure possibly due to #2, 3, or 4)
2- Engine misfire or running condition
3- Large vacuum leak
4- Engine oil leakage into exhause-valve guide seals, piston rings.

2 would be obvious. You should be able to eliminate 4 assuming you don't have oil consumption issues. I think you would notice 3 in the way the car performs. 4 would only be identified if you have to have an emission test in your area.

Just food for thought.

Pete@ECSTuning

^^^ Above is a great post, I will just add that B2 is driver's side cat.