To really determine if your cats are no good. Try what I did
I removed my exhaust system underneath my BMW
because I was having a similar problem with those freakin cat codes.
After I removed the exhaust pipes I got a flash lite and looked up into the rear cat and to my surprise it was plugged but the honey comb shape was ripped in two places and the car ran great.
I could not see into the front cat because the pipe is to long and curved but good luck.
Normally only one cat always goes bad.
My recommendation is to buy the original
OEM CATS from the BMW DEALERSHIP.
Because if you buy them out of state your taking a big risk.
But it's your decision.
I know the cat are expensive from the dealership but you'll say time and money in the long run
I got a discount from the dealership he trimmed about 150.00 bucks
Pa if you buy after market cat the CEL will still illuminate.
Last edited by Adolf; 06-06-2012 at 10:30 PM.