If both post-cat O2 sensors have been replaced, it's the cat. Replace both, as the other one will fail soon, too. Magnaflow does not offer a cat for your car. Unless you can find a universal fit cat, you'll be at the mercy of the dealer.
Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.
Last edited by edjack; 11-29-2011 at 02:00 PM.