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7 Series (E23, E32, E38, E65, E66)General discussion and technical help for all year 7 series cars.
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Your Ride: BMW 740iL 1996
740iL Help, BMW fault codes 12 & 20
My 740iL has DEC aftermarket direct fit replaement cats installed Jan 2008. The four Bosch oem O2 sensors were replaced at the same time which is only 2200 miles ago. The car ran fine for a year but I am now getting BMW fault codes 12 & 20 (post cat sensors bank 1 & 2). I should note that my regular mechanic checked fuel trims and wiring continuity,installed new platinum plugs etc. and all is running really well - there is no fault codes from the front sensors.
I have also brought it to the local BMW dealer who says he reprogrammed the DME, ran a continuity test on the O2 sensor wiring which was OK, and swapped out the post cat sensors for testing. His conclusion that both aftermarket cats were defective, and the result is fouled (burned) rear monitoring O2 sensors. In his words I need new BMW cats (aftermarkets don't work well), and of course new O2 sensors. I realize that there is a warranty on the cats, but I was hoping for any ideas from the community before I make a claim. I know DEC ships an awful lot of cats, and I am having a hard time believing 2200 miles in 15 months and they are shot - also the O2sensors!!!!
Last edited by EuroSpace; 05-13-2009 at 12:55 PM..