Question about 1996 BMW 7 Series

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BMW 740iL 1996 OBD fault codes p1036, p0156 or BMW 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).which are OBD codes p0136 & p0156. 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. Did he miss something doing continuity checks?

I have also brought it to the local BMW dealer (rip-off) 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 was that both aftermarket cats were defective, and the result is fouled rear monitoring (post cat) O2 sensors. In his words I need new BMW cats (aftermarkets don't work well), and of course new O2 sensors. I don't trust them, definitely won't go back. I realize that there is a warranty on the cats, but I was hoping for any ideas 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 the cats are shot - also the O2sensors??? I still believe it is an electrical circuit problem, why can't they find it? I have yet again someone doing a continuity test today and anxiusly await the outcome. Comments welcome!

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  • Anonymous Mar 17, 2014

    replaced both before cat sensors twice, swapped wiring still bank 1 sensor 1 fault comes up right away.



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Sorry but in this case the dealer is correct,ONLY oe cats will solve this problem, have worked on dozens of the cars no aftermarket cat i've seen has worked. you can chase this problem all over but it will still go back to the cats ,sorry no better answer

Posted on May 21, 2009


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