Engine code problems. Please help...

[Dazzlindoer]

I had a bad o2 sensor (the one after the CAT). The code was showing this and the voltage signal confirmed it. I drove it for about a month with it in this condition. After replacing the sensor the engine light came back on after aprox 10km. Checked codes again and it is saying that there is a fuel trim problem and 02 sensor before the CAT. The codes were reset and the engine was monitored while driving, and a the mass air had a little hick-up at highway speed causing a code to store in bank 2 but not causing the check engine light to appear. The engine light was coming on when the o2 and catilitic efficiency codes appeared.

I don't want to keep replacing $300 o2 sensors or $1000+ parts (cat or mass air sensor) if the root problem can't be found.

Any help please and thank you.

[Big Al]

What codes are being triggered? It may be related to the MAF or vacum hoses. I recently had the P0170 and P0173 codes. I am going to try and clean my MAF, if that doesn't work then may need to replace it. Search the board with the code and you may get some answers.

[Dazzlindoer]

I asked my mechanic and he said the codes are 234 cat efficiency bank 2 deminished. This code is coming up on a regular basis. Code 226 fuel trim problem has also been logged. He uses a Snap-On scanner which gives the BMW codes, not a genearic code.

[The Cleaner]

If you have no Vac leaks the MAF is probably the starting point. The o2 code is probably a result of the fuel trim.