e39 540i Lacks Power, sends codes p0150, p0155 and p0170
 

My 2000 540i sport 6 speed has been throwing codes, doesn't have the power that it should and is not running as smoothly as it should. A while back it was setting P0170 and P1340 codes, so after a bit of forum searching I decided to replace the pre-cat O2 sensors and the cam position sensors. I replaced the O2 sensors first and the difference was nothing short of amazing! Smooth, powerful, ran like new.

Unfortunately this lasted only for about 50 miles and it slowly started degrading again. By this time the cam sensors came and I replaced those, but there was no improvement except that I have not seen the P1340 code since, but still get P0170 every couple of weeks or so. A couple thousand miles later and now I am getting P0150 and P0155. These both refer to the O2 sensors.

Could my new O2 sensor(s) be bad? Any ideas? I had a taste of true 540i performance for 50 miles and I want it back! Help!

Thanks,
Rich

Could be a vacuum leak or your cat has had it. Do you know what the fuel trims are doing?

Other than the P0170 bank 1 fuel trim malfunction code, I don't know what the trims are doing. I only have a code reader, not an analyzer. How can I tell if the cats are bad? I was thinking about swapping the O2 sensors and see if the 150 code moves to the other side, but the odd thing is that it ran so well for a short period of time after changing the sensors.

Nothing odd about running better w/new sensors. However the reads may have slowed or stopped (could have gotten clogged with carbon soot) because the cat may have died. You need to be able to see what the O2's are doing. The front ones should be switching and the rear ones should be steady.

Try the swap and see what happens. If it does the same thing you may have a toasted cat, if the code moves you may have a bad sensor.

Otherwise it might be time to take it in and have it analyzed by a BMW guy.