Im trying to do some oxygen sensor work and I need to know which wire does what on the 1998 740il. Basically which color corresponds to what function on the post cat O2 Sensors
Signal
Ground
12v
Heater
Thanks for any help

If someone can get me this information from there bentley manual I would greatly appreciate it.
Thank You

Did the wire get cut somehow? I mean, out of curiosity, what are you doing?

Installing an O2 simulator, I am not willing to pay $2000 for cataytic converters to put on a car thats not worth more than $9000. I don't plan on keeping the car much longer so I replaced it with an aftermarket cat and just want to get rid of the CEL.

That's interesting.

I'd love to see some pictures.

Sorry no pics as my camera is currently mia.
Anyway I bought the dual output sensor from www.o2simulator.com.
Seems to be working flawlessly, I will post back in a few days and let you guys know the final result.
This could be an alternative to buying expensive factory cats. You can put on some magnaflow catalytic converters, order this simulator and be on your way for well under $300.

Dang it, this sounds awesome! You've got to borrow someone's camera so we can see this.

been a day and put about 150 miles on the car. No cel yet and the car seems to run smoother, I had a slight hesitation before and oddly enough the mpg has gone up just a tad bit although I believe the secondary o2 sensors have nothing to do with a/f ratios. Either way I would reccomend this set up to anyone with failing cats who don't want to shell out $2000+ for new ones.

Guys have run these for years on the Turbo Buicks and Lt1, Ls1 F-bodies, so they must work okay.

Replacing your bad cats WILL increase power and mileage because you unclog and free up the exhaust path. Are you saying you have a simulator on both of your post-cat O2 connections?

Yes I have it on both of my post cat o2 sensors. My cats are not bad, they are brand new, just not factory. And everyone on here knows that anything other than a factory cat will set off the cel. Even if these aftermarket ones last me two years before I need to replace them I would graciously do that then spend $2000+ just in parts for factory replacements.
My car has 110k miles on it and I know it's not worth more then $8500-9500 on it's est day even though it is mint. It would be ridiculous to spend 20% of it's value in a repair that will not add any value to the car.

I agree. I know you have new cats. I was responding to a comment that new cats lend more power and performance a car.

As for your install, that is great... I will probably go with aftermarket when mine come due. I've heard a lot of other guys replacing their cats with Magnaflows or some other aftermarket item and not having any CEL issues. It is essential to make sure the old 02 sensors ARE replaced after the new cats are installed though.

oddly enough when i first replaced my cats i got no cel for about a month. THen it came on, I then replaced all 4 o2's and the light stayed off for another 2 weeks. Shortly thereafter I got the cel again for inefficient catalyst.

The 2 rear O2's usually only need the simulators, you are right about the rear O2 not having any input for the AFR. Your problem with the CEL is somewhat common after cats (aftermarket) being changes (usually set rear O2 sensor codes). Changing fuel companies further contributes to the problem as the fuel additives, octane rating differ slightly. Try to stick to the same oil companies for awhile or until the system fully recalibrates. The system will continue to monitor the AFR and rechecks the calibration on restarts. So when the CEL light is cleared the whole process of recalibration starts up again. Usually once the system get a little more usage the block learn #'s get evened out and the system learns the settings and usually the CEL will go out for good. However, this isn't always the case, that's when the simulators give u the peace of mind..

Forgive my ignorance...Does an O2 simulator replace the real O2 sensor and makes the engine computer think that it has healthy (O2) sensors and cats?