Below threshhold cylinders 4-6...o2 sensor?

[cmb516]

I'm getting the below threshold code but only for cylinders 4-6. Does this sound like an o2 sensor, if so pre or post cat? Or are the cats on the way out. It's a 1998 m3 with 82000 miles so I would lean towards an o2 sensor. Let me know what you guys think, thanks.

[LuxoM3]

What are you using to get the "below threshold code?"

If it's the Peake Tool, it will tell you if it's the O2 Sensor :)

[cmb516]

I am using a peake tool and that is the only code I am getting. I have been reading around and seen that this could be because of a sluggish O2 sensor. I have read to replace the pre-cat O2 sensor in some places while other places say it is the post cat sensor. Just wanted to see which one you guys thought it would be before Itear into it.

[LuxoM3]

Are you reading this?...
"Catalyst efficiency below threshold, Cyl #1-3"

If so, I'm reading it as your O2 sensor is picking up that your cat isn't working right. (As your ECU would use the AFTER car sensor to measure efficiency).

And then again It could be the O2... maybe.

In all honesty, the O2 sensors on the OBD2 cars all tend to fail within 10k miles of each other. (My precut ones started dying at like 45k and 50k). If you've got over 75k miles it's time to change them all anyway. But they aren't cheap, like $115/piece last I remember, and you have 4 of them (2 sets of down pipes, 2 sets of O2 sensors before and after the cat).

If it isn't the O2s, it's the cats... which don't work very very past 120k miles.

What state are you in? If emissions aren't an issue, I'd go with the O2 sensors first. if you still get the CE light, weigh your emissions laws into the decision. Cats are REALLY pricey to replace. If you aren't in a SMOG crazy state, you can get new Magnaflows welded in for $400 parts/labor - and probably pick up some power too.

[cmb516]

Are you reading this?...
"Catalyst efficiency below threshold, Cyl #1-3"

If so, I'm reading it as your O2 sensor is picking up that your cat isn't working right. (As your ECU would use the AFTER car sensor to measure efficiency).

And then again It could be the O2... maybe.

In all honesty, the O2 sensors on the OBD2 cars all tend to fail within 10k miles of each other. (My precut ones started dying at like 45k and 50k). If you've got over 75k miles it's time to change them all anyway. But they aren't cheap, like $115/piece last I remember, and you have 4 of them (2 sets of down pipes, 2 sets of O2 sensors before and after the cat).

If it isn't the O2s, it's the cats... which don't work very very past 120k miles.

What state are you in? If emissions aren't an issue, I'd go with the O2 sensors first. if you still get the CE light, weigh your emissions laws into the decision. Cats are REALLY pricey to replace. If you aren't in a SMOG crazy state, you can get new Magnaflows welded in for $400 parts/labor - and probably pick up some power too.

I am getting the code 16.EA

Which returns:

"Catalyst efficiency below threshold, Cyl #4-6"

And that is the only code that is read from my peake reader.

I just moved to Maryland and I think they do have emissions here. I hope that the cat is not gone and it's just the o2 sensors. I guess I'll go ahead and get some o2 sensors and see if that does the trick. I just got the car a month ago and I believe they are the original sensors.

[NAZ1998BMWM3]

It's probably your rotor splint.

[cmb516]

It's probably your rotor splint.

What is the rotor splint?