greg12m3

So every month for the past few months I have had a problem with my car. Last month it was my alternator and last night ensured I will have a problem this month as my CEL came on.

Scanned and got, P0422 & P0432, and a message " main catalyst efficeny below threshold"

My exhaust is set up with high flow cats in place of the primary and then straight pipes back to the oem muffler. I don't know if the cats are ceramic or metallic but I have a feeling they are ceramic which maybe the problem.

Any input is appreciated and I plan on going to the dealer and my indie,thanks!

CTE55AMG

I'd say it is oxygen sensors. That is what happened on my 530i a few years ago. I thought I needed a new cat, but the O2 sensors were shot and were giving the car a bad reading. I changed the O2 sensors and the codes never reappeared.

greg12m3

I thought that a code would come specifically from the O2 sensors not just a code stating the fail of the cats. Thanks though, I'm going to mercedes today to have them scan everything and hopefully they will be able to pin point which 02 sensor or what not. But if all else fails i will just through some straight pipes on.

ProjectC55

You need to use spacers for the O2 sensors. My car has the same problem right now,I just have not had the time to address the problem. My buddy with his SRT8 also had the issue after upgrading his exh and it was solved by using spacers.

ProjectC55

This is why! I have the same issue as well.

greg12m3

Spacers? I don't understand?

greg12m3

What are spacers?

greg12m3

So the other night while out on a drive my CEL turned off.. I'm not complaining but I would like to know why? anyways I'm using all of this as an excuse to put on an x-pipe and because of that I'll have an opportunity to look at the cats.

ProjectC55

You would add a spacer or actually weld a spacer to the mounting point of where you would screw in your O2 sensor. google "spacer for O2 sensor" and you'll find out all you need to know. or even try looking it up here on MBworld.

fangtl

I think the more common term is anti-foulers, it basically looks like this and can be purchased at any auto parts storefront

greg12m3

How do these anti foulers work? thanks! I'm going to be doing this as soon as my shop can take my car. Also, When the o2 sensors aren't working or are reading errors, does that affect how the car drives? again thanks!

fangtl

as one of the previous posts mentioned, it's basically a spacer, the o2 sensor is taking a reading from the spacer and not directly from the aftermarket cat/test pipe.