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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E36 (1991 - 1999)

E36 (1991 - 1999)
The E36 chassis 3-Series BMW was a huge hit among driving enthusiasts from the first moment the car hit the pavement. The E36 won numerous awards over the years it was produced and is still a favorite of many BMW enthusiasts to this day! -- View the E36 Wiki

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  #1  
Old 05-09-2012, 02:01 PM
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OV2310 OV2310 is offline
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CEL p0420 code: catalyst system efficiency below threshold(bank 1)

I had this CEL on when I bought the car and I just wanted to find out what's the part number and where is it located? Is there a picture that shows me where it's at? I read that it's better to replace both o2 sensors so that the old one won't lag compared to the new one. I was looking at them on the pelican parts website but I just want to make sure I'm ordering the right one.
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  #2  
Old 05-09-2012, 07:11 PM
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drivinfaster drivinfaster is offline
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depending, you may need a cat, or you could have other issues that are affecting the performance.

this could include faulty post cat sensor(s) (the only thing these do is report on the cat, and do not affect performace), faulty maf, or unmetered air in the form of a vacuum leak (intake boot, usually a common failure), or faulty pcm.

you could throw parts at it, but the prices of these parts is such that guessing will be very expensive.

i suggest a trip to a certified emissions shop to get the cat tested to verify that it is, in fact, operating poorly and then dcide on a cat system for this.

and with new cats, i always suggest new o2 sensors. however, if during the tests the sensors check out ok, then you may not need to replace them.







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  #3  
Old 05-10-2012, 09:22 AM
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OV2310 OV2310 is offline
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Oooh man, I was scared about replacing the cats. I did replace my intake boot when I got it because it was ripped.
What was kind of weird was that my CEL read that code then I erased it and it didnt come back until one day I got the urge to floor it. It read me the same code p0420, I erased it again and it hasn't came back since then. Im scared it might be my upstream o2 sensors since those are the more important ones. It idles a little weird when its cold but nothing major. My rpms are correct but you can hear the idle going up and down a little when you get next to the muffler.
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Old 05-10-2012, 04:51 PM
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the primary o2 is for fuel trim only, the rear o2 is what will determine the efficiency of the cat. replacing the primary o2 will aid in better fuel control, and better emissions, but will not detrmine how effecient the cat is.



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Old 05-10-2012, 07:04 PM
tchavera tchavera is offline
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bad cat
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Old 05-11-2012, 10:41 AM
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Well I guess its time for a new cat system but not soon because im a little low on cash. Good excuse for a new exhaust . Im going to try to clean the o2s and the cat first though.
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Old 05-11-2012, 06:39 PM
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TRaV MaNN TRaV MaNN is offline
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I have the same problem. My plan is to switch the O2 sensors between each cat and see if the code follows the sensor. If it does, then a new sensor is all I need.


As for now, a code reader is all I need. Post cat's sensors just let you know if you will pass smog.
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Old 05-11-2012, 07:02 PM
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Quote:
Originally Posted by TRaV MaNN View Post
I have the same problem. My plan is to switch the O2 sensors between each cat and see if the code follows the sensor. If it does, then a new sensor is all I need.


As for now, a code reader is all I need. Post cat's sensors just let you know if you will pass smog.
Good idea!! Are the upstream and downstream sensors the same?
I would let you use mine if you were local to me. I order the usb to obd2 cable on ebay for $20 and has always worked for me. It came with the software too.
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Old 05-11-2012, 08:00 PM
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TRaV MaNN TRaV MaNN is offline
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All I've have heard regarding the O2 crap is that the post-cats are the same.

It's such a hit or miss though. It's either a $60 part of a $300 part. Need to find someone straight piping that would give their cat to me on the down low.
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