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Old 07-25-2008, 09:52 AM   #1
security6
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P0430 P0420 - Catalyst inefficiency - do I have to replace cats?

I have been getting P0420 and P0430 (not always at the same time) about once a month for the last 4 months. This past week, I have gotten the P0430 code 3 times. My car runs great. Acceleration is good, no rattles from underneath, no indication that anything is wrong except for the CEL. I replaced the post-cat oxygen sensor on bank 2 about 5 months ago with a new Bosch sensor. The precat sensors look good, but I don't know how old they are.

I'm thinking of doing the spark plug nonfouler "mod" on the post-cat oxygen sensors just to stop the CEL from coming on. Any reason (besides excess pollution) why I shouldn't do this? Will it have any long term effect on my car?

A little extra info to head-off the inevitable questions:

My next smog check isn't until March 2010, so I'm good for a while. Also, they don't use a sniffer here, just check for OBD readiness.

Car is a 2001 330i w/ 113k miles. I've owned it about 6 months. Last February I had some vacuum leaks which have been fixed for a while. I replaced the spark plugs, VANOS seals, and valve cover gasket about 1.5 months ago, as preventative maintenance.
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Old 07-25-2008, 10:02 AM   #2
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the cats are built into your headers...

maybe its time to change the 2 post cat sensors..
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Old 07-25-2008, 10:19 AM   #3
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the cats are built into your headers...

maybe its time to change the 2 post cat sensors..
Hmm....not sure I understand why you think changing the post-cat O2 sensors will do anything. I changed the post-cat sensor on bank 2 last February. I've only driven 4000 miles or so since then. Do oxygen sensors usually go bad that quickly? If the oxygen sensor was bad, wouldn't it throw a different code than p0430? Am I missing something here?
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Old 07-25-2008, 10:23 AM   #4
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there are 2 pre and 2 post.. you only changed one?
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Old 07-25-2008, 10:43 AM   #5
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there are 2 pre and 2 post.. you only changed one?


Yep. I only changed bank 2 post-cat because that was the only sensor I got a code for (heater circuit on the sensor was bad). The sensor was replaced with a Bosch sensor designed for BMWs (i.e. I didn't have to splice any wires).

The 2 pre-cat sensors look fairly new, but I don't know for sure how old they are since they were there when I bought the car 6 months ago. I'm almost certain the post-cat O2 sensor on bank 1 is original.

Just to be clear, here is the timeline:
Jan 2008 - purchased car
Feb 2008 - replaced bank 2 post-cat O2 sensor
April 2008 to July 2008 - p0420 (bank 1) and p0430 (bank 2) codes appear about once a month. Sometimes both would come up, and sometimes only one would come up.
Week of July 20, 2008 - p0430 code (bank 2) is appearing every 2 or 3 days.
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Old 07-25-2008, 12:28 PM   #6
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I would change the pre-cats. A bad pre-cats may throw a code for the post-cat, not because the post is bad, but the emission is not normal.
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Old 07-25-2008, 12:43 PM   #7
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i have a peake tool.. bit starnge with looking up all the f32 c23 codes but it shows clearly..


and maybe...

just maybe.. do you know if these headers are stock? you should have two resonators that kinda look like cats but theyre not
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Old 07-25-2008, 01:23 PM   #8
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i have a peake tool.. bit starnge with looking up all the f32 c23 codes but it shows clearly..


and maybe...

just maybe.. do you know if these headers are stock? you should have two resonators that kinda look like cats but theyre not
Not sure what you mean by the red sentence. I get the codes from a standard OBDII reader, not a Peake tool.

I'm sure the headers are stock. They have the BMW logo stamped on them.

Some interesting thoughts. I've never heard of bad pre-cat O2 sensors setting off a cat ineffiency code, because there are codes for bad O2 sensors.

Perhaps I need to get a scan-tool to hook up the computer to see what the O2 sensors are reading. On the other hand, it would be cheaper to do the spark plug non-fouler "mod."
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Old 07-25-2008, 03:06 PM   #9
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if the cats are bad its time to get headers and software or headers and race cats
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Old 07-25-2008, 03:52 PM   #10
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change ur cats
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Old 07-25-2008, 04:03 PM   #11
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the regualr obd2 scanner will show oxygen sensor codes it as heater circuit and the bank number..

a peake scan tool will give you a code like 0A

which then explains EXACTLY what it is..





its usually the pre-cats that go out first.

and guys.. the cats ARE the headers.built in ..
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Old 07-25-2008, 05:34 PM   #12
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Most OBDII scanners will also show manufacturer specific codes (e.g. P1XXX), but the description might be off. However, the Bently manual gives descriptions for all the codes (regular and manufacturer specific).

The Peake tool isn't giving you any more information than an OBDII scanner (one that can read manufacturer specific codes at least). You just have to be careful not to trust the OBDII scanner description - double check it in the Bently manual.

As an example:

OBDII code I got was p0430 - catalyst inefficiency bank 2

If you hooked up a PEAKE tool you would get 06-2D. Then you would look it up in their book and see that it says catalyst efficiency, cyl 5-6. (The Peake manual here is wrong. It says there is a code for cylinders 1-4, and a different code for 5-6. It should say cylinders 1-3, and cylinders 4-6)

Last edited by security6; 07-25-2008 at 05:40 PM. Reason: Add an example
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Old 07-25-2008, 09:05 PM   #13
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Take a look at your O2 sensor values for that bank, I have seen a couple of instances where lazy sensors that are just above threshold set cat efficiency codes, but you had the sensors replaced right? there is a catalyst efficiency test that I perform but it involves two people, scan tool, and a 15 min test drive. Cats are quite expensive to replace so take it to someone who can give you a definitive answer before replacement.
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Old 07-26-2008, 06:41 AM   #14
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Thanks for the help. I ordered a scan tool that will give me live readings from the individual O2 sensors, so I guess I need to wait to get it before I do anything else. Luckily, I have a long time before I need to get emissions done on my car.
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