fault code P0420 - BMW Forum - BimmerWerkz.com
3-Series (E36) Chat relating to the BMW 3-Series from 1992-1999. Autodoodad Specific models include: BMW 316i, BMW 318i, BMW 318iS/ti, BMW 320, BMW 323, BMW 320, BMW 324, BMW 325, BMW 328.

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#1 (permalink) Old 05-08-2004, 01:52 AM
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got my check engine light on so i had it scanned. it showed a PO420 - catalyst effeciency low (bank 1).

according to the OBD II scanner manual, possible causes are:

1. catalytic converter defective / failure possible due to #2,3, or 4

2. engine misfire on running condition

3. large vacuum leak

4. engine oil leakage into exhaust valve, guide seals or piston rings

5. refer to AZ commercial preferred customer.

my questions:

a) if anyone can please tell me in plain language what all these mumbo jumbo mean?

B) i believe there are two 02 sensors on my 96 318i. need i replace both at the same time? or at least is it desirable to do so?

c) will i have to go to a dealer to have the check engine light reset?


any help is greatly appreciated.
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#2 (permalink) Old 05-08-2004, 02:16 AM
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That code is usually set by an O2 sensor that is not working properly. If you can wait till Monday I can find out which O2 sensor should be replaced, before or after the cat.
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#3 (permalink) Old 05-08-2004, 03:48 AM
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thanks...

i'll be glad to know.... so then i would not have to incur needless spending.

any chance though that it is my cat converter that is damaged? if so, what are the signs that it needs changing?
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#4 (permalink) Old 05-08-2004, 03:57 AM
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Unless it is broken inside the only way to tell if a cat is bad is to hook up your car to a 5 gas machine and read what comes out of the tail pipe. 80% of the time replacing the bad O2 will solve your problem but I've seen cases where the cat has gone bad. How many miles are on the car?
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#5 (permalink) Old 05-08-2004, 04:19 AM
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got 113k on it. bought it when it was 109k few months back
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#6 (permalink) Old 05-08-2004, 04:48 PM
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has anyone had this before?
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#7 (permalink) Old 05-08-2004, 05:26 PM
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Unfortunately I have no engine warning light in my dash

Maybe I have the same problem without knowing that.

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#8 (permalink) Old 05-08-2004, 05:36 PM
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Could be merely an o2 sensor, but it could be the cat as well. Have you noticed a smell of rotten eggs after driving?

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#9 (permalink) Old 05-08-2004, 05:48 PM
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no, none of those smell....
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#10 (permalink) Old 05-08-2004, 06:47 PM
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Quote:
Originally posted by dutchbmw@May 8 2004, 05:06 PM
Unfortunately I have no engine warning light in my dash...
Really? That's the first thing I check for when I test drive a car. It should come on when the ingnition is turned and then it will go off shortly. The reason I check it is because some shady ass people will disable the light so you won't know there is a problem with the engine.

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#11 (permalink) Old 05-08-2004, 06:53 PM
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Quote:
Originally posted by TeeUp@May 8 2004, 05:28 PM
no, none of those smell....
Probably not the cat then, you can breathe a little easier(ha ha me so funny=double meaning).

The O2 sensor sounds logical, if you
1. Haven't run over anything (or anyone)
2. Haven't noticed any engine troubles

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#12 (permalink) Old 05-08-2004, 07:17 PM
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the car runs smooth... its just the thougth that something is not right here....
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#13 (permalink) Old 05-08-2004, 07:20 PM
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Sorry, didn't mean that you don't have to do anything, I just meant it is probably no big fix.

Yes, if my obc told me to do something i would do it immediately if not sooner.

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#14 (permalink) Old 05-08-2004, 07:29 PM
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oh no, you did not mislead me to think otherwise.....

in fact i have ordered the O2 sensors and will get them installed as soon as i possibly can....

was just kinda weary that it could be my cat that has gone wrong. well, i hope not.
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#15 (permalink) Old 05-08-2004, 09:51 PM
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I have a stupid question TeeUp, did the check engine light come on while you were in top gear maybe going 45-60moh?

Its gonna sound queer, but I get the same obd code (except I get 2 codes, one for each bank of cylinders) when I drive either into a strong head wind, or at low speed in 5th gear.

I feel your pain, but if an O2 sensor was malfunctioning, wouldn't it throw a code for it?

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