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AZBMW Forums › Model Specific Discussion › 5-8 Series › e39 p0420 CEL code
e39 p0420 CEL code
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xekret_e36
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PostPosted: Fri Sep 02, 2011 5:50 pm
Post subject: e39 p0420 CEL code

I decided to buy a 540i and after having it for a day it threw a code. I took it to autozone and they told me it was the p0420 which could be a bad cat or one of the oxygen sensors. I accidentally put 87 octane gas twice not thinking about it and was wondering if that had anything to do with it? Does anyone here have any experience with that code? Also the PO said the original owner replaced the cats with high flow cats about 5-10k ago. Any comments are appreciated.
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Evilsmith
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PostPosted: Fri Sep 02, 2011 7:48 pm
Post subject: Re: e39 p0420 CEL code

More likely that its the O2 sensors in my experience, if youre going to start swapping parts, start there first.

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crazycast2
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PostPosted: Fri Sep 02, 2011 7:59 pm
Post subject: Re: e39 p0420 CEL code

Why did the original owner put high flow cats on it? It could not be running right and that's what caused the original cats to go bad and instead of fixing the problem he just put new cats on as a temporary fix. Aftermarket high flows are way cheaper than OEM.

How's your gas mileage?
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xekret_e36
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PostPosted: Fri Sep 02, 2011 8:30 pm
Post subject: Re: e39 p0420 CEL code

crazycast2 wrote:
Why did the original owner put high flow cats on it? It could not be running right and that's what caused the original cats to go bad and instead of fixing the problem he just put new cats on as a temporary fix. Aftermarket high flows are way cheaper than OEM.

How's your gas mileage?
I have no idea why the original owner replaced the OE cats. I asked the second owner and he did not know as well. He did tell me the original owner was super anal about maintenance and kept a record of his gas mileage in a little notebook. My gas mileage is about 18-20 city. It says 19.2 on the OBC.
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crazycast2
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PostPosted: Fri Sep 02, 2011 9:14 pm
Post subject: Re: e39 p0420 CEL code

xekret_e36 wrote:
crazycast2 wrote:
Why did the original owner put high flow cats on it? It could not be running right and that's what caused the original cats to go bad and instead of fixing the problem he just put new cats on as a temporary fix. Aftermarket high flows are way cheaper than OEM.

How's your gas mileage?
I have no idea why the original owner replaced the OE cats. I asked the second owner and he did not know as well. He did tell me the original owner was super anal about maintenance and kept a record of his gas mileage in a little notebook. My gas mileage is about 18-20 city. It says 19.2 on the OBC.

Sounds like a rear O2 sensor then.
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xekret_e36
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PostPosted: Sun Sep 04, 2011 3:16 pm
Post subject: Re: e39 p0420 CEL code

Ill start with that. Thanx.
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xekret_e36
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PostPosted: Wed Oct 26, 2011 12:18 pm
Post subject: Re: e39 p0420 CEL code

Update, replaced the post cat o2 sensor and the CEL light went away for a few days but came back on last night after a long drive. There is like a rasp noise when i rev it so I'm guessing that is not a good sign.
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killerkiko
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PostPosted: Wed Oct 26, 2011 12:22 pm
Post subject: Re: e39 p0420 CEL code

Get the codes read, it may be something different. Its possible that the cats were replaced with shitty ones causing the honeycomb matrix inside to break early. If this happens, the exhaust does not get "filtered" as well and can cause your car to not run correctly and throw a code.

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Evilsmith
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PostPosted: Wed Oct 26, 2011 12:26 pm
Post subject: Re: e39 p0420 CEL code

Also, if you rolled around with bad O2 sensors long enough it will screw up your cats eventually

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killerkiko
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PostPosted: Wed Oct 26, 2011 12:30 pm
Post subject: Re: e39 p0420 CEL code

Evilsmith wrote:
Also, if you rolled around with bad O2 sensors long enough it will screw up your cats eventually

yep, and once the cat goes, it will then foul the new o2 sensors you just put in.... so get those codes read asap

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xekret_e36
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PostPosted: Wed Oct 26, 2011 1:17 pm
Post subject: Re: e39 p0420 CEL code

I got the code read last night as soon as i saw it and it was the same p0420 i had before i replaced the o2 sensor.
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ccc13
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PostPosted: Wed Oct 26, 2011 1:54 pm
Post subject: Re: e39 p0420 CEL code

And so it begins... Do you know if either PO replaced the valve cover gaskets and CCV? That's usually the cause of cats going bad on the M62: CCV fails, oil leaks in places it shouldn't (i.e. intake manifold and check your spark plug wells), gaskets go bad over time (check for oil leaking out between the head and valve cover), and all that unburned garbage has to be burned somewhere.

Mine started with a cat efficiency code, then misfire codes (mostly concentrated on bank 2), then noticeable misfires and power loss. O2 sensors were replaced, plugs were replaced, nothing. Then I remembered the CCV and gaskets; replaced them and the cats, and bingo! Car was back to being a champ.

I'm not saying that's definitely your problem, but it's a likely candidate. I'd do all the cheap stuff first though: O2s and plugs.
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ccc13
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PostPosted: Wed Oct 26, 2011 1:57 pm
Post subject: Re: e39 p0420 CEL code

On second thought: since they are high flow cats, you might get an intermittent efficiency code simply because they simply don't clean up as well as the ECU thinks they should. Any idea on the make/model of your cats?
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KINGAMR
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PostPosted: Wed Oct 26, 2011 2:44 pm
Post subject: Re: e39 p0420 CEL code

ccc13 wrote:
And so it begins... Do you know if either PO replaced the valve cover gaskets and CCV? That's usually the cause of cats going bad on the M62: CCV fails, oil leaks in places it shouldn't (i.e. intake manifold and check your spark plug wells), gaskets go bad over time (check for oil leaking out between the head and valve cover), and all that unburned garbage has to be burned somewhere.

Mine started with a cat efficiency code, then misfire codes (mostly concentrated on bank 2), then noticeable misfires and power loss. O2 sensors were replaced, plugs were replaced, nothing. Then I remembered the CCV and gaskets; replaced them and the cats, and bingo! Car was back to being a champ.

I'm not saying that's definitely your problem, but it's a likely candidate. I'd do all the cheap stuff first though: O2s and plugs.
This. Owning a 540i sucks. I would get rid of it if you don't like doing maintenance at shitty times.

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xekret_e36
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PostPosted: Wed Oct 26, 2011 5:08 pm
Post subject: Re: e39 p0420 CEL code

ccc13 wrote:
On second thought: since they are high flow cats, you might get an intermittent efficiency code simply because they simply don't clean up as well as the ECU thinks they should. Any idea on the make/model of your cats?
Thanx for the suggestions. The guy I bought it from had no idea the make and model of the cats, all he knew was that they were replaced about 5 to 10k before i bought it. I doubt they were shitty cats because the PO before him was super anal about maintenance. Although the left valve cover gasket, engine mounts and other miscelaneous stuff need to be replaced. Ill start with the plugs and gasket. Ill research about the CCV.
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