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Malfunction code P0420 ?

 
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RickNeilH



Joined: 08 Jun 2007
Posts: 25

PostPosted: Sun Dec 07, 2008 4:31 pm    Post subject: Malfunction code P0420 ? Reply with quote

I had this code back in the summertime and although it was somewhat vague, I interpreted it as the right side cat failure.
The code reads: "Catalyst System Efficiency Below Threshold (Bank 1)".
I am pretty sure "bank 1 is the right (passenger) side.
I replaced the right cat with a BavAuto aftermarket one. Their P/N BMW1450-0, as well as new O2 sensors.
I had another P0420 fault code appear in early December so I believed the replaced cat was bad. I called in the warantee and replaced it again.
2 days later I have another P0420 fault code.
I am now trying to decide what this code really means or is the aftermarket cat just a pc of junk.

Any ideas?

Rick H
Northboro, MA
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1995 525i
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edjack



Joined: 04 Feb 2002
Posts: 3887
Location: San Jose, CA

PostPosted: Sun Dec 07, 2008 8:55 pm    Post subject: Reply with quote

Sounds like your post-cat sensor is bad.

Many of us who have OBD-II V8s, when we get this code, will replace the sensor before we replace the cat. Give that a try.

Bear in mind that many aftermarket cats are not worth buying. In fact, in CA, NO aftemarket cats are certified.
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'97 540i 6 speed Aspensilber over Aubergine interior.
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RickNeilH



Joined: 08 Jun 2007
Posts: 25

PostPosted: Tue Dec 23, 2008 1:59 pm    Post subject: Reply with quote

I haven't gotten around to replacing the post cat sensor yet. I replaced both sensors with new when I changed the cat but I suppose one could be bad out of the box.
One thing I have noticed, however is, when the undercarriage gets good and wet, like in a heavy rain, the check eng light goes out for 4-6 days.
Then it comes on again. This has happend twice.
I suspect a bad connection and will take a look.

Rick
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edjack



Joined: 04 Feb 2002
Posts: 3887
Location: San Jose, CA

PostPosted: Tue Dec 23, 2008 3:21 pm    Post subject: Reply with quote

Are you saying you replaced the post-cat sensors? If so, were these aftermarket, or OEM?
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'97 540i 6 speed Aspensilber over Aubergine interior.
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RickNeilH



Joined: 08 Jun 2007
Posts: 25

PostPosted: Tue Dec 23, 2008 4:09 pm    Post subject: Reply with quote

Both Bosch, pre cat 13559, post cat 13475, from AutoZone however.
That may be the issue, but new Bosch parts?
Unusual and I don't believe an O2 sensor is that complicated that it could be bad out of the box.

Rick
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