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PO420 / B1 code

 
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John Vollenweider



Joined: 02 Mar 2006
Posts: 52
PostPosted: Mon Jun 16, 2008 11:18 am    Post subject: PO420 / B1 code Reply with quote
I cleared PO420 code , What O2 sensor / or sensors should I replace if any.
Any help would be appreciated.
I have 97 528i.
Thanks John
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edjack



Joined: 04 Feb 2002
Posts: 3887
Location: San Jose, CA
PostPosted: Mon Jun 16, 2008 6:18 pm    Post subject: Reply with quote
This code denotes "Catalyst Efficiency Below Threshold, Bank 1". Either the cyl 1-3 post-cat O2 sensor is bad, or the cat is bad.

Cheaper to replace the sensor to see if the problem goes away.

You should get the Bentley's service manual.

You should mention the mileage in your post: cats are normally replaced at 100k intervals.
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Ed BMW CCA member since 1987 (Nr. 62319).
'97 540i 6 speed Aspensilber over Aubergine interior.
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