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Old 02-12-2011, 12:55 PM
CF Junior Member
Join Date: Feb 2011
Location: Salem,NH
Posts: 32
Default O2 sensor causing bank 1 too lean?

I have a 2004 GMC SIERRA 5.3L vortec. Plugged in my Actron 9185 scanner, code is P0171 Bank 1 too lean. So I viewed engine datastream and found O2S11 v is a steady 0.000. I assume I have a bad drivers side Pre-catalytic converter O2 sensor? I also get an occasional random\multiple cylinder misfire. but I believe O2 sensor is causing this as well, Just wondering if I am right or should I troubleshoot elsewhere.
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Old 02-13-2011, 03:53 AM
CF Veteran
Join Date: Nov 2009
Location: sacramento,ca
Posts: 1,041

if the scanner is saying 02 sensor bank 1. i would start with replacing that specific sensor.
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Old 02-13-2011, 07:30 AM
CF Junior Member
Join Date: Feb 2011
Location: Salem,NH
Posts: 32

I did replace that O2 sensor, idle made considerable improvement. after 15 mins of idle engine light returned code isbank 1 lean intermittent, Im thinking that the pcm has to "recalibrate" for the new sensor?
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Old 02-17-2011, 09:07 AM
CF Beginner
Join Date: Feb 2011
Posts: 2
Default codes

if your pcm does not "re-calibrate" you might want to check your intake manifold gasket. It will cause a lean condition on bank 1 and bank 2 and have low/rough idle.
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Old 02-17-2011, 08:12 PM
CF Beginner
Join Date: Jan 2011
Location: Amarillo, TX
Posts: 21

It's not the o2 sensor. Granted, the sensor may have been going bad, but the bank 1 (or 2) lean codes are not caused by o2 sensors. The o2 sensor is telling the PCM that the fuel ratio is to lean. If it was somehow causing that issue, the PCM would be able to adjust it out. The ratio is to lean because either the MAF is reading incorrectly, or unmetered air is getting into the combustion chambers. So either your MAF is reading incorrectly OR you have a leak in the intake stream after the MAF.
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Old 02-17-2011, 08:12 PM

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