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2006 Chevy Uplander 2.5 will not smog due to P0171 code.

Customer Question
upstream O2 sensor switching as...
2006 Chevy Uplander 2.5 will not smog due to P0171 code. upstream O2 sensor switching as it should, but Downstream is on the rich side until RPM's pick up. Fuel trims range over 20 LT and 3 to 5 ST. As RPM picks up LT goes to about*****about 2. I have replaced the MAF and checked MAP etc with my scan tool. Checked for vacuum leaks with spray and propane.
Here is one clue. If I disconnect the MAF, it will run 0 ST and only 3 LT All fuel trims are Positive.
Submitted: 11 months ago.Category: Chevy
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Answered in 4 days by:
8/7/2017
Chevy Mechanic: Shawn Few ,
 replied 11 months ago
Shawn Few
Category: Chevy
Satisfied Customers: 144
Experience: Lead Tech at F1 Auto Service
Verified

Hey ,how are you
I seen That your post been sitting for a long time without an answer ,I 'm sorry for your long wait without getting an answer till now
I will try to help you on this issue if you have not gotten it resolved yet
Please Let Me Know
Thank You
ASE Certified Technician

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Customer reply replied 11 months ago
Still not resolved
Chevy Mechanic: Shawn Few ,
 replied 11 months ago

if you test drive it pull maf readings ,what is the readings when it changes gear from 2nd to 3r , what is the highest reading on the scan tool ,hopefully u have a good one with quick processor in it for a good refresh rate so u can see it

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