Replaced 02 sensor, now code P0171 is showing

gearyr

Test Drive
2010 Xterra 156,550 miles on it. I had to replace the Bank 1 Sensor 1 02 sensor. The cel is still after put in the new 02 sensor. So I ran a scan it showed P0171. I haven't drove but around 15 miles to see if the gas mileage went up. It was 8 mpg, now 21 mpg with the new sensor. I don't know what the P0171 is for and how to get the cel off
 

gearyr

Test Drive
Yes I did. Drove for a while cel stayed off. cel came back on this morning after driving abot 20 miles. I'm stumped. Guess I'll have to take my vehicle to a mechanic
 

TerryD

Total Tease
Supporting Member
Location
Covington, Va
The code is a bank 1 lean. That could be a cracked manifold, or a leaking manifold flange or even an injector stopping up.

I would start with pulling the spark plugs on both banks and seeing if the passenger side plugs are a bright white, indicating lean on that side (bank 1). If they are really dark brown, then your leak is most likely after the combustion chamber and causing the ECM to over fuel that bank.
 

gearyr

Test Drive
I did a hard reset on the ecu. CEL is off and has stayed off since Saturday. I ran the scan tool again tonight. Now it's showing P0420. But the cel is off. I have to have my vehicle go through the emissions test by the end of November. So I am stumped on what to do
 

XterraRising

Need Bigger Tires
Supporting Member
Location
Utah
P0420 is for Catalyst System Efficiency Below Threshold (Bank 1). if you used a cheap O2 sensor, it could throw this code, but it often means your catalytic converter is junk. But you’d also want to check your exhaust manifold for cracks. If you were running lean, then you were running hot. That can mess up a lot of things in the exhaust system.
 
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