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Discussion Starter · #1 ·
Hey all, I have a 2007 chevy equinox with the 3.4l v6. Recently, since I performed a tune up I noticed I'm getting bad milage, and the ecm is throwing a p0171 code (lean bank 1). The vehicle runs and idles smoothly and I'm not having any drivability issues, other than it's only getting 10mpg around town, and maybe 20mpg on the freeway.

I possess a bi directional scantool so decided to look at the data stream, I noted that the O2 1 voltage reading stays at 0mv no matter what the RPM of the engine, or speed the vehicle is driven at. The O2 2 voltage seems to sit steady around 800-900mv without any fluctuations. As I said, the vehicle is running rich, and I've read that such conditions can cause the first o2 sensor voltage to remain at or near zero.

I've done all the following things to attempt to remedy the situation, with no success.

Changed the air filter, inspected all vacuum lines for breaks or leaks, removed and cleaned the MAF sensor. I also purchased a can of B12 chemtool and added to the tank today.

I have purchased a top end gasket kit and planned to remove/replace the upper and lower intake manifolds and replace their gaskets/bolts, but I started to think.

Could the O2 sensor just be bad?

I reset the fuel trim and cleared the DTCs then observed the data stream, the readout from the 1st O2 sensor fluctuated slightly between 0 and 3mv for a couple of minutes before returning to a zero value - the second sensor remained fairly steady, fluctuating between 600-900mv for a couple of minutes until the ecm adjusted the fuel trim back to a rich condition.

Any thoughts, suggestions before I jump in to replacing the manifold gaskets?

Thank you in advance
 

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Any fluctuation of fuel reading will throw off upper O2 sensors, which then will throw off all fuel/air adjustments. I would say, replace the O2 sensors and spark plugs, prior to replacing manifold gaskets
 

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Discussion Starter · #4 ·
Any fluctuation of fuel reading will throw off upper O2 sensors, which then will throw off all fuel/air adjustments. I would say, replace the O2 sensors and spark plugs, prior to replacing manifold gaskets
I have replaced the spark plugs and wires within the last 500 miles, I inspected all the vacuum lines I could find and they are all in good condition, I inspected the hard plastic vacuum lines for breaks and even removed them and checked that air could pass freely through them. I also replaced the orings on the pcv to intake manifold tube (as it was a bit loose on the manifold side).

I think I will maybe try to replace the upstream O2 sensor before ripping into the intake manifold.

Thanks for the input.
 

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Sensor position 1 on both banks should be fluctuating from -3 to + 3 normally with a good O2 sensor when reading the short-term fuel trims if there are no other issues like vacuum leaks.
Position 1 controls fuel, position 2 O2 sensor just monitors the cat functions and it's reading will stay ''flat''.
 

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2008 Equinox LS AWD Summit white, 2007 Torrent GT FWD Jet Black, 05 Pursuit 2.2L Titanium Metallic
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Check the line going from the intake tube to the rear valve cover. These tend to get knocked out during spark plug and services in the back of the engine bay. Ive done it inadvertently countless times.
 
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