Overlordexo

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

ruley73

Yes, based on the info you provided I think the upstream oxygen sensor (what you referred to as "O2 1") is definitely bad assuming there aren't any wiring issues. I highly recommend replacing it with an OEM/AC Delco, Denso or NTK sensor (Denso is actually the OEM supplier). Do NOT use a Bosch sensor sold at the big box parts stores. They're garbage.

Overlordexo

Haha, well an update here. It was indeed the O2 sensor that was causing the issues. Got it swapped out and drove the car around for a bit - fuel trim is looking much more manageable and the mpg jumped back up into the 15/mile range. (Just driving in city, have not taken it on the highway yet)

Sadly, wish I would have read this before I purchased the replacement. Was a bit short on money so ended up buying the Bosch one. So I'm guessing I'm going to end up replacing it again sooner rather than later.

So the next one I buy will be Ac Delco or denso.

Thanks for the help guys!