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Working on my son's 2012 LS 1.8 84,000 miles on it. Changed out the oil cooler, and T-stat housing assembly with new parts, and everything looks dry now, but once it was all back together it threw a Bank One Lean code. It seems to run fine, and no codes before the parts were replaced. Idles perfect so I'm ruling out an air leak. Just checked fuel pressure, and it settles in at 60 with the engine at 3000 rpm, so I've ruled out low fuel pressure. I did spray water around the motor compartment at the car wash after it was all back together. I'm thinking upstream O2 sensor? I just un plugged it, and used compressed air to blow out the electrical connector, disconnected the battery for an hour or so, and took it for a 20 mile drive. Runs good, and no code........... yet.
Any thoughts would be appreciated.
 

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Resetting the ecu may have done it if you did not do so when replacing the t-stat. Seems like these cars do weird things when stuff is unplugged and the ecu still has power. Orrrr... possible that a vacuum line was loosened. Lots of things could be.
Could have been a corroded connector. Really need to see if it comes back...

I suggest either a bluetooth obd2 scanner or I love the ultra gauge for the money, I have had my v1.2 for 8 years and it has helped me diagnose and repair 4 vehicles, as well as reset codes for friends. thing I like about the ultragauge it shows pending trouble codes. I was getting a pending p0301 in my ranger every 3days about the same distance from home. Turned out to be a sparkplug wire was starting to swell and need replaced.
 

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Working on my son's 2012 LS 1.8 84,000 miles on it. Changed out the oil cooler, and T-stat housing assembly with new parts, and everything looks dry now, but once it was all back together it threw a Bank One Lean code. It seems to run fine, and no codes before the parts were replaced. Idles perfect so I'm ruling out an air leak. Just checked fuel pressure, and it settles in at 60 with the engine at 3000 rpm, so I've ruled out low fuel pressure. I did spray water around the motor compartment at the car wash after it was all back together. I'm thinking upstream O2 sensor? I just un plugged it, and used compressed air to blow out the electrical connector, disconnected the battery for an hour or so, and took it for a 20 mile drive. Runs good, and no code........... yet.
Any thoughts would be appreciated.
Welcome Aboard!(y)

There are many things that can cause the P0171 trouble code on the Chevy Cruze. Here are the most common ones.

  • Vacuum Leaks– With the Chevy Cruze, one of the most common cause for the P0171 code to show is a vacuum leak. Take a look around and see if you can find the vacuum leak. Here’s a great YouTube video on how to find a vacuum leak.
  • Oxygen Sensor– The P0171 codes is thrown when the oxygen sensor(s) do not register enough oxygen in the exhaust. When the oxygen sensor is bad, it can cause a false reading and trigger the code. The computer will still adjust the air/fuel mixture to compensate. This will cause the Cruze to run rich. O2 sensors are relatively affordable.
  • Mass Air Flow Sensor– The mass air flow sensor calculates the volume of air entering the engine. If it has gone bad, the air fuel mixture will be off and the P0171 code will show.
  • Bad Fuel Injectors– If you have one or more fuel injectors that have gone bad that can certainly cause the air/fuel mixture to go bad.
  • Fuel Pump/Fuel Filter– Today’s modern fuel injected motors need a lot of fuel pressure to atomize the gas properly. If the fuel pressure is not as high as it needs to be this atomization doesn’t happen properly and the optimal air/fuel mixture isn’t achieved.
  • Air Filter– While it’s not the most common reason to throw the P0171 code, a clogged air filter certainly can cause the code to throw. And, since it’s so easy to check, why not look?
Just in case, read this:
2011-2016 Cruze 1.4 PCV Valve Cover/Intake Manifold Issues

Don't forget to introduce yourself and your Cruze
here.
 
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