Hi,
I've had my CEL on for a while now, but I haven't really had problems with fuel economy until a few days ago. I checked the error codes and I got P0171 (System Too Lean Bank 1), and P0134 (O2 Sensor Circuit No activity Detected Bank 1 Sensor 1).
Usually, I get about 200kms on half a tank, but this last week has been way below that. I got about 100kms on half a tank.

I searched online and saw that some people that had those error codes have replaced the Upstream O2 sensor and that fixed the error codes.

The car does have a CAI installed.

Can anyone else help me out if they know what sensor it may me or somewhere I can find more details to pinpoint the problem?
I used BlueDriver app to get and read the error codes.

Thanks!

 

 

Replaced the upstream O2 sensor, and the CEL went away, but I'm still having poor fuel economy. It wasn't as bad as when the O2 sensor was dead, but it's what I've usually had before. Any ideas on this?

 

Even if the lean code is gone, you may still have a vacuum leak somewhere, especially if someones been messing about in the engine bay. Look up vacuum leak smoke out test. It's an easy way to find leaks, all it takes is a cigar or vape.

On an unrelated note, check to see if the splash guards behind the bumper are missing. I lost 5 MPG when I took mine out.