Here are the codes from my Elm-II and I have scanned it with a Bosch at the local parts store and used a friend's konwie. All the codes.
I have a 2002 Monte Carlo 3.4L and Now I'm curious about which one is the most likely cause of it running to Lean(P0171). I know I have a exust leak, So that's one issue resolved when I can replace the whole thing but I'm pretty sure this is not the main issue. Replaced 02 sensors last year with Bosch upstream and downstream sensors, Now I wish I went with A/c Delco since it's a GM.

I had the catlylic converter replaced last year with a magnaflow also since the honey comb was plugged up.

Any help would do for help on any code & Thank You.

 

A faulting O2 sensor can make the car run lean.

 

Where's the exhaust leak? If it's before the sensor, you could be getting inaccurate readings and the car leaning out when it shouldn't.