Hi everyone. New here. My winter vehicle is a 2000 olds bravada. 150 k miles, runs great, new fuel pump, new transmission.

Im getting a check engine light for "running too lean"...this happened a couple weeks after the fuel pump replacement. my thought is a bad o2 sensor, although no idea which one. after looking at them, the o2 sensors appear fairly new. still runs great. any thoughts??

 

Try the fuel filter and see what happens.

 

If the fuel filter doesn't fix it, I think it is probably the O2 sensor. I'm not certain how they are set up on the Bravada, but on other GM vehicles, the sensor downstream of the cat is only used for checking cat function, not altering fuel mixture. You might try switching them to see if you can isolate the bad one.