My check engine light came on on my 2005 Chevrolet Monte Carlo LS & the code was p0171. I took it to a mechanic & was told that I need to replace my upstream O2 Sensor. Once replaced, the code was reset but, not even a mile down the road, the light came back on. I took it elsewhere & was told that, had it been my O2 Sensor, the code would've specified O2 sensor but it was just reading bank 1 too lean which means that possibly a cracked or leaking hose somewhere around the intake. I'm not sure what to do...Help!

 

It's possible you have an intake leak (vacuum leak), but I would check the MAF sensor first. If it is dirty or malfunctioning it will set the P0171 code. So will a bad fuel injector, faulty PCV system or a problem with fuel distribution. The MAF would be the first thing I'd check though.

 

Also If its burning antifreeze.. (contaminated the o2 sensor)