Engine trouble code 171

[wgb]

I have a 2wd '95 Ranger with the 4L v6 and 5 speed trans. It starts and runs fine, but it has a 171 engine code (lean on bank 1). What are some common causes for this code? I am a shade tree mechanic and can usually fix problems with my cars. But I need some help knowing where to look for this problem. No drivability problems, just don't want to burn a hole in a piston and have a real problem. All suggestions will be appreciated and followed up.

 

[SenorNoob]

Has that O2 ever been replaced that you know of? They do have a lifespan. I think as they wear the they read leaner. What do the plugs look like on that side? It does have 2 O2 sensors right?

I'd expect a anything else (except a single clogged injector) to set a code for each side. Low fuel pressure or vacuum leak, etc.