My buddy's Lexus (RX?, the Rav4 clone) has a P1155 code I diagnosed for him. After clearing it came back the very next day, making me think it's something imminently wrong as if it was a random code, then it would take some time to come back.
First thought was just replace the air/fuel sensor, but then I thought of the things that lead to that sensor...
air filter, MAF sensor, throttle position sensor, fuel injectors.

What's the likelihood those things are needing to be fixed verses the sensor itself? Those sensors are supposed to last a while aren't they? His is a 03, no idea if it's the original sensor, he's only owned it for 4 years.