Why would two O2 sensors would fail at 38k miles on my best friend's 2000 C4 ?

Paul

 

Does he run premium gas all the time from a brand gas station? Also any mods on his car? If he gets a check engine light, I'd reset it first and see if the CEL comes back before changing the sensor(s). He may also try cleaning the contacts first. There are a few 02 sensors (4 IIRC).

 

Thanks for thoughts and ideas . . .I'll pass this thread on to him and let him respond.

Paul

 

What's makes him think that they both failed? Extremely unlikely. Someone probably just read the fault codes which stated that the sensors were out of range. 99.9% of the time, this is an indication of a fuel/air mixture problem unrelated to the O2 sensors. The sensors are just telling you there is a problem upstream.