So these cars of ours have FOUR O2 sensors whose recommended change interval is 100K miles. Well, what's the harm of changing just the pre-cat sensors (aside from a false code due to greater delta readings from pre to post-cat sensors indicating bad cats)?

 

i think only the pre-cat o2 sensors have a 100k miles interval. and if i'm not wrong there are 3 in a v6 and only 2 in a i6. they are not cheap so i wouldn';t change them unless they are causing problems like an error code or bad gas mileage. if it isn't broke, don't fix it.

 

Bad gas mileage...

I can also smell a richer exhaust condition... black soot residue on the pipe is also a sign.

 

Maf sensor can cause that too

 

Oh, I've done the MAF already (last month, for CEL 0170 and 0173). Matter of fact, I think my original MAF is still good.

 

at 100k they are lazy.Renew the 2 precats if on a budget since they are the ones that oscillate the a/f ratio.The post cats are along for the ride and monitor cat function at a base line.Best performance and mpg will always be achieved with all 4 renewed.You can pick up the universal splice in ones with the new connection system for about half the cost.

ohlord