O2 replacement questions

[Andrew Larson]

I have a 98 4runner with 143k on it. I figure O2 sensor replacement would be some good maintenance since it is scheduled at every 75k. I have done alot of reading on this and still have some questions. Is it best to replace both, it seems as though quite a few have said to replace just the one past the catalytic converter (which is the rear/downstream i assume)?

 

[TheDurk]

I have a 98 4runner with 143k on it. I figure O2 sensor replacement would be some good maintenance since it is scheduled at every 75k. I have done alot of reading on this and still have some questions. Is it best to replace both, it seems as though quite a few have said to replace just the one past the catalytic converter (which is the rear/downstream i assume)?

It depends. If both are original, and there are no codes, the front one is more important. The front sensor affects performance, the rear one just sets codes. But in your case, I'd do both.

 

[nissanh]

Do the front sensor. Rear sensor checks the performance of the catalytic converter. Since you are not in CA, you don't have to worry about the rear.

Buy DENSO and nothing else. I bought mine for $45 on ebay.

 

[RS Dude]

Wait until you get the check eng light, then replace both.