I have a 99 4runner Limited .How many 02 sensors it has? and where are they located? I'm doing a tune up and want to replace them,it has 72,000 miles.no check engine light or any problems,just want to replace them before they fail

 

Climb underneath and look at your exhaust. Look for wires connecting to your exhaust. These will be the O2 Sensor or sensors.

 

I think 49 state emissions 1999 model has an air/fuel sensor in front of the cat and an O2 after.

 

Ok thanks

 

If you have no codes, the only one worth replacing is the sensor in front of the cat.

This should help if you want to do the job yourself:
http://www.ultimateyota.com/index.ph...26&topic=305.0

 

72k on an o2 sensor is nothing since you'd probably get another 70k out of it or at least wait til 100k.

 

ok thanks I guess I'm going to wait longer,I just tough it should be replaced at 80k so I was going to do it now but I'll wait