This question is probably for toyomoho or another tech but I'll take input from anyone.

toyomoho posted on another thread that the A/F sensor tends to get lazy with use and suggested it be changed when the poster complained about poor gas mileage.

My5FSE has 2 oxy sensors. One is the main (single wire) andthe otherafter
the CAT is the Sub Oxy Sensor (2 wire). I don't consider either of these to be an
A/F sensor as I think that would require a sensor with a wider range and maybemore signal wires.

I assume the main is non heated and the sub is heated (second wire). I bought this car used with no known service history andnow with close to 149K so is it advisable to replace either or both of these sensors as a normal maintenence procedure?

There are no drivability issues and an inspection of the plugs a short time ago showed no rich burn condition. I never have calculated the gas mileage because I usually never fill to top on any one gas up.

Advancesells the main (single wire) generic Bosch with no wire connector for about $35 and with connector for about $110. Dealer wants about $140 for the main and over $200 for the sub.

 

i will suggest 120k for my customers ,but if you're a tech. should be be able to test how activethe o2 sensor is and determind if you want to replace it.

 

The test seems to be just a voltage reading, but will that show the reaction speed, or does that matter?