I replaced the cat about a month ago, and I recall only one O2 sensor. Is this correct, or is my memory faulty? If there is only one, how is the cat's functioning monitored? On my Miatas, and I suppose a lot of other cars, there is a sensor at the exit of the cat, that checks to see if the cat has done it's job. If that isn't there, what does the RX use?

 

2
one is pre cat and one is behind the cat. the one in front of the cat is expensive, behind not so much.

beers

 

Thanks.

 

To add:

The front one is an AFR sensor aka wideband sensor. Instead of voltage swings, it gives a lambda value to the ECU so it can adjust the fuel trims.

The rear one is a more traditional O2 sensor aka narrowband. It does the normal voltage swing and all it really does is checking if the cat is working.