Originally Posted by Jon316G

I would stick with the OEM sensor.

Originally Posted by Taz Ismail

Thank you very much for the quick reply. Can you tell me where the Sensors are located?

Originally Posted by Huey52

Note parts '6' and '9' in the enclosed for O2 sensor locations (one on the exhaust manifold and one on the Cat).

Originally Posted by Vyndictive

You can replace the sensor yourself, however, this is not what I would call "easy" as exhaust bolts are the worst in the world to remove.

There are two ways that I can think of to do this:

1st way (the way I've never done)
1. Disconnect o2 sensor wiring harness from above cat (this will be a very tight fit and i'm sure it can be done)
2. remove o2 sensor guard pictured in Huey's diagram. This has two bolts on each side the protect the sensor from stuff your run over.
3. Use a wrench and try to remove the sensor itself.

Again, all these bolts are going to be heat cycled on there and rusty because mazda has never heard of stainless steel fasteners. In theory, its real easy, but in practice, I'm not so sure.

The other way is to remove the cat, and with the car off the car, remove the sensor.
Remove the cat by disconnecting the front flange from the header (3 bolts, all of which will require a breaker bar or impact wrench when it will fit) and the rear flange (2 spring loaded bolts with donut gasket)
And disconnect the o2 sensor wiring harness from the body.

Exhaust bolts are a huge paid in the ***, so good luck. (JonG and I know about this first hand....)

If you're going to go through all the trouble, might as well get a mid pipe and at least gain some HP in the process.

Originally Posted by Gish

What is the part number for the rear O2 sensor?

Originally Posted by CRX Millennium

n3h3-18-861b