Where is the rear 02 sensor on your 99 miata?
In 1999-2000, Mazda designed 2 exhaust versions.
The most common version is the Federal-spec Miata. This exhaust system has the typical, single catalytic converter with an O2 sensor before and after it.
- The front O2 sensor is before the catalytic convertor and can be seen by removing the driver's side wheel.
- The rear O2 sensor will be just after the catalytic converter, at the 12 o'clock position between the rear wheels.
The California-spec Miata had a precatalytic converter directly installed on the exhaust manifold/header, as well as the standard catalytic converter running the length of the engine.
- You will find the first O2 sensor directly on the header, just above the pre-cat. It is easily seen from the driver's side of the engine bay.
- The second O2 sensor is found just below the pre-cat, but before the main catalytic converter. It is easily seen by removing the driver's side wheel.