I have a 2005 Mazda 6s. It has four O2s. One in each exhaust manifold and one just below each catalytic converter connected to each exhaust manifold. Simply said 2 behind the radiator and 2 in front of the firewall. Have fun. If you didn't know, the 2005 Mazda 6s (V6) has four catalytic converters. One on each exhaust manifold and two more before the muffler. Go figure!
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If it's a V-6 engine it will have 2.
( 2 sensors ) - # 6 fuse - 15 amp - HEGO sensors ( in the fuse panel in the drivers end of the dash )
If you have a 4 cylinder engine, you will have two. On a 6 cylinder, you will have four.
Assuming you have the V-6 engine, it has two downstream (after the cats) O2 sensors and two upstream (before the cats) Air/Fuel Ratio Sensors. So the answer to your question is two O2 sensors.
A Mazda 6 s requires 6 plugs, A Mazda 6 i requires 4
Mine is an automatic and it has 3. one on each exhaust manifold and one after the cat.
Your engine will have 4 O2 sensors. And all of them will have a different part #, because the connectors are all different.
That all depends on the engine size. 4 or 6 cyl? Do a Google search on your model and engine and there are many places that will show you. Once you do find it, you will need special tools. You may want to pay the local shop to do it for you. It will take them only a matter on minutes to replace it....