I just bought a new O2 sensor, NTK brand. The installation instructions have different torque specs for either the M18, or M12 sensors. My question is how do I tell which I have? I haven't the slightest clue.

Additionally, NAPA wanted like $180-$200 for the rear O2 sensor - is this outrageous or is it normal? Furthermore where is the rear O2 sensor? I quicly followed the exhaust the other day and didnt see another one. If you had to align it with the car, roughly where would it be? Rear wheels? Rear seat? Fuel filter? Like around which level?

Thanks

1997 Pontiac Sunfire
2.2 L OHV
Manual

M18 is the most common on cars today. Look at the threaded area. Does it look like 12 or 18mm diameter?

Ya I think M18 is right, I just busted out my ruler and it seems to be 17-18mm or so. Plus I need a 22mm wrench to work on the thing, so 18mm thread seems reasonable - 12mm would be almost 1/2 the size of the hex portion.

The rear O2 should be right after the cat.



Tinkles

2003 Cavalier 1SV
Bagged and Blown

and is $180 reasonable for the rear O2 sensor? Why is it so much more expensive? Can any other O2 sensor be used?