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Hi to all, Can anyone tell me how many oxygen sensors does a 2001 nb have. Had a fuel miser sensor fitted and now it runs with flat spots until it has completely come up to operating temp.
Thanks in advance

pretty sure its just the one. down near the bottom of the headers somewhere, but ill let someone else with more knowledge confirm.

Mazda's NB8B parts catalogue shows 2 sensors: 18-861B (No 1) and 18-861B (No 2)

99 has only one.

however, the NB uses a 4 wire sensor, 2 of the wires are for a heating element to preheat the sensor so it warms up earlier.

NA sensors are one wire, and use the exhaust gases to heat up.


If the heating wires aren't connected, or connected wrongly, the sensor may be giving the ECU wrong information until it's warmed up.

Thanks for the help, I cannot find one after the cat. The sensor fitted had the plug fitted and was to suit 2001, however I wonder if there is a difference between a pre cat. One and a post cat. One. As I don't know what one was fitted

Reading further on the parts book they were initially the same, then they changed the one after the cat from 861B to 861C. Really I'm just going from what Mazda list about it and memories from years ago that there were one pre-cat and one post-cat on NB8Bs.

Make sure the one you order is LONG enough, I had ordered one that very short, so I had to weld the new sensor with the old wire. I am quit sure that it is about a meter long.

The NB "post cat" sensor was for California emissions control-we don't have this so if you have a factory exhaust, it's probably just plugged.

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