Where is the O2 sensor located on a 2000 Mazda Millenia?

Answer 1

The Millenias and their Commonwealth cousins the "Xedos" all suffered a common defect resulting in MOST CEL issues. This engine configuration typically results in the need for replacement of 1 to 2 O2 sensors and / or the DREADED KNOCK Sensor embedded deep in the Manifold assembly. Mine ran 3 years with this CEL on due to the cost of labour one item to replace. The sensor was only 165 bucks while the labour to install was nearly 800.

I will admit once it was replaced I was not only legal again for the Emmissions test, but the thing ran smoother than it ever did ina ll seasons PLUS I got nearly 2 points to my highway Mileage.

Now the codes are confusing on this because two of the O2 sensors share the same circuit and the code wont necessarily identify WHICH o2 is actually bad, that unfortunately is hit or miss. The KNOCK sensor code is separate and distinct however but all will result in a costly set of repairs.

So to answer your question a different way, there are 4 O2 sensors all over the compartment PLUS the knock sensor in the Manifold.

Only One of the O2 sensors is even visible much less service-able by the average DIY person.

Good Luck, Been there (3 times now)Done that.

Pay somebody, you will live longer.