Mazda 3 Oxygen Sensor

Hi there,

I am the owner of a 2006 Mazda 3i touring, with around 94,000 miles on it. My engine light recently came on and I was told by the Mazda dealership (yes, I still take my car to the dealership for maintenance…although I am now rethinking this) that my oxygen sensor needs to be replaced and that it would cost me around $465, which includes labor, I believe.

I took it to another mechanic for a second opinion and now he is telling me that it is best to replace all of them when one goes out, since they run off of each other. He is quoting me $242.03 for just the one sensor, plus whatever his labor cost is, and is insisting that I have all three replaced (which would cost around $1,000).

I am at a loss. I don’t know who to believe. I know either way it is going to cost me, but I just don’t know which route to take. Any help would be greatly appreciated!


My daughter has an 05 mazda 3. I changed the post cat o2 sensor two years ago, and the others are still OK. The sensors operate independently, so you can replace just one.

They don’t “run off each other.” Just change one. And don’t go back to the mechanic who pressured you to change all three.

I’m wondering what checks were done to verify that you need an O2 sensor. The check engine light means that there were error codes. The error codes look like “P0123” and none of them can tell you that an oxygen sensor is bad. All codes still require diagnosis.

The code was PO030 I believe. The dealership did the assessment to find out that an O2 sensor was needed. This has been very helpful!

Here are the possible causes of P0303:

Most likely it is the sensor itself.

Hopefully then checked the wiring…

If the problem is actually in the sensor itself so that it needs to be replaced, there is no need to replace them all

An oxygen sensor heater fault is usually a failure within the O2 sensor.

As far as the practice of replacing all of the oxygen sensors at once, I view it as unnecessary.

I have had customers cars in the late '90’s that after replacing one O2 sensor the PCM veiwed the other sensors as slow. The car might come back with a fault like “Slow response from oxygen sensor bank 2, sensor 1”. This occurs so infrequently that I never replace an O2 sensor other than the one that has failed.