Hi Everyone,

I'd like to replace the O2 sensors on my 2001 Mazda Tribute ES V6 3.0L 4WD but I'd like to confirm the following....

Upstream
I need a total of (2) sensors, (1) for Bank #1 and (1) for Bank #2?
Are these sensors the same? I can purchase (2) of the same "upstream" sensors or is there a specific "upstream" sensor for Bank #1 and a specific "upstream" sensor for Bank #2?

Downstream
I need a total of (1) sensor?
This is a specific "downstream" sensor that is different than the "upstream" sensor(s)?

Thanks a bunch for your help....

Have a great day...

 

On the V6, there are four total O2 sensors - two for each cylinder bank. There are three "cats" on the V6, two precats right on the exhaust manifolds and a single lower cat that's fed from the two uppers.

There are two O2 sensors upstream, and these read the exhaust from the engine before it reaches the precats. These two upstream sensors are used by the computer to monitor the air fuel mixture and adjust it accordingly. These two sensors have a direct effect on the performance of the engine.

There are two downstream O2 sensors, one after each precat right at the exhaust manifold. The purpose of these sensors is to monitor the exhaust after it leaves the precats. If the cats are working properly, the PCM will know this by the signal it receives from these two downstream sensors. These two sensors are only used for monitoring the health of the two upper precats and have no effect on the performance of the engine. If you are not getting a catalytic efficiency code, leave these two sensors alone.

There is no O2 sensor monitoring the lower cat. If the lower cat gets weak or goes dead, there will be no code set nor any performance issues,it will act more like a muffler than anything. If the lower cat gets plugged up however, you will have a loss of power.

As far as usage, the two upper O2s are identical to each other, at least electrically. If they have different part numbers it will be because of lead length.


John

 

Hi John, you're AWESOME!!! Thank you VERY much for the detailed reply....

Quick question:
At the time of my original post, I had a P1131 and a P1151 fault code so I planned to replace the (2) upstreams O2 sensors, which I haven't done yet....... but I just got a P0171 fault code.... so should I just replace the (2) upstream O2 sensors (as originally planned for the P1131 & P1151 codes) and clear all the codes and see if I get the P0171 again?

Thanks again... Mark

 

The 1131 and 1151 are indicating a lean condition, one on each bank. Although not impossible, it's highly unlikely both O2 sensors would be defective at the same time. It's more likely that they're accurately reporting an overall lean condition.

Unless you have other reasons for doing so (lots of miles), I wouldn't change the sensors yet.

The first thing to do is remove the MAF meter and clean it (carefully!). There are videos on line on how to carefully remove any dirt or contamination from the sensor. The way the MAF meter works is by monitoring the air moving over a heated wire. If the wire has a coating of dirt on it (insulating it a bit), the MAF meter reports less air than is actually getting into the engine. The PCM lowers the fuel to match the air flow and now you have a lean condition.

If the MAF is clean (or cleaning doesn't improve it), look for a vacuum leak. Any air that's introduced into the engine *after* the MAF is "unmetered", that is, the air is getting into the combustion chamber but the MAF meter didn't measure it and report it to the PCM. Same thing happens; too much air and not enough fuel.

There are a lot of ways of finding leaks (again, videos everywhere). If you can't run it down, a mechanic with a smoke machine will pump white smoke into the engine. Any and all places that can cause leaks will leak smoke out of them (a smoking gun if you will).

John