Hi all,

My CX5 recently got the P0137 code - Oxygen Sensor Circuit Low Voltage (Bank 2, Sensor 2). I connected BlueDriver to see the live data, and the downstream sensor has the voltages from 0.01 to 0.035V, mostly at 0.02V. (I believe it should normally be ~0.45V)

I thought it was the O2 sensor that's gone bad and I replaced it, and still has exact same issue. I have not further diagnosed it but I figured it could be circuit and maybe the 12V coming into the sensor is bad? Could this be caused by something else?

Thanks in advance for your help!

 

Welcome to the forum

 

A general response first:

Just because you get a DTC and you look on the internet what it is don't assume that is the part and fault. There are very vey time that it is that simple.
DON'T REPLACE PARTS before first checking and double checking that it is failed. Replacing random parts thought to be the problem can and often does slow down the actual finding of the DTC as well often can create added issues.

If you get a DTC(s) there are "SEVERAL" things to check and rule out and not the internet information using the word "OFTEN" . Do the diagnostic work first and confirm that the part you suspect is in fact the issue.

As for the DTC P0137 code there are several things to think about having to do with this. And No, I hate to pop the bubble on readers that rely on internet information to become DIY Automotive Diagnostic Technicians (lol) the HO2 is generally not the original cause of that DTC . Go and follow the diagnostic tree and do ALL the work and you WILL find the cause of that DTC.

Or wait for the dozen or so responses next that will help you "GUESS" what part top change next to solve the problem! $$$$

ASE

 

update: I got through the issue and passed the emission test, and wanted to share it in case if anyone else runs into this.

So later on, by looking at the live data while driving, I found out that my downstream O2 voltage was fine (0.7-0.9V -ish) when I stepped the gas. But as mentioned, it was very low (~0.02 V) when it was stopped and idle. When I was driving and wasn't stepping on the gas, it was also very low.

Since I did replace the O2 sensor already, it was not likely the O2 sensor itself. Also, since the voltage was indeed changing, it was probably not a wiring issue.

A very low voltage (0.02V) means that the gas was very lean - or a high percentage O2. Since it was only like that when I wasn't stepped on the gas, I thought it could be leaks right before or near the downstream O2 sensor causing it, which means when I stepped the gas, since there was more exhaust air flowing out, the leak didn't matter for the O2 content; but when the car was idling, the O2 content would be close to ambient O2 content, causing the low voltage.

So I checked out under the car, and saw that right before the downstream O2 sensor, there were big leaks in the bolted connection right before the second cat (the TWC). Basically the gasket was probably gone and I could feel the air leaking out big time when the engine was on.

A permanent fix would of course be replacing the gasket but I was running out of time to pass emission so I just put some exhaust leak sealer.

After that, at idle, the downstream O2 sensor's reading is now steady at ~0.8V (yay). When I drive, it is still about 0.7-0.9 V when I press the gas, and when I'm not pressing the gas (but the car is moving), it goes to 0.0V. I think maybe that's by design, because I do not get the code or check engine light after the cycle completed, and was able to pass the emission. So I'm good for two years

 

Nice work.
It only takes a small amount of oxygen in the exhaust after a CAT to cause a DTC. Most of the time the exhaust leaks are large enough that you can hear them especially during cold starts because fueling is richer and effects the noise level of exhaust. Also a driver many times will smell exhaust in the cabin at least the driver should?
Now we just need you to call the part by its correct name. HO2
The H (heated) is important because it became part of supporting to lowering emissions during the start-up period of a cold engine.