I have been playing with the Android Torque App data logging. I am trying to see whether I need to replace my O2 sensor(s) and I thought this would be an interesting test. I know roughly how the sensors work, but I don't have a good feel for what the readings should look like. I could not find the right combination of search terms to let me find out either. So, here goes.

Here are my readings from a cold start (and I started logging before I started the car). Can anyone tell me what this means?

I have been told that there should be a roughly constant back-and-forth to the readings. Based on that, I am wondering if Sensor 1 is OK and Sensor 2 is bad because:

• Sensor 1 is a fairly constant up and down of roughly equal magnitude.
• Sensor 2 is stuck and out of range (above 1 volt) at the beginning.
• Sensor 2 seems to hang on the higher end a few other times as well (columns J-M and T-W in the picture).

I was thinking of replacing them anyway, but it would be nice to know that I was doing it because it was needed as opposed to some of the preventative maintenance that I do. Also, I think this stuff is interesting and if someone could confirm what I am thinking or tell me I am completely off base I would appreciate it.







Sorry for the giant image.

Thanks,
Chris

 

If you are not getting any O2 sensor (P0141) codes from the ECU, my best guess is that they most likely are functioning within reason. However, I've been known to be wrong. How many miles are on the car?

I think it is interesting as well and wish I could contribute more; however, it is far beyond my scope.

With that said, I had an O2 sensor code embed, as a result of a check engine light, for the front bank, IIRC, a few years ago. The computer does a pretty good job at letting you know if something is wrong. It just popped up one day driving in hellish summer FL heat stop and go traffic. The car had around 110k ish miles on the odometer. I just purchased two new Denso's from Amazon and replaced them both at the same time when the code appeared, have not had any problems since.

 

That's great info, Zeta, thanks! I should have included that. It is an '03 CL-S with just shy of 140k miles. I have not gotten a code or a CEL from it, I was just realizing it was getting pretty high in miles and pretty low MPG. (I'm getting 15mpg, but that is almost 100% high traffic city driving.)

Thanks also for the thoughts on the sensors. I wasn't sure how much latitude the sensors had before giving me the P0141, and whether a new, good sensor would perform measurably better than one that might be *just* good enough.

And then there's the fear of how much of a PITA it will be to get 12 year old 140k mile O2 sensors out of their homes...

 

lol, no problem. Relatively speaking, and knocking on wood at the same time, I have not had many codes to speak of during my ownership of this car. I've been running the supercharger since around 44K miles (currently 148K) and if anything 'rears its head' I'm usually on it pretty quick.

It may be prudent, though, to just replace the O2's at your 140K mileage interval. As you mention, they are 12 years old. RockAuto has a good price for Denso 2344621($22.79) and 2344727($42.89). They have a coupon for 5% floating on the web for further savings.

The hardest part, when I did mine, was getting at and disconnecting the front O2's electrical connector. There is enough room to get to it; however, when doing it on your back, positioning can be awkward, but doable. Before doing any work, though, make sure to soak the old O2's at the pipe with a good penetrating oil/spray, like seafoam deepcreep, and let it sit. Usually, you can rent the o2 socket from a local parts store. Make sure to pick up a little packet of never seize or equivalent and place a little on the threads before installing the new O2's. Being careful not to get any on the sensor ends.

Also, you may want to clean your EGR ports if they have never been touched. They tend to get pretty built-up with char after awhile. Do a search here on the forum, there are plenty of threads related to the subject, if interested.

 

As a general rule OBDII O2 sensors should be replaced at around 100K miles per O2 sensor manufacture.

 

the secondary O2 on/behind the cat only tells you if the cat is working properly. So don't bother touching that one.

 

^ Its was only $23.00?

 

Thanks, guys. I have actually had those denso sensors in my Rock Auto cart for a few days now. I think I'll go ahead and pull the trigger on them since they are so old. To be fair, I don't try to diagnose my spark plugs before changing them. I just change them on schedule (ok, more or less on schedule...)

Thanks again, Zeta for the tips on pulling the old sensors.

For the hell of it, I can also try logging again after I change them to see if it is visibly different.

I'm still curious about whether anyone can explain what to look for when diagnosing these things. The few articles I could find online mostly describe how they work, but not much about how to tell when they have had it.

Thanks again,
Chris

 

They are suppose to test between .1 to .9 volts and reads 2 to 3 times per second.

Sorry can't read the graft from phone.

 

Thanks for the verification, 01acls. Do you know if having a sensor go beyond that range is an indication that something is definitely wrong? Again, just trying to understand these things better.

 

Correct, out of spec means wrong/defective... replace O2 sensor.

What happens is they get slow/lazy or read wrong by sending the wrong volts.