Video of 02 Sensor Readings, Need Help Understanding

[rdiggidy]

My 2002 Camry (with 130,000) has had the check engine light going on and off every few days for the past couple weeks. So today I pulled the codes and got: P0420

So it looks like I'm either going to need a new CAT or new O2 sensors. I have a OBD II program that hooks to my laptop, so I ran the program while monitoring the O2 sensors in hopes of figuring out if I need a new CAT or new O2 sensors. I'm not really understanding the readings. Can you guys make anything of this video (if you watch it in 720p the numbers are clear enough to read):

You Tube

You Tube

Here is the readout given when the code was pulled:



Is that enough info for anyone to give me an idea of which direction I should be going (O2 sensors or new CAT)?

Thanks for the help!

[Mister_Perkins]

Did you maintain 2500 RPM for 90-120 seconds before recording the video? If not, re-do your test

[rdiggidy]

Car was warm and I was driving.

So do it again:

1. Idle car for a couple minutes at 2500 RPM's
2. Record
3. Continue idle at 2500 RPM's for video?

If so, I'll get on it.

[Mister_Perkins]

Yep . you may not get a correct reading for O2S B1-S2 if your idling

Confirm that the display of ”O2S B1 S2” changes between 0V to 1V with the engine speed at 2,500 r.p.m

You can also physically inspect the oxygen sensor by disconnecting the harness and measuring the resistance between (HT) and (B+).. should be between 11-16 Ohms at 68 degrees. (HT) And E1 should have no continuity also



From looking at your data at the bottom though, your fuel trims seem to be in an acceptable range.. Should be +/-10% ... 0 being perfect.

I can tell from watching the video though , your Bank 1 Sensor 1 is working properly. See how it only has a fluctuation of only around 1%?? This is a good thing. Your B2-S2 though drops to 0.00v at one point, indicating theres a fault or a short.

I think there may be a problem with B2-S2, but i would confirm it by testing the resistance on the Sensor with the image above

[rdiggidy]

That was poor wording on my part (didn't mean to use the word idle).

Just to be sure I've got it right. Car in Park, rev to 2500 for test?

[rdiggidy]

B1-S2 is at .760 V when idling. When I revv to 2500 RPM it drops momentarily to 0V then goes to about .400 V (though it is varying between .400v and .650 while I'm holding it steady at 2500 RPM)

[Mister_Perkins]

I would say your B1-S2 is shorting out. It shouldn't drop to 0.0V. Test the resistance / replace if not within 11-16 ohm.

I have to get off here though , I will be back on tomorrow morning . PM me if you have any more questions

[rdiggidy]

I'll try to find my voltmeter and test it.

Thanks for the help!

[rdiggidy]

B1-S2 is at 14 ohm.

Would you still go ahead and replace B1-S2?

[rdiggidy]

I ended up ordering the upstream (S1) and downstream (S2) sensors, figured I might as well replace them both if one is having problems, the other probably isn't too far behind.

The day after I ordered them, I decided to disconnect the upstream sensor and see what the resistance on that was (not sure if it’s suppose to be the same as the down stream, but thought I’d just do it to see). Well the upstream was about 1.3 OHM’s (not sure if that’s good or bad for that sensor) When I plugged the upstream sensor back in, the check engine light went out.

It’s been about a week (and about 300 miles) since the light went out and the check engine light is still off???

So today I hooked the OBD II back up to have another look at the sensors voltage. The video below is taken after the car is warm, the car ran at 2500 RPM’s for about 120 seconds before this video, and is running at 2500 RPM's during the video.

At about the 35 second mark on the video I take my foot off the gas, let the car idle for a a few seconds and then at about the 44 second mark I accelerate back to 2500 RPM’s. When I accelerate back to 2500 RPM’s you can see S2 drop down to 0 Volts for an instant before going back to about .720V

You Tube

You Tube

Any thoughts?

The sensors were about $180 for both, which I don’t mind paying if they are the problem. But now I’m a little hesitant to put them in. If they aren’t the problem, I’d rather return them and save the $180 and put that towards whatever the problem is.

Any chance “bad gas” could have been the culprit? Right now I’m thinking I’ll just wait a little while and see if the check engine light comes back on, as all seems to be running fine for the moment (including gas mileage being about average).

Thanks for any help!

[fenixus]

yeah, go ahead and change that post-cat (downstream / rear) oxygen sensor first. voltage drop to 0V is not normal, it shouldn't say 0.00V ever, however numbers like 0.07V are not uncommon for worn out sensors. yours almost flat lines on RICH side (above 0.6V) and stays there forever (it should be oscilating rapidly between less than 0.45V and above 0.6V or so. at same time your upstream (wideband) AFR sensor shows it's OK (3.3V and around that).

that sensor it the only way computer knows if CAT goes bad or not, so if sensor itself is seriously worn out (without throwing a code for it yet) then most likely ECU will assume the CAT went bad as it compares oxygen readings before and after the CAT in exhaust stream.

IIRC P0420 basically means there is not much difference in oxygen levels in exhaust stream before and after CAT, so it assumes the CAT doesn't do its job.

replace the sensor with Denso OE (it's same as OEM) from ebay or amazon at like $60 shipped free. check part number on densoaftermarket.com and go from there. there is a chance the CAT still works, but the computer can't see that.

those narrow band ixygen sensors usually do not last much longer than 100k miles. AFR sensors usually are done by 150k miles.

P0420 has only 3 problem areas and last one (mentioned by Perkins) is a shorting out wiring, so also check the wiring, at least visually for any cracks in insulation, but most likely the sensor itself is bad (its readings are bad).

[rdiggidy]

Originally Posted by fenixus

yeah, go ahead and change that post-cat (downstream / rear) oxygen sensor first. voltage drop to 0V is not normal, it shouldn't say 0.00V ever, however numbers like 0.07V are not uncommon for worn out sensors. yours almost flat lines on RICH side (above 0.6V) and stays there forever (it should be oscilating rapidly between less than 0.45V and above 0.6V or so. at same time your upstream (wideband) AFR sensor shows it's OK (3.3V and around that).

that sensor it the only way computer knows if CAT goes bad or not, so if sensor itself is seriously worn out (without throwing a code for it yet) then most likely ECU will assume the CAT went bad as it compares oxygen readings before and after the CAT in exhaust stream.

IIRC P0420 basically means there is not much difference in oxygen levels in exhaust stream before and after CAT, so it assumes the CAT doesn't do its job.

replace the sensor with Denso OE (it's same as OEM) from ebay or amazon at like $60 shipped free. check part number on densoaftermarket.com and go from there. there is a chance the CAT still works, but the computer can't see that.

those narrow band ixygen sensors usually do not last much longer than 100k miles. AFR sensors usually are done by 150k miles.

P0420 has only 3 problem areas and last one (mentioned by Perkins) is a shorting out wiring, so also check the wiring, at least visually for any cracks in insulation, but most likely the sensor itself is bad (its readings are bad).

Thanks! I'll change it out!

I got the Denso A/F and O2 sensors off Amazon (looks like it was actually $165 for both). I checked Ebay, they didn't have it any cheaper than Amazon. I'll get them both taken care of at once and be done with it.

Thanks for the help!

[Mister_Perkins]

Yup ^

Fenixus is a smart guy, thanks for plugging in on here bud

[fenixus]

no probs and good luck!

[coffee-3000]

Originally Posted by fenixus

it should be oscilating rapidly between less than 0.45V and above 0.6V or so

fenixus, what is the acceptable range ? Less than 0.45V and greater than 0.6V ? How much less than 0.45V and how much greater than 0.6V would you guess ?