o2 sensor waveforms

[justinf89]

I've been getting p0420 code for a while now so today I decided to graph the o2 waveforms for my safari. I thought the p0420 code is thrown when a pre cat o2 sensor is close to the post cat sensor. Can anybody tell me if the sensors are doing ok? This is at an idle. The pre cat waves don't look too good to me.

 

[NJC]

I also had idle O2 sensor failures (sensor vents obstructed - clogged) that had wonky and noisy waveforms too. Bank 2 is quite noisy.

 

[dparm]

Bank 2 isn't as "clean" looking as bank 1 but I'd hardly call it a problem. IMO, clear the code and see how fast it comes back. Has gas mileage dropped?

You can also clean the sensors with electronics cleaner.

 

[crw]

This is a bit of a smart-alec answer, but we need to know what they "should" look like. Generally, I'd think that waveforms moving around are good, and waveforms that are fixed are bad. But honestly I don't know... I would like to hear from an expert.

 

[mattd]

pre cat sensor waveforms are good. It looks like the B1S2 is flatlined, little to no response. When post cat 02 sensors mimic pre cat sensors, the PCM will flag a cat efficiency code.

Also, you cannot judge these readings at idle. Best is cruise @ 2000 RPM. Or, idle 2500 RPM. take readings then.

 

[Vikas]

What is on x-axis? Is it in seconds?

 

[justinf89]

Alright thanks guys for the ideas. I'll take them both off and see if they are clogged up/dirty. I believe the x-axis is milliseconds because it moved pretty quick. I'll post back with 2k rpm readings after I take them out to check them.

 

[NJC]

Justin, fwiw here are the pics of the waveforms that came off of my failing (idle only) Bosch sensor. My theory is the white powdery material caused enough of an exhaust obstruction to provide poor idle readings. Once the exhaust stream was faster, the sensor responded correctly.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1427640

 

[Trav]

Bank 1 sensor 1 at 0.145 is below 0.2-0.8 which is the normal range. Whats the fuel trim?
Check the air check valve on bank 1 or an exhaust leak before the O2.

 

[Vikas]

The ECM looks for the difference in cross counts of the front and rear O2 sensor more during the deceleration i.e. when you lift your feet off the gas while going steady at highway speed. If you can get the scanner to record during that period, you might see that both rear and front O2 sensor for the bank one shows similar waveform and that will explain your P0420 code.

By the way, your pre-cat waveforms are fine as far as I can ascertain.

Google oh two sensor extension and you will know what to do

- Vikas

 

[Trav]

Quote:
Google oh two sensor extension and you will know what to do



Yep you got that right LOL.

Still O2 1 maybe almost flat lining on decel. Those check valves on the pulse air system are notorious but not a big deal, they are cheap to replace.

I'm thinking no O2 codes present so its possibly something effecting just bank 1 which leads me to an exhaust leak before the O2 or the pulse air check valve. Any thoughts?

 

[Vikas]

I just realized. OP has only single rear sensor. We need to ignore the non-graph in the 4th quadrant.

I do not see huge difference between bank1 vs bank2 primary sensor output. Assuming the timescale of milliseconds, one will not find a switch point of the secondary sensor in such a short duration.

In short, the enclosed data is inadequate to show any problems. A longer snapshot could give more hints. The bank 2 is not as regular as the bank 1 but without more information, the data is not enough to convict the bank 2 sensor.

Which car? Which scanner? This looks like a good software and seems as if your vehicle supports high scan rate.

- Vikas

 

[Trav]

Parts catalog is listing a downstream left and right for an 04, it would make no sense to use a upstream on both banks with a single down stream. In that case on a V engine the primary O2 is usually right before the cat or in the rear of the crossover pipe after it leaves bank 2 e.g. Gm 3800.
Not saying it isnt i just never saw it done that way.

I was looking at the wrong year, this one doesn't even use a check valve. Sorry my bad.
Can someone explain the 0.145v on bank 1 sensor 1?

 

[NateDN10]

Originally Posted By: Trav
Can someone explain the 0.145v on bank 1 sensor 1?

To me it looks like the voltage in the upper left of each graph shows the most recently sampled reading.

Both banks 1 and 2 show swing from ~0.1V to 0.85V in the graph view.

 

[Trav]

Thanks that's it, it must just be where it happened to be when it took the snapshot right not long term?

My apologies, i am sick as a dog and cant even think properly i shouldn't even be trying to post.

 

[justinf89]

Small update. I removed the two upstream sensors today(don't know which is which) and heres a pic. Both were white but I wiped the left one off with my finger. What could cause them to be white like this? I read on the internet that it could be running lean. I'll check the fuel trim when I measure them again. I'm going to soak them in some kind of cleaner and measure them again. I'll post back later.

 

[mattd]

white is caused by a lean condition.

 

[justinf89]

Ok well I re-installed the sensors and went for a drive and immediately got p0420 code. I got back home and checked the waveforms and they were both much cleaner but at 2k rpm, it's clear the converter is shot. The after converter sensor went crazy anything past idle. Oh well, at least I know what's really wrong now.

 

[Vikas]

If you don't get OEM converter, your will be getting P0420 back again with 6-12 months.