O2 Sensor OBDII Info

[cnl390]

Forgive me, I know this has been asked, re-asked & asked again. But a search turns up too many threads to wade through.
When reading live or freeze frame info what should I be looking for when it comes to diagnosing O2 sensor and cat performance?
And over all are there any other readings I should monitor regularly?
Thanks for the help.

2006 4Runner
OBDLink LX scan tool

 

[paperchasin]

Generally speaking, your front O2 sensor should oscillate in voltage from high to low quite frequently/rapidly, as the front O2 sensor is primarily used to control fuel trim, both short term and long term. The secondary/rear O2 sensor though serves to determine catalytic converter functionality, in most cases, cat efficiency (oxygen storage). When you have a fully functional cat, the rear O2 sensor should stay nice a steady (actual voltage will vary depending on driving conditions). However, if you have a faulty/non-functioning cat, you will see the rear O2 sensor readings mimic, or follow, the front O2 sensor, maybe lagging by a second or so. Hope this helps.

 

[cnl390]

Generally speaking, your front O2 sensor should oscillate in voltage from high to low quite frequently/rapidly, as the front O2 sensor is primarily used to control fuel trim, both short term and long term. The secondary/rear O2 sensor though serves to determine catalytic converter functionality, in most cases, cat efficiency (oxygen storage). When you have a fully functional cat, the rear O2 sensor should stay nice a steady (actual voltage will vary depending on driving conditions). However, if you have a faulty/non-functioning cat, you will see the rear O2 sensor readings mimic, or follow, the front O2 sensor, maybe lagging by a second or so. Hope this helps.

Thanks for the reply. I am new to this and am trying grasp all this vast amount of information.
I will be driving around town in a few minutes and will check the real time voltages.
On my freeze frame data from this morning I have these readings.
O2 voltage Bank 1 Sensor 2 0.62 V
O2 voltage Bank 2 Sensor 2 0.2 V
O2 voltage wide range Bank 1 Sensor 1 3.3 V
O2 voltage wide range Bank 2 Sensor 1 3.42 V

Another question I have is the Catalyst temperature
Bank 1 Sensor 1 1436.18 F
Bank 2 Sensor 1 1436.18 F
Bank 1 Sensor 2 1253.30 F
Bank 2 Sensor 2 1253.30 F
I know I am new to this, but it seems odd that the temps for bank 1 & 2 are exactly the same.

 

[paperchasin]

Thanks for the reply. I am new to this and am trying grasp all this vast amount of information.
I will be driving around town in a few minutes and will check the real time voltages.
On my freeze frame data from this morning I have these readings.
O2 voltage Bank 1 Sensor 2 0.62 V
O2 voltage Bank 2 Sensor 2 0.2 V
O2 voltage wide range Bank 1 Sensor 1 3.3 V
O2 voltage wide range Bank 2 Sensor 1 3.42 V

Another question I have is the Catalyst temperature
Bank 1 Sensor 1 1436.18 F
Bank 2 Sensor 1 1436.18 F
Bank 1 Sensor 2 1253.30 F
Bank 2 Sensor 2 1253.30 F
I know I am new to this, but it seems odd that the temps for bank 1 & 2 are exactly the same.

Can you please clarify where/how you obtained this freeze frame data? Do you have CEL currently?

Regarding catalyst temperatures, my understanding is that our cars do not actually have temperature sensors for the catalyst and that those temperatures are based off a model that Toyota uses in their software for estimation purposes. If this is indeed the case, that is why the temperatures are the same for both banks, and is slightly cooler for sensor 2 because it is simply further away from the engine. Someone please correct me if I'm wrong.

 

[fullboogie]

You should also monitor short term fuel trims, because their fluctuation can be indicative of how or if the O2's are performing properly. Generally as long as the STFT's are fluctuating in the plus or minus 10% range (-10% through +10%) then you are OK. Ideally, you would want more in the 5% range. The point is that if you have a problem with either the upstream or downstream O2 sensors, the ECU (or PCM or whatever the Toyota world calls it) is getting incorrect feedback, and your fuel trims will go haywire.

 

[cnl390]

Thanks for the help, I really appreciate it.
I had a CEL, VSC Trac lights on fro a couple of days but they were off when I drove it a few minutes ago. This has been happening for some time.
Freeze frame data was from an OBDLink LX bluetooth scan tool using the OBDLink app. Freeze farme was done at 56.54 mph, 1748.25 rpm.
Short term fuel trim % Bank 1 0%
Long term fuel trim % Bank 1 1.56%
Short term fuel trim % Bank 2 -3.12%
Long term fuel trim % Bank 2 3.12
Short term fuel trim Bank 1, Sensor 2 99.22%
Short term fuel trim Bank 2, Sensor 2 99.22%

 

[fullboogie]

Those look good to me.

 

[Ralph Blake]

So in truth the o2 sensors are there to make sure the Cat is working 100% right? And as far as gas mileage of performance it has zero effect.

So why should i spend hundred's of dollars to replace the sensors? And this is if they really are defected.
Who really knows if these codes really mean anything, we do know the Toyota service Dept. service writers will just say you need to replace them.

Anyone ever visit their dealers service Dept. and ask if something needs to be fixed,and had a service writer tell you NO everything is "A" OK. Anyone?

Believe this or not,when the wife and i went to our Toyota dealers service Dept.s open house a few years ago.

A service writer stood up and told everyone they were on "COMMISSION" i mean you should have seen, the look on everyone's face.
Now that sure told me and everyone else something.:flamethrwoer2:

 

[fullboogie]

The downstream O2 tells the ECM if the cat is "working" but the upstream does provide data to the ECM that changes how the spark/fuel tables are calculated. If your upstream sensor goes bad, ECM's on most makes/models will go to the "failsafe" tables for extra protection of the engine - meaning very rich a/f ratios and minimal spark advance. In other words, worse fuel economy and worse performance. I am assuming this is true for Toyota as well.

 

[Ralph Blake]

The downstream O2 tells the ECM if the cat is "working" but the upstream does provide data to the ECM that changes how the spark/fuel tables are calculated. If your upstream sensor goes bad, ECM's on most makes/models will go to the "failsafe" tables for extra protection of the engine - meaning very rich a/f ratios and minimal spark advance. In other words, worse fuel economy and worse performance. I am assuming this is true for Toyota as well.

Have you or anyone reading this thread,had their gas mileage drop and it was traced directly to a defected o2 sensor?

 

[fullboogie]

Have you or anyone reading this thread,had their gas mileage drop and it was traced directly to a defected o2 sensor?

Yes. Have you ever monitored OBDII PID's to see how a defective O2 sensor affects short term and long term fuel trims, and spark advance? What were your observations?

 

[BlackWorksInc]

Those are not O2 Sensors, most modern Toyota run AFR (Air Fuel Ratio) sensors upfront and Traditional Heated O2s in the rear, that's why you're seeing 3v on both Sensor 1s

 

[Ralph Blake]

Yes. Have you ever monitored OBDII PID's to see how a defective O2 sensor affects short term and long term fuel trims, and spark advance? What were your observations?

All i know is when my check engine light came on,they ran a code check and told me my o2 sensors were needing to be replaced. My gas mileage had not dropped and my engine was preforming as well as ever. That was five years ago the light is still on, and gas mileage had stayed the same in town and on highway,the engine is still preforming well. Hey i got quotes of $500 and $800 to replace them. Now this was not on my 08 V6 2wd 4Runner. it is my other older v6 auto.

 

[fullboogie]

Those are not O2 Sensors, most modern Toyota run AFR (Air Fuel Ratio) sensors upfront and Traditional Heated O2s in the rear, that's why you're seeing 3v on both Sensor 1s

Black - are those true widebands? I.e. Bosch LSU's?

 

[BlackWorksInc]

Black - are those true widebands? I.e. Bosch LSU's?

As far as I know the Denso units seem to be a wideband. The data output by them is read as Lambda figures vs. simple voltage variances (well at least the ECM is extrapolating the data as a lambda reading.)

Post Note-
[MENTION=121692]Ralph Blake[/MENTION]

The reality is it is slightly more intertwined than a simply watching the Catalyst. The AFR/O2 Sensors are used to monitor Catalyst efficiency, but they are also used to adjust fuel mapping, injector pulse width, ignition timing, and engine operation in response to real world variables (ultimately this is to keep the Catalyst "happy" and functioning correctly; but as a result of that the vehicle operates in it's peak power and efficiency state as well.)

Without the sensors, the vehicle would not be able to dynamically respond to variances in air, fuel, and/or spark delivery and it would not run as well (thus less power, less fuel efficiency, and more emissions.)

I actually had some information talking about how Post Catalyst O2s actually control more of the vehicle's fuel trim than the manufacturers admit they do (in some cases causing contradictory DTCs to pop up)... but I can't seem to find out that information...

 

[fullboogie]

As far as I know the Denso units seem to be a wideband. The data output by them is read as Lambda figures vs. simple voltage variances (well at least the ECM is extrapolating the data as a lambda reading.)

WOW - that's surprising. Ford didn't come out with that on the Mustangs (or any other model that I am aware of) until just a few years ago. Good for Toyota!

 

[paperchasin]

I actually had some information talking about how Post Catalyst O2s actually control more of the vehicle's fuel trim than the manufacturers admit they do (in some cases causing contradictory DTCs to pop up)... but I can't seem to find out that information...

I'd be curious to read more about this too.... especially the part regarding conflicting DTCs.

 

[BlackWorksInc]

I'd be curious to read more about this too.... especially the part regarding conflicting DTCs.

Basically, there's a thing that Toyota has in their Data List called "Total Fuel Trim" (I've really only seen this PID in the TIS Techstream, a lot of generic OBDII tools don't seem to pick this up) if you know how to decode it (It's basically ST + LT and the left over that makes the number theoretically is the Downstream O2 Fuel Trim; but I don't remember for sure.)

I actually saw a really interesting experiment where an instructor used an old Dodge caravan and rigged the rear O2 to be pinged very Rich. The ECM dropped injector pulsewidth drastically and the front O2 read extremely lean, but since the rear O2 was pegged Rich it continued to ignore the front O2 that was screaming how lean it was. After a while it even threw a P0172 (Bank 1 too rich) despite evidence from the front O2 stating otherwise.

I saw a similar effect in a Toyota case study from the same instructor that showed a real world version of this occuring. The rear O2 was biased enough that it didn't outright set a DTC, but it was manipulating fuel trim enough to cause drivability issues and a counter-intuitive DTC. The instructor showed us how to use Total Fuel Trim to determine how much the rear O2 was adjusting fuel trim.

This is apparently something that is present in other brands, but you may not be able to see a data list PID for it (I believe he mentioned that either Ford or Honda have no actual PID for the downstream FT.) But most manufacturers say that it won't adjust more than 4% anyways, so it shouldn't be an issue; real world testing seems to indicate otherwise.

 

[cnl390]

As far as I know the Denso units seem to be a wideband. The data output by them is read as Lambda figures vs. simple voltage variances (well at least the ECM is extrapolating the data as a lambda reading.)

Would you know why the scan report doesn't have any reading for Sensor 2?
O2 sensor lambda (Bank 1, Sensor 1) 1.01
O2 sensor voltage wide range (Bank 1, Sensor 1) 3.33 V
O2 sensor lambda (Bank 2, Sensor 1) 1.01
O2 sensor voltage wide range (Bank 2, Sensor 1) 3.33 V
O2 sensor lambda wide range (current probe) (Bank 1, Sensor 1) 1
O2 sensor current wide range (Bank 1, Sensor 1) 0.02 mA
O2 sensor lambda wide range (current probe) (Bank 2, Sensor 1) 1
O2 sensor current wide range (Bank 2, Sensor 1) 0.02 mA

 

[BlackWorksInc]

Would you know why the scan report doesn't have any reading for Sensor 2?
O2 sensor lambda (Bank 1, Sensor 1) 1.01
O2 sensor voltage wide range (Bank 1, Sensor 1) 3.33 V
O2 sensor lambda (Bank 2, Sensor 1) 1.01
O2 sensor voltage wide range (Bank 2, Sensor 1) 3.33 V
O2 sensor lambda wide range (current probe) (Bank 1, Sensor 1) 1
O2 sensor current wide range (Bank 1, Sensor 1) 0.02 mA
O2 sensor lambda wide range (current probe) (Bank 2, Sensor 1) 1
O2 sensor current wide range (Bank 2, Sensor 1) 0.02 mA

Either your scantool is acting up or there is an additional page/section for more data; you're first page shows that it picked up Bank 2 Sensor 2 data fine.