Torque Pro Readings on O2 Sensors

[tenro1]

Hi -

Been dealing with the P0420 code now for a month. I replaced the downstream O2 sensor about 2 weeks ago with Denso replacement sensor. Code went away for about 2 or 3 tanks of gas, then came back.

I have not replaced the upstream sensor yet. I did acquire a bluetooth scanner and the torque pro app for android - Hoping someone might know a bit more about this than I do, regarding voltage readings.

On the bank 1, sensor 1 (upstream) O2/A/F sensor, I can get a wide range voltage reading but not a straight up voltage reading.

Exactly the opposite with the bank 1 sensor 2 (downstream) O2 sensor, I can get a straight up voltage reading, but not a wide range reading like the other sensor.

With the engine running, Sensor 1 wide range reading is running between 3.26 - 3.31. Sensor 2 is reading 0 - 0.45.

If I go to test results, and look at the O2 sensors, the #1 sensor is showing what appears to be a static wave at the bottom of the screen. If I try to bring that same sensor up on the top half of the screen - I get nothing. However, I can show the #2 sensor on the top half, and it is not a static shot, rather it moves in seconds as the voltage changes take place.

So, I am trying to understand exactly what I am seeing here, and if both readings are valid.

Any help would be most appreciated.

 

[RS Dude]

Generally you replace both O2 sensors at the same time. Just like you replace both shocks when one is bad, or both tie rods when one is bad, or both wheel bearings when one is bad, or both LBJ when one is bad, or...

See the pattern?

Also, with error codes, the component that the code identifies as being bad, may or may not actually be faulty. The error code only indicates that a component is not working to specifications and may be due to ANOTHER faulty component that is affecting the 'faulty' component. For example: Often someone will get an error message that their Cat is bad, when it usually is a faulty O2 sensor that is causing the fault.

 

[tenro1]

thanks....most of what I have read here regarding the P0420 error code (and i have read a LOT of threads on this)...indicate that most are replacing the downstream O2 sensor, at least at first, though some are replacing both, in some instances just from a maintenance standpoint, so I feel where you are coming from.

So, do you or anyone have any input regarding the voltage readings I was showing in my initial post, or any insight into the Torque Pro app readings I am seeing...? Was just hoping to get some clarity on that if possible.

Thanks again...

Generally you replace both O2 sensors at the same time. Just like you replace both shocks when one is bad, or both tie rods when one is bad, or both wheel bearings when one is bad, or both LBJ when one is bad, or...

See the pattern?

Also, with error codes, the component that the code identifies as being bad, may or may not actually be faulty. The error code only indicates that a component is not working to specifications and may be due to ANOTHER faulty component that is affecting the 'faulty' component. For example: Often someone will get an error message that their Cat is bad, when it usually is a faulty O2 sensor that is causing the fault.

 

[19963.4lsr5]

The upstream sensor will go high low to average a lanmda of 1 or a stoach reading of 14.7 to 1. So you will see it go up and down volts wise. Its the average you care about for the upstream sensor.

The down stream sensor is after the CAT CON and should have very little movement at all and should hang out around .5v that's the sensor that determines if the CAT is working or not. If there is a air leak it will make the sensor read lower than it should and cause bad readings that could produce P codes that may not actually be a problem.

 

[19963.4lsr5]

You have a wide band upstreem sensor. (0-5v) but I think it should go high low. Unless the WB sensors have a built in smoothing circuit.

 

[tenro1]

ok - so, then if I understand what you are saying about the wide band range, then how the scan tool is seeing it is correct, is that correct? And do the voltages I am showing in my initial post seem correct for both sensors to you?

Also - when you say "air leak" are you referring to air on the intake side, or the exhaust side?

Thanks - Michael

You have a wide band upstreem sensor. (0-5v) but I think it should go high low. Unless the WB sensors have a built in smoothing circuit.

 

[19963.4lsr5]

To me they are behaving correctly. However the code is their for a reason. As for air leak it would be on the exhaust side.

 

[19963.4lsr5]

The voltage should be pretty steady for the downstream O2 sensor. Not 0 to .45 oscillation

 

[tenro1]

OK - my thinking is that the range I am seeing on the downstream O2 might be indicative of a faulty sensor. I just replaced this sensor about 2-3 weeks ago, it is a denso part from Amazon, not bosch or other brand. I have yet to do a really comprehensive check on the possibility of a leak on the exhaust, I don't think there is one, but, I am going to do the paper test on it in the next day or so to see if there is something happening with a leak.

Thanks!

The voltage should be pretty steady for the downstream O2 sensor. Not 0 to .45 oscillation

 

[tenro1]

I got some more readings this afternoon -

A/F Sensor B1 S1 - at running temp, revving to 4000rpm 3 times quickly - sits at 3.25 and then rises to 4.50 or higher. Then settles back down to a steady 3.28-3.32 - no wave is showing up in the reading at all. At Idle, the voltage holds steady at 3.25-3.28.

O2 Sensor B1 S2 - at running temperature, at idle, sensor ranges between 0.4 - 0.8. When I do the 4000 rpm test it goes almost all the way down to 0.0 volts while the RPMS are up. When back down to idle, I am showing the 0.4 - 0.8 range.


So - I am concluding that in fact I do need to replace both sensors, up and downstream, as I am seeing no wave on the upstream at all. I am still not convinced the downstream sensor is good or bad, I think it is bad, so to be safe I just set up a replacement exchange with Amazon, still within the 30 days just barely. So, now I guess I gotta order the A/F sensor as well to hopefully resolve this issue.

Is there concurance on these findings, or am I missing something? Please let me know. Thanks!

The voltage should be pretty steady for the downstream O2 sensor. Not 0 to .45 oscillation

 

[19963.4lsr5]

Someone with the newer AF sensor and a scan tool that reads live data needs to chime in. And I'd look at those readings while driving at a steady throttle. Not in park or neutral.

 

[tenro1]

Hi -

Sorry, I forgot to add on my last note that the idle readings you are seeing me quote are also the same basic readings I am getting while driving down the road, at more or less a steady speed.

I had read in another thread somewhere about the 4000 rpm test for the o2 sensiors to get the sensor heaters up to correct temp, so to speak.

So, basically, I am getting one set of readings at idle and driving down the road, and another set of readings with the 4000 rpm test.

Someone with the newer AF sensor and a scan tool that reads live data needs to chime in. And I'd look at those readings while driving at a steady throttle. Not in park or neutral.

 

[tenro1]

One update: the P0420 code set while I was driving and getting these readings this afternoon. I checked the status of the various sensors tests, and even the Cat Converter showed complete.

I am wondering if a test fails, does it show up as failed, or does it show up as complete?

 

[19963.4lsr5]

When your downstream reading goes to zero to me that's bad. That means it leaned out hellishly or the sensor cooled off and was not providing a accurate reading.

And I've never watched a wide band O2 sensor while driving (your up stream AF sensor) to know if it should oscillate like a typical 0-1v narrow band sensor.

 

[tenro1]

Hi -

Well, the thread I was reading about the 4000 rpm test said that the point of the test was to ensure the sensor heater was active and properly heating the sensor, even at running temp. Instruction I believe was to do 3 quick revs to 4000 rpm and check the readings. You saw mine.

I am with you - I don't think it should be bottoming out like that and then going back up the scale to fluctuate between .45 and .80. At either rate, I have a new one on the way from the seller at amazon, he has already sent me a note and told me the new part is heading out ASAP, on their dime.

As for the upstream sensor - my understanding is that the wave form/wide range is the sensor switching between lean and rich on the fuel/air mixture, and that it is supposed to be switching constantly between the two. That is supposed to be constant in regards to the low/high band reading, which I believe means that the wave pattern should be constant. I would expect it to be constant at idle at the very least, and what I am seeing is rather than a constant wave/voltage reading, I am seeing a consistent reading at the same voltage level, which would seem to me to translate into almost a straight line rather than a wave. That is what I am seeing, more or less, when I run a graph against the raw data, with the only real fluctuations taking place when the vehicle is being revved up to 4000 rpm. Then it settles back down to the consistent reading around 3.28-3.30.

Thanks very much for bouncing this back and forth - its been a great help...keep it coming. And if anyone else knows anything about this then please feel free to chime in!

When your downstream reading goes to zero to me that's bad. That means it leaned out hellishly or the sensor cooled off and was not providing a accurate reading.

And I've never watched a wide band O2 sensor while driving (your up stream AF sensor) to know if it should oscillate like a typical 0-1v narrow band sensor.

 

[shadow247]

Forget the scan tool. I see too many techs in my shop relying on the scan tool as a be all end all diagnostic. You need to do the test the factory recommends. That does not include a scan tool. I have posted the diagnostic tree for the PO420 code.

All Data says to hook up a meter, set to OHMS, and test +B and HT. You should see resistance from 11-16 ohms when cold, and 23-32 ohms when warm. The test and values are the same for both sensors. If these numbers check out, then you have a good sensor. Since you've already replaced one sensor, I suggest you do a resistance test on the other.


I am dealing with the PO420 right now as well. I started out with a code for a faulty Upstream or Bank 1 Sensor 1 - PO1135. I replaced the sensor and now I am getting a PO420. I am going to test the resistance on the O2 sensor this evening after I get home from work and report my results. I am hoping it is a bad sensor, as I am moving to Texas and the check engine light will fail the inspection.

 

[IBallEngineer]

Forget the scan tool. I see too many techs in my shop relying on the scan tool as a be all end all diagnostic. You need to do the test the factory recommends. That does not include a scan tool. I have posted the diagnostic tree for the PO420 code.

I get what you are saying, but good scan tools can be in valuable. Now in this case it is common enough of a failure that it should be a straight forward diagnostic with a DVOM. The OP did not specify his vehicle year or engine, but I think he can use this easily enough. As other's stated there is more involved than simply the 02 sensor. I got this from [MENTION=10169]TheDurk[/MENTION], it is very helpful and consolidates those AllData pages in Toyota format.

http://tacoma.site40.net/4Runner_96-02_Repair&Wiring/techinfo.toyota.com/ileaf/02toyrm/02toypdf/02rmsour/2002/024runne/di/eg5vzfe/cip0420o.pdf

:couch2:

 

[TheDurk]

I get what you are saying, but good scan tools can be in valuable. Now in this case it is common enough of a failure that it should be a straight forward diagnostic with a DVOM. The OP did not specify his vehicle year or engine, but I think he can use this easily enough. As other's stated there is more involved than simply the 02 sensor. I got this from [MENTION=10169]TheDurk[/MENTION], it is very helpful and consolidates those AllData pages in Toyota format.

http://tacoma.site40.net/4Runner_96-02_Repair&Wiring/techinfo.toyota.com/ileaf/02toyrm/02toypdf/02rmsour/2002/024runne/di/eg5vzfe/cip0420o.pdf

:couch2:

While the resistance test is definitive in the case of a P1135 (bad heater circuit), it is not in the case of a P0420. The heater may be functioning perfectly, yet the sensor itself (almost always the rear sensor) may have degraded to the point where it sets a P0420. The resistance check only looks at the heater; that's just half the battle, so to speak. It can tell you if the sensor is bad, but it can't tell you with authority that the sensor is good.

 

[shadow247]

While the resistance test is definitive in the case of a P1135 (bad heater circuit), it is not in the case of a P0420. The heater may be functioning perfectly, yet the sensor itself (almost always the rear sensor) may have degraded to the point where it sets a P0420. The resistance check only looks at the heater; that's just half the battle, so to speak. It can tell you if the sensor is bad, but it can't tell you with authority that the sensor is good.

Is there another test for the rear 02 sensor? I checked the resistance and that was fine, so now I am looking at the catalytic converter as a possible source of my P0420 unless you some other diagnostic pages. The only test Alldata gives me is the resistance test. Beyond that, I am still playing around with the Torque app to see my O2 sensor voltage when running.

 

[IBallEngineer]

While the resistance test is definitive in the case of a P1135 (bad heater circuit), it is not in the case of a P0420. The heater may be functioning perfectly, yet the sensor itself (almost always the rear sensor) may have degraded to the point where it sets a P0420. The resistance check only looks at the heater; that's just half the battle, so to speak. It can tell you if the sensor is bad, but it can't tell you with authority that the sensor is good.

See he's all smart and shit! [MENTION=10169]TheDurk[/MENTION]

He backs me up when I run out of smart juice!

:hiding: