2011 Equinox V6 O2 Sensor High Voltage

I was doing some testing on a 2011 Equinox following procedures in the book. Car runs fine and scan data looks good, but the bias voltage on all O2 sensors when cold or disconnected is 1.9 volts. When running the scanner is showing going up and down between .04 and .09. When I connect to my scope the reading goes between 1.04 and .9. Something I’m doing wrong?

Ken

Are you dealing with a standard zirconium O2 sensor or with a wideband air/fuel ratio sensor?

Zirconia Oxygen Sensors I believe.

wrote:

When running the scanner is showing going up and down between .04 and .09. When I connect to my scope the reading goes between 1.04 and .9. 

Where is the scope leads hooked up to? Also did you mean to write .04 and .9 volts?The computer is sending out 2.9 volts on the signal wire and 1 volt on the ground wire. If you put your scope to battery negative and take direct readings at the sensor I believe this is what you'll find. The voltmeter inside the computer is reporting the difference in potential between the signal and ground, 2.9 volts minus 1 volt so this is where 1.9 volts comes from.

Working with the idea that nothing is wrong with this engine, the data suggests to me that you're looking at a/f sensors. A/F sensors don't work the same as standard 02's rather the change from lean to rich is measured in small current amounts as you show. Ref voltage values are different for each manufacturer. I believe GM is 2.6v. The current value change of .04 to .09 would be consistent with normal switching. What's got me is the 1.9v reference voltage. Maybe the Equinox has 1.9v ref instead of 2.6v.
1.04 would be lean and .9 rich as 1 is stoich.
But the other thing is the downstream 02's. I haven't read anything suggesting that A/F's are being used there. Standard 02's are the norm. But?
If I missed your point, let me know.

wrote:

the data suggests to me that you're looking at a/f sensors.
 

According to Service Information, they are not a/f sensor. They are regular standard zirconium O2 sensors.
 

Have to ask, is your scanner showing an equivalency ratio PID on global?

To start with I do not believe they are A/F sensors. Throughout the service manual (Mitchell) it only references HO2S Oxygen Sensors, no mention of A/F sensors.

I am going to start the testing with a cold engine.

With key on and engine off, this is a screenshot of my Autel MS906TS scanner. I cutoff the Unit column, but that is V for volts.
 

I also attached an excerpt from the Mitchell Manual.
 
 
  
I will next measure the voltages directly at the sensor B2 S1.

Ken



  

Ok, things are starting to come together and make a little more sense. 

I got a little confused with the connections between the sensor's floating ground controlled by the ECM and the chassis ground.

With engine cold, key on, engine off I took readings at the sensor with DVOM.
 
PPL\WHT High Reference to chassis ground = 2.78 volts
Tan\WHT Low Reference to chassis ground  = 1.04 volts
PPL\WHT High Reference to Tan\WHT Low Reference = 1.80 volts.

These readings appear to be inline with the specs in the manual. Of course the scanner is still showing 1.9 volts. Since I am taking the readings directly at the sensor, I am thinking that this may be a slight voltage drop in the harness between the ECM and the sensor.  Thoughts?

I am now going to take the readings with the scope with the engine running and compare to the live data on the scanner. I'm thinking that everything will fall into place when I have the probes on the sensors floating ground instead of chassis ground. I'll do it both ways.

Thanks for the replies, it always help to sound thing out.

Ken

Ken. You have peaked my courosity on this. GM has always had a 450mv bias voltage for 02's on its signal wire. Wiring integrity test has been to unplug the sensor. If the scan data remains at 450mv, wiring is good.
This is a 2011 Chevy Equinox with a 3.0l V6 engine?
Please let us know which O2 wire you're hooked up to and post those readings.

Ok, this might go off topic a bit, but I am actually learning a lot from this one test. Which is why I think testing is very important to do on know good vehicles.

I have found that if you connect your scope/DVOM to certain connections, such as the O2 Sensor's high reference and the probe's ground lead to ground, it changes the voltage readings shown on the scanner. In my case it dropped from 1.9 volts on the sensor to .75 volts when connected the DVOM.

I also observed that the voltage reading from the scope is different than the voltage reading from the DVOM, must have something to do with the resistance in the probes.

Bottom line is you need to know how different connections and floating grounds can affect the readings.

ScannerJohn, now that I know some of the problems I was having with connections and probes, I will rerun the tests and post the results here along with what probe is connected to what wire.

Thanks,

Ken