How to quickly test an oxygen sensor circuit (GM bias voltage)

How to quickly test an oxygen sensor circuit (GM bias voltage)


I got a 1994 Lumina that I wanted to show how to do an O to signal integrity test using this o to signal bias voltage symptoms or emission failure fixed o to signal and before we put a sensor in it I want to show how to quickly isolate a wiring problem between the computer and the sensor and we’re going to use this bias voltage on the scan tool to do to do that for us all right I’m doing a wiring integrity check to make sure that the o2 harness is good from the computer all the way out we’re gonna use this bias voltage right here on the scan data 454 millivolts and what I’m gonna do is I’ve already unplug vo2 and I have the connector where we can see it and what I’m gonna do is I’m gonna take my test light and I’m just going to touch the tip my test lights connected to ground and I’m gonna touch the tip of the o2 harness connector sorry the harness side connector I’m gonna touch it what that’s gonna do with the test light connected to ground is of course the test lights not gonna light just using that as a jumper and if you look at the scan tool I’m now reading for millivolts take my test light off of that connector it jumps back to 450 that tells me my harness is good from computer all the way out to the sensor and we need to put a sensor in this

28 Replies to “How to quickly test an oxygen sensor circuit (GM bias voltage)”

  1. Hi Paul
    Could you please upload a Video of how to test a wide band O2? I know that we can only look at scan data on Toyota ,but is there anyway to scope them?

    Thank you Nice video

  2. I was looking at a vauxhall vectra the otherday and it had a fixed 450mv on the o2 wire (black)and no voltage on the ground wire (grey) sensor plugged in I didnt think to bridge them together to check the ground but I did touch battery + with my hand and o2 signal wire at the o2 sensor and pcm showed a change could I of had a bad ground with no voltage on it? the signal wire also had an odd 5volt pulse on it every now and then not sure what that was any ideas?

  3. No voltage on the sensor ground was normal. It should be 100mv or less on this design. Also the 450mv you had on the signal told you that the PCM and wiring integrity was good. There was really no need to do the PCM response test you did on a system that uses a bias voltage. I'm not sure what the 5 volt pulse was though. I have never seen anything like that on an O2 signal wire. Who makes the Vauxhall Vectra?

  4. vauxhall opel make the vectra. my o2 sensor voltage did not change with propane or an air leak just stuck at 450mv I am going to go back and short the black and grey to see if i get 0volts like your book says

  5. Ok thanks. Keep in mind if you do that test that the engine may need to be running for the O2 Scan data PID to update. I learned that the hard way on some of these bypass type tests. IF the scan data stays at 450 then you have a wiring problem. If it drops to zero then you most likely had a bad O2 sensor to begin with.

  6. Very difficult topic to cover hear. In short it is a small voltage that the computer sends down the O2 signal wire and is used for diagnostic purposes. (open/short circuit identification and heater circuit function).
    Watch my "2003 Jeep Liberty O2 Bias Voltage Testing" video with the 5v bias that Chrysler uses. It may help. Also watch my "94 Honda Civic O2 Sensor Signal Circuit Integrity Testing". I think this one will help too.

  7. It is different. I see you just bought my book! You will find the answers you are looking for in there. I'll be in touch.

  8. Quick question would this apply on a OBDI. I did exactly the same you did in your video but my voltage does not go to Zero when right at the PCM and still no change.
    No a 100% sure is a bad PCM

  9. yes, this will work with early models too. but there are variables to this type of testing. another 1 would be there may need to be in rpm signal before the computer will update scan data. a second 1 would be a bad computer ground would cause the same thing.

  10. I've got an Australian holden 2005 vz alloytec 190. Pretty sure same engine used in the U.S CTS cadillac. Computer shows im burning lots of fuel. I hook up a tech 2 to see the operation of o2 sensors. I have bank 1 sensor 1 saying 1.01:1. Bank 1 sensor 2 saying 416mv flactuating a little but staying in the 400 zone. Bank two shows exactly the same thing for sensor 1 and 2. Shouldn't sensors be flactuating ferequently even when car is on idle? Thanks for the helpful videos. The best

  11. watch?v=PsClEr03fPw

    I pulled that video from a tech 2 that shows the operation of the sensors i hope it could be help. Thanks in advance

  12. Every time I try to save this clip for later reference , I get this message ,You have shared too many videos recently. Please try again later. am I the only one who gets this message ???

  13. Hey man. Me and another tech were having a debate at work today about what causes an o2 to read rich. Now i was stumped for a minute but came to the conclusion that with extra fuel or less air there's a more complete mixture which leaves a smaller amount of unburnt oxygen. Is that the correct answer or am i just coming up with wild theories here? Also debating on leaks before the MAF and whether or not it would be seen as a load condition. Would love your input.

  14. To test wiring integrity cant you just unplug the sensor andsee if the fault code appears saying o2 circuit high

  15. I tried this test on 2 separate obd 1 vehicles. an 89' Lesabre and a 92 Riviera -One had a working 02 sensor and circuit, the other did not. (unplugged sensor , key on)both had bias voltage according to my scan data of about 453-454 mv. I wasn't able to see a change in either one when shorting the signal to ground as you did. the mv. remained the same

  16. Update, after trying the test again on both vehicles while cranking I saw a reaction on the car with the known good circuit. (MV dropped to about 22) The other car showed no change. Must have a wiring or computer issue. Thanks for the video!

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