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

This is an older GM vehicle (1994) but the tests I am showing can be applied to all oxygen sensor circuits that are using a bias voltage on the O2 signal wire. GM O2 Sensor Testing
Using O2 Sensor bias voltage to quickly test for an open in the signal circuit.
Symptoms:
- failed emission test
- check engine light
- poor gas mileage
Fix:
- replace faulty O2 sensor
Testing methods shown:
- how to use bias voltage on an O2 sensor to determine wiring integrity (opens and shorts)
Tools used:
- Scan tool
- incandescent test light
Related videos:
- Engine runs rich P0172, P0175 from a blown O2 heater fuse

Playlist:
- (Chapters 4 and 5) Fuel Trim and Oxygen Sensor Testing

On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!

Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.

[ScannerDanner]

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.

[joekuntzman]

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!

[nickayivor]

Good Afternoon ScannerDanner take care and have a great day ScannerDanner 👍 God bless
Great tutorial thank you 👍🌟🌟🌟🌟 🌟
From Nick Ayivor from London England UK 🇬🇧

[ScannerDanner]

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.

[ScannerDanner]

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.

[ScannerDanner]

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.

[UncleBerniesChannel]

As always, incredibly well done and informative.

[geojor]

thank you for sharing your knowledge...

[oileycat]

great videos just bought your book finding it really good !!! Thanks

[ScannerDanner]

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?

[SuperCarfix]

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

[oileycat]

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

[ateola]

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

[ولدزايد-ذغ]

Hi master
Air flow oxygen sensor has 2 blak wire showing 12 fix voltage when swich on and when engine on
So i think it should on off after some fix second
Is this pcm problem??

[nocturnando]

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

[nicholasaikens]

What if the o2 wasn't the problem? Would you have to get a new harness?

[soldiergudme]

Is the car turned on and not running or is the key out of the car ?

[jamesbarratt]

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

[oileycat]

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?

[brianwalck]

What terminal do you touch test light to 4 wire sensor. Tested voltage key on engine off. 450v touch test light voltage drops to 0 volts. Bad wiring or bad sensor I've tried many new and used good sensors still no luck. No vacuum or exhaust leaks found.2006 monte carlo average fuel mileage is 31 mph. no misfiring acceleration is 100% I'm baffled can't get catalytic converter monitor to set nearly 3000 miles.