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G'day everyone.
I've got a question regarding GM o2 sensors. I've had a commodore with an LS1 engine in it that is constantly fouling the spark plugs causing misfires. I checked the car out and the B2 o2 sensor was stuck lean. I tried to force the system rich and B1 sensor responded (but was very slow to respond) B2 stayed lean. I removed to B2 sensor and it was absolutely covered in soot to the point that I was unable to clean the soot off and couldn't even see the holes in the sensor.
I made the call to replace the sensor and the customer (who is a good friend) made the call to replace both sensors. 2 new genuine sensors were installed and when I checked operation I now have no activity at all. Let them warm up, road tested to get the sensors hot, nothing. on both sides.
I pulled the sensors out and ohms tested the signal wires. Open circuit. We had another car in so we tried the o2 sensors out of that car and they came to life super quick and responded to driving them both rich and lean. I then Ohms tested the signal wires on the known good o2 sensors and I don't remember the Ohms reading off the top of my head but it was M ohms.
What I'm wondering is should the new o2 sensors be open circuit or should they have a certain resistance reading?
It's pretty normal for the O2 signal circuit to have very high resistance when the sensor isn't at operating temperature. Heating the sensor brings the resistance down. Some vehicles will actually measure/infer the O2 sensor resistance and display it on scan data. Over 30,000 ohms isn't unusual.
The open circuit in your replacement O2's might suggest defective parts? But, that doesn't explain why your O2 signals stuck lean after the first set. An open sensor would just make the bias voltage sit at 450mV. What brand were the first set of replacement sensors? Dealer or OE might be the answer.
If swapping out a sensor worked it really points to bad replacement sensors the market is flooded with junk and fake sensors.
You can do a rough and ready off car test on an O2 sensor using a multimeter and propane torch. wire Hold the sensor in a vice and with the multimeter connected across the signal heat the sensor and watch the voltage rise as you heat the sensor and then drop as you remove the flame.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Just want to add that an O2 signal circuit, when cold, will be an open circuit. Think about the 450mv bias (GM) that is being sent to the sensor. If there was any continuity through the signal circuit, it would pull this bias down immediately.
I originally thought bad new o2 sensors as I’ve been stung before with that using GM sensors.
My boss ordered 2 more and they were both exactly the same.
The car has 4.3v on one of the wires when unplugged and 1.9v on the other wire when unplugged. Both of them go straight to ground when plugged in.
Sorry for the late replies. I fly in and out to work and back so I haven’t been back to the car for a while. It’s a friends car that is just being done as I get time. I’ll get some more info on it when I’m back in Perth.
Hey everyone. Sorry for the stuff around with this post. The car had failed o2 sensors and the customer (who is a mate) ordered both sensors. I plugged in the new sensors. Both genuine GM sensors and they were both dead. I checked the heater circuit was working.
I ohms tested the new sensors and they were open circuit. I ohms tested another car(the same model) and it had continuity. Very high resistance (I can’t remember actual numbers now) but both sensors did have continuity.
We returned the o2 sensors to GM and they were swapped out for a second pair of o2 sensors. I checked the resistance of this sensor and it was also open circuit. After reading SDs comment about being open circuit until hot I realised that ohms tested new sensors is a waste of time.
So long story short we got 2 brand new sensors that were dead and then I started second guessing all of my testing theory.
Thanks guys.
Topic Author
But, that doesn't explain why your O2 signals stuck lean after the first set. An open sensor would just make the bias voltage sit at 450mV. What brand were the first set of replacement sensors? Dealer or OE might be the answer. 
