How can you check it to see if the oxygen sensor is bad or if suspect.....just replace it and don't waste the time. Comments

Mike

First it depends on how many wires you sensor has. If there is only one, it's easy. That's the signal wire. If there are 2, it's signal and ground. The one wire sensor grounds through it's case. Three wires are two heater wires and a signal. Four wire are 2 heater, one signal, one ground. Our C3s are one wire sensors. The only Federal emission C3s with sensors are 1981 and 1982 model years.

Turn on the key, unplug the sensor, and test the wires. The one with 5 volts is the siganl. Plug the sensor back in and start and warm up the engine. Fully warmed, monitor the voltage on the signal wire. It should change between 0.0 and 1.0 volts. You won't see this full range. Now run the car very rich. You can do this by choking the carb, or adding propane or carb cleaner. It sensor should go to at least .8 or higher volts. After it is choked a bit, let it get full air. Now it should drop lean to .2 or less volts. If it does this it's good. If it only changes 3 or 4 tenths of a volt, its weak and needs replaced. No change, it completely failed.

Ken Styer

|UPDATED|2/12/2004 2:55:25 PM (AZT)|/UPDATED|

Okay here I go again.
The oxygen sensor is usually misunderstood. Many think it is an indication of rich or lean condition. In general, this is accurate. But it actually is not true. The oxygen sensor monitors the amount of oxygen in the exhaust system. It generates a signal on the results of sampling the exhaust on a continuing basis. If the voltage signal is .45 volts or higher, the computer considers this to be a rich signal, and drives the fuel system lean. If the voltage is less than .45 volts the computer considers this to be a lean signal and drives the fuel system rich. This back and forth cycle is known as "closed loop". If the oxygen sensor is not responding or the computer is not montoring it, the fuel system is in "open loop". There are some GM updates where they changed the switch point voltage from .45 to correct a specfic problem in driveability or emissions. (I know they don't count, but Fords and Chryslers use .5 volts instead of .45 as the switch point.)

The computer is fast and accurate, but stupid. There are many things that can cause additional oxygen to be in the exhaust system. An exhaust leak will not only allow exhaust out, but due to the pulse/vacuum effect (the same thing that makes headers work) it pulls air into the exhaust system as well. This "false" air adds oxygen to the system, causing the computer to drive the system rich. But it never sees it go rich due to the false O2. The result is the car runs excessively rich all of the time. Sometimes this will turn on the check engine light and set a code. Sometimes it won't, depending on driving conditions. Your fuel mileage goes down.
There are other false air supplies. A.I.R. pump systems leaking or not operating correctly. Vacuum leaks. Cannister purge. Improper engine timing, ignition problems, low compression, or carbon buildup causing a partial misfire or complete misfire will add O2 to the exhaust. If you didn't burn it all, it's still there.
EGR itself won't supply false air, but will cause a misfire causing false air. In short, anything that makes the car run wrong will affect the fuel mixture.

The sensor itself is one of two types. Zirconia or Titania (I may have spelled that last on wrong). Both operate in a similar fasion. All of our C3s use Zirconia sensors. They are like a battery. The Zirconia is the sensor element, coated with a thin metal on each side. One side is exposed to the exhaust. The other side has a small vent that exposes it to outside air. Each side acts a a plate in a battery. The Zirconia acts as the acid. When there is a lot of O2 in the exhaust there is very little chemical difference between the two plates of our battery, and very little voltage is produced. With little O2 in the exhaust we now have a chemical difference. Lots of O2 on one side, little on the other side. With differently charged plates, our battery produces voltage. It does have to be at or near 600 degrees F. to operate.
The titionia sensor (found in some C4s and C5s) operates in the exact same manner, except it does not produce voltage. It creates a varying ground. We have a 5 volt supply to the sensor and it pulls the voltage to ground. It still operates in a 1 to 1.0 volt range after it warms up.
Sensors with heaters warm up faster to get the car into closed loop faster, for better fuel control, better fuel mileage, and cleaner emissions.
And yes the Zirconia sensors also have a 5 volt reference that the car uses as a reference until the sensor warms up. How can it operate at less than 1 volt when it is supplied with 5 volts? Difference of Potential. The sensor is a much stronger current than the 5 volt. It's like hooking up a AAA battery to you car battery. The AAA will have whatever voltage the car battery does while they are connected (until it blows up). You can also think about throwing a cup of boiling water or an ice cube into Lake Erie. The lake temp won't change. That's the Difference of Potential.
Hope this helps.

Ken Styer

|UPDATED|2/12/2004 2:58:33 PM (AZT)|/UPDATED|

How can you check it to see if the oxygen sensor is bad or if suspect.....just replace it and don't waste the time.
Answer: All oxygen sensors are bad,, once you remove the cats, you don't need them anyway.

Sorry, I couldn't resist. Oxy sensors play a major role in the emissions adjustments of the computer. Sometimes, a strong fuel system cleaning will help clean them out. Most of the time, by the time you get irratic or non-existent readings, they should just be replaced. Try not to get the universal ones, they're cheaper but rarely are as accurate.

You still need an oxygen sensor of you do a TPI/LT1/LS1 etc conversion. And as far as the universal ones not being as accurate, I do not find that to be true. The universals do not have the factory end on them, they need to be soldered and shrink wrapped to the original connector, that allows them to cost less.

I sure didn't think $12.99 was too much to pay from Knects, not to have to fabricate another. That's on my '82 CE. The $60 was expensive for my 4 wire on my Ford Pickup.

|UPDATED|2/13/2004 6:27:09 AM (AZT)|/UPDATED|

Were can I get an O2 sensor for my '82?