How do you test an O2 sensor?

digger · Post by **digger** » 06 Jun 2007, 13:02

How do you test an O2 sensor to determine if it needs to be replaced? I assume you check voltage. If so, across which wires and under what conditions? What is pass/fail? Thanks.

greasefingerss · Post by **greasefingerss** » 06 Jun 2007, 17:08

The downstream O2 sensor has no affect on the air-to-fuel ratio. It is used by the ecu to determine if the Cat is spent/bad. It does this comparing the both O2 sensor values. The upstream one is always high in oxygen content. So if the downstream one does not report a lower oxygen content, then the Cat is not converting the available oxygen to other substances. Like CO + O2 yields CO2.

For narrow band sensors, the oxygen sensor generates a voltage signal which is proportional to oxygen content (signal wire is the black one and the gray wire is ground). The signal is a sinewave so using a voltmeter to diagnose will only tell you if the sensor works but not how well it works. It will oscillate from 0.2 to 0.8 volts. The average valve should be close to 0.5 (but only for the front O2 sensor) A sensor yielding a constant average valve above 0.5 is considered a Rich condition. A scanner or oscilloscope are the best tools for this.

digger · Post by **digger** » 06 Jun 2007, 18:39

Thanks for the info. I'll give it a try.

I've got a '94 850 turbo that I bought a few months ago and when I bought it the CEL was on and I got numerous error codes. I found some vacuum leaks which I fixed and cleared the codes and CEL light and the CEL has not been on since. However, I just checked the codes and got 435 and 443. The car runs pretty good but the gas mileage is not great(about 16MPG city) and it has some slight surges on acceleration.

I hate to replace the O2 sensors unless I have a pretty good idea that they are bad.

greasefingerss · Post by **greasefingerss** » 06 Jun 2007, 19:02

16 mph is not good at all. Assuming that it is tuned-up, I would clean the MAF with electrical contact cleaner and recheck the mileage. Then if that does not help I would chuck in a new upstream O2 sensor.

digger · Post by **digger** » 07 Jun 2007, 12:12

Thanks again for the input. I've looked at all the posts on cleaning the MAF and have been tempted but have never been sure if my car needed it. Might go ahead and give it a try. I'll check O2 sensor too. I'll report on how it turns out. Might be a few days.

sergoparia · Post by **sergoparia** » 15 Jun 2007, 14:52

Hi guys,
I got the same problem, I am more familiar with metric system and my car takes 16-18 liters/100km. It is

. The code was 0133 so I checked all accessible connections, cleaned the throttle body, changed the plugs, air and fuel filter, last thing I did was the upstream oxygen sensor.
It does not changed much.
The lambda-zond light is still on and I am getting really pissed off about that.
I have read in about cleaning the MAF. Could you please tell me where can I find more information about this procedure.
Is it really helpful???

Thank's.

CarVolvo · Post by **CarVolvo** » 15 Jun 2007, 20:04

Testing O2 sensors on the workbench.

Use a high impedence DC voltmeter as above. Clamp the sensor in
a vice, or use a plier or vice-grip to hold it. Clamp your
negative voltmeter lead to the case, and the positive to the
output wire. Use a propane torch set to high and the inner blue
flame tip to heat the fluted or perforated area of the sensor.
You should see a DC voltage of at least 0.6 within 20 seconds.
If not, most likely cause is open circuit internally or lead
fouling. If OK so far, remove from flame. You should see a
drop to under 0.1 volt within 4 seconds. If not likely silicone
fouled. If still OK, heat for two full minutes and watch for
drops in voltage. Sometimes, the internal connections will open
up under heat. This is the same a loose wire and is a failure.
If the sensor is OK at this point, and will switch from high to
low quickly as you move the flame, the sensor is good. Bear in
mind that good or bad is relative, with port fuel injection
needing faster information than carbureted systems.

ANY O2 sensor that will generate 0.9 volts or more when heated,
show 0.1 volts or less within one second of flame removal, AND
pass the two minute heat test is good regardless of age. When
replacing a sensor, don't miss the opportunity to use the test
above on the replacement. This will calibrate your evaluation
skills and save you money in the future. There is almost always
*no* benefit in replacing an oxygen sensor that will pass the
test in the first line of this paragraph.

http://www.wps.com/LPG/o2sensor.html
--
Rick Kirchhof Austin, Texas | Experience is what you
Domain: rick AT posms.cactus.org |

digger · Post by **digger** » 02 Jul 2007, 08:49

Update - The wheels of progress turn kind of slow sometimes in my household.

I tried cleaning the MAF and that did not help. So, I installed a new universal front oxygen sensor and so far the O2 codes and catalytic converter codes have not reappeared and the surging is gone. Plus, the car is running better, even though it wasn't too bad before. Don't know if it improved the gas milage yet. Will update on that later.

As for the O2 sensor test, I chose not to test it installed. But, rather did the bench test. I just connected the black and gray leads to the multimeter. It reached 0.6V in 20 seconds and dropped below 0.1V in less than 4 seconds, no problem. During the 2 minute test, it got up to 0.9 V but then slowly and steadily dropped to around 0.6V. So, I guess it failed this test.

I didn't have the nerve to do the bench test on the new sensor cause I didn't want to take a chance on damaging it. Although it probably would not have hurt it.

If anybody cares to know, I'll update if I see an improvement in gas mileage.

Thanks to all who helped. This is a great forum.

Volvert · Post by **Volvert** » 20 Oct 2007, 14:30

I have problem with oxygen sensor. I get OBDII error code P0032 HO2S Heater Circuit High Voltage Bank 1 Sensor 1

Originally when I got the error code, I discovered my old sensor had insulation cut from all 4 wires and they were effectively shorted. I fixed the wires and the code was gone for few weeks, but then it returned and then I got replacement sensors from Ebay. Unfortunately replacing the sensor did not fix my problem.

Comparing the new sensor and the old by multimeter did show the old has the heating circuit open. So it is likely bad.
Measuring heating circuit resistance of the good original downstream sensor shows 7 Ohms, the replacement sensor shows 4 Ohms. I hope this is not causing the problem.

I did measure the voltage coming to the heating circuit on the connector to both sensors while sensors disconnected and engine key on.
The upstream shows only 8V the downstream shows 12V. Both get direct 12V from a fuse, but the ground is not direct, I suspect it goes through some circuit, maybe in the computer to detect the status of the circuit.

Would you have some suggestions what else to check or should I finally give up and drive to dealer?

My Volvo S60 Engine is: B5244S

Robert

1998v70xcbill · Post by **1998v70xcbill** » 02 Jun 2015, 12:37

This is a great old post. I'm have o2 sensor problems. My code is P0130, I have an obd11 laptop program, so i can see the o2 signals on both o2 sensors. Both seem to work some times, but will drop out. My mileage is 14-15 city (bad). I think, I have a loose connection or bad ground? My good pre o2 sensor was ripped out by the wires, from a piss off mechanic. I took the car back to the mechanic because they put the wiper arms on the wrong side. I could not open the hood without hitting the wiper arm. They just replaced my evaporator and drier for $1200 parts and labor. They fixed the arms, but.

Long story short, I had a old o2 sensor i installed to replace the pre o2 sensor. I't's history (current o2) is a cheap ebay replacment ($30). I installed it (a long time ago, to fix my p0133 AT THE TIME) It did not fix the problem, IT WAS AN EXHAUST LEAK). This was when i just just my car 89v70xc and had many codes. Well I clogged both o2 sensors when i aggressively seafoamed the engine to find the exhuast leak. The leak was at turbo the manifold (2 of 4 nut missing). I pulled both sensors, cleaned both, installed cleaned post sensor, but install the orignal O2 sensor that came with car. I assumed it was good, because replacing it with ebay sensor had no effect at the time. (and it was very easy to remove, thinking it was fairly new).

Just to clarify, The o2 sensor (installed now) is a low mileage ebay $30 special.

Anyway, I'll first check the wiring, And if a pull the o2, I do the torch test. I am tempted to buy a another cheap ebay sensor, or should i check tasco?

I know this is a old post. Please suggest other posts for O2 testing.

Bill