I've scanned the Stickies and searched unsuccessfully for info on how to test whether oxygen sensors are still within spec. Is there a D.I.Y. test I can do? If I take it to the dealer is there a hi-tech test they can do? The easy thing for the commercial auto shop is to replace the sensors at my expense and then tell me the old ones were faulty. I am hoping there is some test that would definitely detect faulty 02 sensors.

There is no code on the ECU, but I wonder if failing oxygen sensors could account for the poor fuel economy I've been getting. As I understand it, failing sensors could be generating low voltage even in the presence of a balanced air/fuel mix. The low voltage signal from the O2 sensors would prompt the ECU to richen the mix unnecessarily.

 

Yeah. You dip it in water of a certain temperature and see what resistance the O2 gives. There are 3 temps and 3 resistance readings.

 

sure about the water part ?
its the thermostat that gets checked that way.....

Nick.

 

I'm curious about this too. I have two relatively new O2 sensors (less than 10k miles) and one that's got 40k+ on it. I worry that the rear sensor (the old one) is going bad on me b/c my gas mileage recently seems to be off. Of course, the only way to check that I know of is to wait for the code to come on! Not a great method!

Let me know what happens here...

 

Well you're supposed to check the O2 at 77*. If you heat the water to that temp and dip it into have an accurate reading. I could've sworn to god it was in the FSM but now I can't find it. ****, today is a very bad day. Anyway, at 77* the resistance between pins 1 and 3 should be between 2.3 and 4.3 ohms. The rear O2 should be between 5.2 and 8.2 at 77*. The water might cause rusting so turn off the AC in your house and wait for it to get to 77 and check the resistance.

 

Thanks to Dave Sz for info on testing front and rear O2 sensors. Sounds like this is not the day to ask, but if you do find the page reference in the FSM for these tests it would be great to know. That way I might be able to persuade my local Nissan dealer to make a copy of the relevant pages for me. If I succeed, I'll post what I learn.

 

I know there are tests for this in the haynes manual cause i just read about them this past weekend. You have to back probe them with a meter.

 

I just remembered that in scientific and engineering applications when you want to refer to "standard state" or "room temperature" for a chemical reaction or other experimental procedure you typically specify 25 degrees Celsius. That's just a conventional way of specifying "the normal temperature that human beings inhabit." The equivalent temperature in Fahrenheit is exactly 77 degrees. Probably the test for O2 sensors that specifies 77 degrees Fahrenheit only means "room temperature" as opposed to the extreme temperatures in the engine. I bet the test wouldn't yield detectably different values within any air temperature range that the person performing the test could tolerate.

 

The FSM said 77*(25*C). Of course you test the O2 when they are off the car nor when installed.

 

You can test its basic electronics to know that current is still running through it and what not, but I wasn't aware that a truly accurate test could reasonably be performed...

 

God!!! why do so much work, just back probe on the car with it running. It should cycle from high to low voltage, which in all reality cycle from lean to rich and back agin.