JohnRaven

Okay, so I've been thinking my o2 sensor was going/is bad. So I decided to test it before I bought a new one. I took it off and hooked up a ohm meter to it and it read 5.9...

Is that within spec? Here is where I connected the meter...Notice the Black and Red..... :p



Am I good to go??? Does it need replacing?

JohnRaven

bueller?

runethechamp

Just look it up in the FSM. It will take you less than 5 minutes.

js9924

that is not the correct way to check the o2 sensor. you need to check the sensor when the car is running. the o2 puts out a very small millivolt reading check it by starting up the vehicle, then either pressing your probes through the shielding or by pressing pins into the wires and attaching your leads to the pins, you should be able to watch the millivolt reading fluctuate until it warms up then remain fairly constant you can check the heater when it is unplugged however. you do that by putting you ohmmeter probes at B+ and HT- which should be the two pins opposite the retaining clip on the harness. if you have trouble look at the FSM links in the sticky for pics. good luck

It looks like you are testing the heater and that is within spec

JohnRaven

That is what I was looking for. THANK YOU!

Don't worry, I'll be back!

js9924

happy to help I am just returning the favor for many who have helped me

dcg9381

Good post, JS.

JohnRaven

Alright, so when I tested the o2 sensor when it was off the vehicle I touched my ohm meter to the 2 black terminals/wires.

Now to test the actual sensor, I connect my meter to the blue and white wires, correct? What should the milivolt reading be once it remains somewhat constant?


I just tested it... I clipped the + (red) to the white wire. and the - (black) to the blue wire.

After I had them connected, I watched the meter BEFORE starting the truck. it started at about -1mv and went up to 30mv and kept going... Once I started the truck, it was at about +70 MV then went down to about 65mv, then jumped back and fourth between 63mv and 65mv for a little bit, then slowly kept dropping...

What does this all mean? Am I doing this right??? Agghhhh! I'm so confused!

JohnRaven

I'm starting to feel like that little annoying kid who asks questions all the time...

gte718p

how about testing a one wire o2 sensor?

js9924

As long as it was hooked up right, which I think it is, I think it is fine according to my manual (haynes) between 100-900 millivolts is the operating range for the o2 sensor in closed loop mode. what are your symptoms why did you think it was bad?

gte718p how is it possible to only have 1 wire?

JohnRaven

Alright, so I must not have been getting a good enough connection to the wires. I fixed that...so now I KNOW I had it connected right and I'm pulling about .450 volts. So.... 1/2 a volt.... Is that within spec? (while the engine is running btw)

The reason why I think my o2 was/is bad is because I'm getting terrible gas mileage, and it looks pretty old, so I just thought it might be bad. I tried pulling the codes, but there were none to pull. So I wanted to make sure it was either good or bad before I spend $100 on a new one.

My 'rig'

1992 4Runner 3.0 automatic
31x10.5 BF Goodrich AT Tires
Cleaned throttle body
Sea foamed the gas tank, twice.
Tires properly inflated

New K&N Air filter
New NGK plugs and wires
Tires balanced, front wheel bearings repacked, and front end realigned.
greased about 6 Zerk fittings on the drive train, still need to get at a few more.

machabees

You can get an O2 for cheaper than that. look around on here. others have purchased them for less than 50 on ebay and such.

JohnRaven

Okay, so I finally found the 'testing procedure' of the o2 sensor... WTF? That is a bunch of micky mouse crap. That doesn't make any sense at all.... I guess I'll just buy a new o2 sensor and see if that fixes my really bad gas mileage....

js9924

if the readings are correct (sounds like they are) it is fine and that is not your problem more than likely.

What are your symptoms? besides poor mileage
Any engine codes?

cutboggers

1 wire sensor = old carb junk, heard it was a "DUMMY" sensor

scope103

The O2 sensor, when warmed up and running, should fluctuate back and forth between about 0.25 volts and 0.85 volts about 8 times in 10 seconds. (you may need to run the truck at about 2500 rpm to keep the sensor temperature high enough, but mine will fluctuate correctly at idle). If it is just sitting at 0.45 volts, most likely the sensor is dead.

To diagnose your O2 sensor you go to .... under the truck? No! You go to the diagnosis box attached to the fuse box. There is a connector labeled Ox1 which goes right to the sensor. You'll need a voltmeter with one of the lcd bars that imitates a needle (you're looking for up/down 8 times in 10 seconds; too fast to watch digits). Start it up, give it 30 seconds to warm up, then hold it at 2500 rpm (thereabouts). Look for up/down 0.25 to 0.85.

If it reads zero or 13.1 you've got a connection problem. If it sits at 0.45 I'd suspect a dead sensor. What about sitting at 0.25 or 0.85v? Then the O2 sensor is probably working, but you're running too rich (mileage problems) or too lean (knocking?). To track that down you need to lean out the mixture (create an air leak) or enrich it (propane?) That may be the "micky mouse" you're talking about.

Do you have a connector labelled Ox2? Welcome to California! That's the second O2 sensor downstream of the catalytic convertor. If that one switching back and forth at the same rate as your upstream sensor, your cat's dead.

Toyota recommends replacing the o2sensor at 80,000 miles. But you can buy 4 good voltmeters for the price of an O2 sensor. Do the test.

dcg9381

That's right.
The critical parts are having the truck fully warmed up and running it at RPM (not idle) to see it dither. Personally, I like to test it at the ECU with it plugged into the computer, just probe the back of the connector.

There's no "fixed value" test for the 02 sensor - it's meant to be dyamic.


Testing it at idle won't work - these trucks idle rich from the factory.

malorty

I'm having a similar issue. My CEL is on and throwing code 21. I checked the O2 sensor heater and it is at 5.9ohms (whithin spec). I checked the voltage with the truck running at 2500rpm at the Ox1 slot in the diagnostic box but unfortunately I only have a digital volt meter (no lcd bars). It does appear to be fluctuating however from the numbers I could get (up and down from about .3 to .7 volts) Is this not accurate enough to tell if the sensor is bad? Or if it does seem right what else could it be with the code 21?

Few things to mention-

I have a rusted hole in my muffler that leaks exhaust but it's been like that for a while without the CEL coming on.

My gas mileage is bout 16mpg

Sometimes i get some studdering at freeway speeds

There is a Ox2 slot in my diagnostic box but I don't see a second downstream sensor nor a spot for one and the slot doesn't register any voltmeter readings.

Thanks all for any help!!

*91 pickup V6 4wd extended cab*

scope103

What does code 21 mean? http://personal.utulsa.edu/~nathan-b...85diagnosi.pdf

You started in the right place with the ohmmeter, but just because the open isn't in the sensor itself doesn't mean you've got power to the sensor. Start by inspecting the wire at the sensor; it's a tough environment. Check for 12v on the wire-side of the same connector at which you checked for resistance sensor-side (That power comes from the ECU, and there is no published test procedure, but I'm guessing the engine needs to be running for there to be power to the heater.)