AdamP

I have a 93 4Runner with the 3.0 V6.

Having some issues in that it smells rich, is idling lumpy and the check engine light comes on intermittently. So I thought I would test the sensor in the exhaust just below the drivers seat. I believe that is the Air/Fuel sensor.

So I tested it cold and had a reading of 11 ohms. Took the car out for a 5 mile drive and then tested it again and only had a reading of 16 ohms. Other articles suggest it should read between 11-16 ohms at 20'c (about what it is today) and at 800'c around 23 ohms. Now I don't know how hot it gets after a 5 mile drive, but I would think that would be operating temperature. Whether it gets to 800'c at operating temp I don't know either.

Also, when I disconnect said sensor the check engine light doesn't come on and it makes no difference to the idle.

So, is my sensor unserviceable? And shouldn't the check engine light come on when it's disconnected.

Any help would be most appreciated.

Adam

kelvinb

800c is 1472f. that would be cherry red if it was indeed 1472f

AdamP

That's what this says
http://www.ncttora.com/fsm/2003/Repa...3/hos/insp.pdf

kelvinb

i understand. the leaner the mixture, the hotter it would be. so if its rich, it will not reach a high temperature. im not saying its not hitting 800c, but just keep that in mind when doing your tests.

AdamP

I assumed that that was normal operating temperature being as it's listed, but it is awfully hot.

Punchy

The O2 sensor does not detect heat it detects O2, Yes it is heated to bring the temp up and constant.

If you use an Ohm meter on it then it is toast now as the sensor side of it cannot handle that high a voltage.

Time for a new O2 sensor.

MudHippy

Wrong FSM. Try this one. In particular this section http://personal.utulsa.edu/~nathan-b...01heatedox.pdf

And yes, disconnecting it should definitely cause the CEL to come on as soon as the ECU goes into closed loop. As well as triggering a number of DTCs to be thrown buy the ECU(like 21, 25, and/or 26).

Hint: An O2 sensor ≠ A/F ratio sensor
http://www.autoshop101.com/forms/h37.pdf
Technically, it's more accurate to say that the O2 sensor detects the lack of oxygen, not its presence. Since the voltage signal strength is lower when more oxygen is being detected, and higher when less oxygen's being detected. So, in actuality, it should be called a No O2 sensor. Or perhaps a relatively little O2 sensor, since the voltage signal output is being generated relative/in comparison to the amount of O2 being detected by the sensor on the fresh air side.

That high a voltage? WTF do you mean by that? They don't even put out 1V. And ≤ 1V is certainly not considered "high voltage" by ANY standards(not to mention very closely approximating the actual operating voltage of the sensor).

AdamP

Well, I don't recall suggesting it measures or detects heat, but it would appear it gives a different reading depending on if it's hot or cold. Most likely down to thermal expansion of the materials involved no doubt.

Regardless
Mudhippy, a reading of 11 ohms cold and 23 ohms hot would indicate failure do you think?

I haven't measured the voltage feedback. Is it worthwhile or is the indicated resistance enough to confirm failure?

Thanks

Adam

Thanks for the links BTW.

4Crawler

iTrader: (3)

O2 sensor outputs voltage, not resistance. You measure at the check connector and should see approx. 8 - 0.2v to 0.8v swings in 10 seconds with the engine at operating temp and revving at 2500 or so. At least that is the 22RE testing spec. May need an analog volt meter or better yet, hook up an air/fuel meter in the cab and you can see what is up as you drive:
- http://www.4crawler.com/4x4/CheapTri...FuelRatioGauge

AdamP

The manual shows 2 tests: Resistance across +B & HT (listed first) and Output voltage. My question was: if it fails the resistance test, is it a total failure anyway and should I not even bother with the output test?

4Crawler

iTrader: (3)

Not sure what portion of the sensor is being tested with the resistance. Likely that is the heater coil part of the 4-wire sensor, if so if that is open circuit, that would imply the heater is burned out. I've never worked with a heated sensor as my '85 is a simple 1-wire sensor.

TheDurk

+B to HT is indeed the heater circuit. (HT= heater, those clever Asian engineers). So if you are out of spec, the sensor will not perform and needs to be changed--and if OBDII, you would get a constant CEL. I don't know what you get on OBDI as I haven't dealt with it.

AdamP

That's very useful to know. Thanks.

4Crawler

iTrader: (3)

All depends on how far out the heater resistance is. Basically that is a coil of wire that heats the sensor up to temperature. If the resistance is a little high, it may be that the sensor takes a little longer to come up to temperature, since more resistance = less current = less heat and ther other way around if the resistance is lower than spec. My take on readings like that or a relay coil, for example, is that when they fail, they are either a dead short (0 ohms) or an open circuit (infinite ohms), so if it is close to the factory spec, then it is probably OK. Different brand of sensor may have a heater coil that has more or less resistance than what the factory spec'ed.