Grunnen

So the p/o of my truck has no idea if the 02 sensors have been replaced. They look fairly new but i dont think that means much. Is there a way to tell if they are bad on an OBDI? I have no check engine light but i get terrible mpg's.

Yes I searched.

DupermanDave

there's a way you can test for resistance on the O2 sensor. There's instructions on the forums, and I believe I even saw some in a the FSM. But I don't know how to do it, I just know you can.

sb5walker

Resistance only tests the heater in the O2 sensor, not the sensor part. Look for resistance between 5.1 and 6.3 ohms (at room temp) on the two wires of the same color.

The sensor part has a couple characteristics that can be tested for, one fairly easily, the other not so much. The sensor, when heated, will generate a small voltage. In a lean condition, the voltage is below .45 V, rich will be over .45 V, but less than 1 volt. So if you had the ability to independently measure the percentage of oxygen in the exhaust, you could compare to the volts put out by the sensor. Not very many of us have such instruments lying around.

The other way of testing looks for a "lazy" sensor. Normally, the computer adjusts mixture several times a second, and therefore the O2 sensor if it is working right it will switch between over .45 V and under .45 volts at that rate. As deposits build up on the ceramic element, it takes longer for the sensor to detect a change in oxygen concentration, and so its switching rate slows down.

There is a procedure in the fsm for testing the switching rate. You attach the TE1 and E1 jumper in the check connector and then read volts between VF1 and E1. Volts will switch between 0 and 5 V. (VF is not a direct reading of the sensor but is generated by the computer in response to O2 sensor inputs.) On a hot engine, when maintaining 2500 rpm, there should be at least 6 "fluctuations" of the voltage in 10 seconds. Presumably that means a move from 0 to 5 volts counts as a "fluctuation" and from 5 back to 0 counts as another one, but maybe someone here knows differently.

http://personal.utulsa.edu/~nathan-b...42oxygense.pdf

Bosch sensors used on our trucks often fail this switching test because with the mounting position, the sensor element does not protrude into the exhaust stream far enough, and so its switching rate is slower than a Denso or NGK (NTK) sensor.

Another factor is that a poor electrical connection between the O2 sensor and the ecu could result in bad readings: with such small voltages, even a very small amount of corrosion will cause a rich reading on the sensor (over .45 volts) to be degraded to below .45 volts, which is interpreted by the ecu as a lean condition, so the computer would run the motor too rich, even though the sensor was working properly and generating the proper voltage.

Or a mechanical failure such as low fuel pressure or clogged injectors could cause a persistent lean condition, even though the computer was trying to inject more fuel. (In that situation, the ecu would probably throw a lean code 25)

Normally, a Denso sensor will last about 90k miles unless gunked up by something nasty. Allowing the engine to run rich will foul the sensor much more quickly.

I have only ever read of one cleaning technique for O2 sensors, and I think it has a low likelihood of success. Someone who had an old sensor and a lot of time on their hands might try it. It involves heating the sensor end almost red hot using a propane torch, then dunking the sensor in water with some isopropyl alcohol (maybe 10-25%), then heating red hot again and quenching again, maybe 3 or 4 times. This supposedly may cause the deposits to flake off the ceramic. I think it also stands a chance of cracking the ceramic, so I'd only try it on a sensor that had to be replaced anyway.

You could test whether this works by reading volts on the sensor when the tip of it is held fully within the flame where a rich condition would be expected. Look for more than .45 volts on the two uniquely-colored wires. After cleaning, look for the volts when sensor is held in same position for same amount of time.

Or you could just buy a new sensor.

DupermanDave

So then why bother testing an O2 sensor at all if you cant test its entire functionality?

JFCruiser

there really isnt a exact period of expiration for O2 sensors, my issue was the my mixture of gas and fuel was off which cause my car to back fire alot. The o2 sensors, basically sends signals to your cars computer telling it that either somethings wrong time to adjust or its all gravy.

So when ever you feel a loss of power or a decrease of MPG's it might be time to change your 02.

And if you were wondering where its located use this website, i cant really explain to you where it is so haha

http://toyotapartszone.com

rdharper

Just my opinion... and a few others, but the O2 sensor is probably the most-replaced-without-cause item in the last decade. They are simple, and reliable. They do not wear out. And they are difficult to destroy even if you try.

sb5walker

Well that's why most of us just replace 'em when they're over 90k miles old or we have a mixture issue with our engines that other work fails to solve.

But the switching test isn't a bad idea. The switching rate goes down as deposits build up on the sensor element. A good switching rate doesn't guarantee good readings from the sensor, but a bad switching rate does mean the sensor needs to be replaced.

Grunnen

thanks for all the advice. im going to test the switch rate tomorrow and probably end up buying new ones. the p/o has had it for 100k and has never replaced the o2 sensors so i think its safe to say i need new ones.

sb5walker

Denso direct fits will give best results. I get the part # from sparkplugs dot com and then search for "denso" and the part num on amazon - been real cheap there this year.

Let us know what you find on the switching test.

iamsuperbleeder

lol, I put a Bosch direct fit on my truck about a year and a half ago; the truck had 296500 miles on it and it had NEVER been replaced... and just after my rebuild, about 3 months later, the CEL came on and my gas mileage went to hell...

checked the CEL, code 21, O2 sensor heater malfunction...

bought a new Denso to put on it, and I'm keeping MORE THAN a quarter of a tank more a week! I drive 80 miles round trip to work and back every day, and I filled up Sunday... it's Thursday now, and I JUST dropped under a half a tank today

Kiroshu

I mean.... you can buy a new O2 from a parts for a 22r for 35-40 bucks. so yea. I think thought toyota calls for O2 replacement at about 90k-100k miles. If your truck is getting bad milage check your tire pressure make sure its even all round and above or at least 34psi. Hows ur driving? ur not going to get crap with 4-5k shifting. tune-up? Airfilter?

iamsuperbleeder

HA!

$35-$40 you think?

my Denso was over $100...

Kiroshu

^Thats a cheap bosch one i meant to say.

sb5walker

Code 21 is a "two-fer" - can be a bad heater circuit OR, could be that the sensor signal does not change for 60 seconds or more when speed under 60 and rpm above 1700 - in other words, ain't switching.

That is the code often seen with the Bosch sensors. There's nothing wrong with a Bosch sensor quality-wise - they just don't work in this particular application. Safer to buy Bosch for German cars, and stick with Denso or NGK for Japanese.

sb5walker

Actually the 87 and older 22REs used single wire sensors that are that cheap. No heater element, and worse, they grounded through the exhaust. Yikes.