zebra1550

My T100 has 151K miles and popped a check engine light last night. I had the code read and it's the front O2 sensor. Obviously I'm going to replace the front sensor, but should I replace the rear sensor at the same time? I realize it's not broke, but with 151K miles on it, it can't be that far behind the front. Any thoughts?

MTL_4runner

I would just do the front one only.
Mine popped a code for the front at 80k mi but now I am at 130k and still no code for the rear yet. The front one is really the only one that goes bad because the other is buffered by the converter. You may want to eventually replace it at like 300k mi but that is up to you.

blink

I agree with MTL... unless you have the urge to spend another 100 dollars. Id wait for the second one to throw a code

li_runner

This actually happened to me @ 128,000 miles. I did change both I figured it was time and at least it would not happen again anytime soon.

I thought it was fishy as well that both would go out at the same time.

zebra1550

Actually...the O2 sensors are $160 each. I originally bought a Bosch sensor from Advanced Auto. I couldn't believe it, but Advanced Auto was more expensive than the stealership. Advanced Auto $189, dealership $160, AA ended up price matching. Anyway, I got the sensor home and found the wire harness to be about 10" too short. Advanced auto lists the same sensor for the front and rear. Only the dealership lists two different sensors with two different length harnesses. Bottom line, I've got a front sensor on order from the dealer. It was really tempting not to install the bosch sensor on the rear. I just hate to eat $160 extra bucks if i don't need too.

blink

The first 02 sensor is the more important one of the two. If that one is out, then your truck would be running in open loop fuel mode vs closed looped, thus using the maps on your ecu. the downfall of this is that the ecu maps tend to run the engine rich, which cause loss of gas mileage, loss of performance, and also could prematurely kill the cats with the extra unburnt fuel. The second 02 is used just to indicate if your cat is doing its job or not.

If you were to ask if you should replace the first one cause the second one threw a code. i would suggest it. but since in your situation, it is the other way around, i still stand by my opinion of waiting for the second one to throw a code that its broken, before replacing it.

Hope I was able to shed a little insight on the matter to help you make a decision

MTL_4runner

Remember also on 99+ trucks the sensor is an air/fuel ratio sensor, not to be confused with a regular O2 sensor.
Make sure you get the right one for it to work correctly.

blink

MTL i thought about the same thing and realized he was talking about his 95 t100

MTL_4runner

Oops....hehehhe
Worth mentioning anyway.

zebra1550

Thanks to all for the help, I'm going to replace the front O2 sensor for now and wait on the rear.

blink

sweet....tell us how it works out

4RUNR

So it is not a simple thermometer?

Gadget

If you find that you need a new O2 sensor check out www.URDUSA.com. We have the best kickass prices on real DENSO direct plug in O2 sensors like the ones that came stock.

Gadget

Phisherman

My front one went out 2 weeks ago. I had it fixed the next day for an obscene amount. The very next day my rear one went out. I had Andy knock some sense into me and I bought one that night from URDUSA.com.

If I were you though, I wouldn't order one until it goes out. No need in buying something you might not ever need.

MoveOvr

Hi MTL,

I'm from Ontario, i was told by my mechanic at the toyota dealership that our 4runners (here in canada) are different from the models in the US. he tells me that my 2000 runner still has the O2 sensors, and didnt switch to the air/fuel ratio sensors till the 2002 models. do you know if this is correct?...i was told by 2 mechanics at 2 different dealerships...are you able to shed any light on this?

Thanks
Bill

MTL_4runner

That would be news to me.....best thing is just to verify by part numbers....that will tell you for sure.
Mine is a US vehicle so I haven't really checked that.

If you find this to be true, please do post back.

MoveOvr

ya, the good people at urdusa are looking into it for me. i'm a technical retard, and dont know where to start looking. i'm just going by what my mechanics told me.

aside note: i'm coming to montreal mid december....any good party places??

Gadget

The easist way for the home mechanic to tell for sure if he has a front Air/Fuel Ratio sensor or an O2 sensor is to see if the rear O2 sensor will plug into the front plug. If it will plug in you have and O2. If it does not, you have an Air/Fuel Ratio sensor.

The plugs are different so you can't plug the wrong one in.

Don't try to run the vehicle like that, just to a plug in test and see. Then you will know what to order or not.

Gadget

MTL_4runner

Gadget,

Isn't the bung tapped with different threads as well on the A/F sensor?
I thought I remember someone tapping out one at one point to make an O2 sensor fit.
Mine is a 96 so I have yet to see the different setup.

Gadget

The two different type of sensors look exactly the same and will fit the same flange type bungs. Only the plug is slightly different, but you have to stick it in the other plug to know it does not fit properly.

Gadget