Still trying to find the front O2 sensor on my 99 runner. I've gotten some feedback that says it's supposed to be in front of the cat, but that's where my air/fuel ratio sensor is! I can't see anything else in the general area of the cat that looks like the sensor. I did, however find one a little further back (towards the muffler) that has a line running forward (towards the cat) could that be the one, or is that my rear 02 sensor? Please help!:pat:

 

Yes you have a sensor in front of the cat. It is either a standard O2 sensor or a air/fuel ratio sensor. You will only have one or the other infront of the cat and not both.

What kind of project are you working on.

Gadget

www.GadgetOnline.com

 

Ok, a few weeks ago my check engine light came on. I took it to the shop and they said the computer code was a front oxygen sensor. I called Todd at Toyota of Richardson, ordered the sensor - he looked the vin # up - sent it out. I put the sensor in last weekend - had to modify it because the grooves didn't line up with the slots in the "bung". Then I was informed on the forum that it was because that bung was for the fuel ratio sensor and that there was also a front o2 sensor somewhere. When I looked for it this morning, the only thing I could find was the one I described as being further back. Now what? Could the O2 sensor code really mean the fuel ratio sensor?

 

Yes, the O2 Sensor code actually means the A/F Ratio sensor. You will either have the A/F Sensor if your truck is a CA Emissions model, OR the O2 Sensor if your vehicle is a Federal Emissions model for that year, but not both.

After the 2000 model year, all 3rd Generation 4Runners came with the front A/F Ratio sensor.

Hope this helps.
Dr. Z

 

I've got a 99 4 runner. Todd looked up the VIN and sent the O2 sensor - not the fuel ratio sensor. How could this be if the VIN said o2 sensor? Ok, so I should order the fuel ratio sensor to take care of it, right? Can I put the O2 sensor he sent in the rear then?

 

The rear maybe a different part number.

Gadget

www.GadgetOnline.com

 

You might as well replace the rear sensor with the one you modified as long as it was not damaged in the process. Check the numbers with the dealer to be sure that the sensors are the same behind the cat. Sorry to hear about your ordeal with the A/F sensor vesus the O2 sensor, but hey, we all make mistakes. I have certainly done my share of screwing things up as well.