3FE code 21 issue

[Yota truck nut]

So I have had a pesky code 21 since I have had this 80. code 21 is main o2 sensor issue or circuit issue. I have replaced the o2 sensor with a denso OEM sensor. I pull the efi fuse under the dash for 30 seconds and start the truck. within 5 seconds the CEL is back on. So if it is a new sensor and I cleared the codes, where do I start to look?? what am I looking for?? the wiring harness leading up to the o2 sensor is free of bad spots, burn marks, dirt etc... where does the wiring harness go to after that? any help is appreciated

 

[Mixelplix]

It seems that you're referring to one O2 sensor, when there are actually two on a US 3fe FJ80.

If your exhaust is stock (which it might not be due to the 'downpipe' being prone to rust) you should have two exhaust pipes which exit the exhaust manifold, and hug the inner wheel well - they will then have two o2 sensors (one in each pipe) under your drivers door upstream of the catalytic converters.

Based on your description, you're getting code 21 due to there being only one o2 sensor.

Want to post some pictures? They will be helpful in this situation.

There are two wiring pigtails for O2 Sensors (this will help you determine which one is missing). One is toward the centerline of the truck, and comes out from above the transmission, the other is on the outboard side of the truck, and hugs the area where the inner fender meets the underside of the truck.

The centerline o2 sensor services cylinder banks 4,5 &6. The outboard o2 sensor services cylinders 1,2, & 3.

 

[Yota truck nut]

thank you so much!!! there is a plug in the kick panel exactly where you said it was. I never thought to look for another plug because the Haynes manual said there are FJ 80s with one or 2 o2 sensors, and the exhaust pipe showed no signs of there ever being an o2 sensor bung. thank you very much for your help. I will now be going to get that fixed.

 

[western flyer]

Those pesky Haynes manuals. We need to get this man a FSM.

 

[CJF]

thank you so much!!! there is a plug in the kick panel exactly where you said it was.

Huh?

The plugs aren't inside the cabin.

If you're planning on working on this rig yourself, you *really* need to get the Factory Repair Manual asap.

Meanwhile, it would be interesting for all of us if you could get us some pic's of your exhaust set-up, especially what's going on reight around the area under the driver's seat.

 

[Yota truck nut]

I said kick panel but I meant inner fender well.. Anyway, I got a new o2 sensor and took it to the exhaust shop and had them drill and weld a new bung into the pipe. The denso sensor was 57 bucks and the exhaust shop cost me 40 bucks. So for less than 100 bucks, the CEL is now off and the truck is running great. Thanks for the help. SO now, anybody got a link for a FSM???