Persistent CEL due to rear 02 sensor.

04, 4runner. 4.0 auto trans, 2WD, with about 175000 miles. I have had a CEL on this thing for IDK 5 years, maybe. It's the rear 02 sensor. I have replaced both sensors, twice. I reset the ECM, but the code just comes rite back within just a few miles. The exhaust, smells like it is running rich, just a little. Like it may be getting just a little to much fuel. The 4runner, runs fine, and is very dependable, but I would like to get the issue fixed, but I just cat seem to find any help on what else, may be the issue. The wiring for the 02 sensor looks fine. Nothing is pinched. Any help would be appreciated. I'm sure someone else has run into this issue.

 

Any sign of an exhaust leak anywhere? Also wondering if maybe your cat itself is bad. The cat in my third gen started failing around 160k and had very similar symptoms as you.

 

No, exhaust leaks. Bad, cats, IDK, maybe. I tried a trick, I did on my 97 Silverado. I made a set of 02 simulators with some of the honeycomb metal inside of the cats, after I gutted mine from my 97, Chevy. I have been running them on my 97, for about 8 years, with no issues, and no cats. It didn't work ony 4 runner though. Same result, after resetting the ECM, same code came back. P0420, I think. So, how much was it to replace the cats. I used to be a mechanic many years ago. I do all my own work, and as my name implies, I have been a certified welder, for years. Did you order a set of OE replacements, or did you get something else? Thanks for the reply.

 

Can a moderator please move this thread in the appropriate forum. Sorry, I didn't realize, I had posted it in the new member intro forum. Thanks, in advance.

 

I cut it out, cored it and welded it back In empty. I bought essentially a resistor and used that as a o2 sensor to keep the check engine light off. Before I got into law enforcement I was a welder fabricator for about 8 years. It's hard work but tons of fun. I've let my certs lapse but still like building and tinkering with things.

 

Thanks for the reply. I forgot about the resistor 02 simulators. I have seen them on line, but never in person. It is something worth looking into. I have been kind of looking for someone local, to tune the rear 02 sensors out of the ECM, but a lot of people just don't fool with Toyota's. As for welding, well, I have been welding for over 40 years. I do a lot of TIG work now. Mostly specially welding. Inconel, monel, SST, aluminum, stellite 6 hard surface, and yes, steel also. I am a gear head, and do a lot of car shows with my 97 OBS Chevy pickup. I enjoy doing custom automotive fabraction, and welding. As for work, LOL, well you know, work is work. There's nothing fun about work, but sometimes, something cool will come in the door. We see a lot of different things at the machine shop, where I work. We don't do automotive machine work though. Here are a few pics of my 97, OBS.

 

I've also heard of guys using a threaded insert as a spacer to move the 02 sensor out of the direct exhaust flow to change the readings a bit. I've never actually seen it work but have read a couple threads about it being effective.

 

Yeah, I tried that, and it didn't work. You may be in to something though with the resistor simulators. I could see that working. After all, it's just an electronic signal the the ECM, is looking for. LOL, I know just enough to get myself into trouble.

 

Stop blaming the O2 sensors.

They are trying to tell you that you have a combustion problem: running rich.

When you run for 5 years like that, you've probably toasted the CAT by now.

 

I agree, the 02 sensors are telling my, that I'm getting to much fuel. The question is, why, am I getting to much fuel? I have no other codes. Is there a common issue with the fuel delivery system, on the 4.0L engine that is know to dump to much fuel? Does the FP regulator fail in time, and cause this issue? Is the FP regulator located inside of the intake, like GM did, years ago? Or, is it on the outside of the intake? I was hoping that someone here has had a similar issue, and solved it, and could point me in the rite direction. If I have to cheat the rear 02 sensors to get the CEL to stay off, then that's what I will do, but, I would really like to fix the issue.

 

Long shot here because I have no experience with this code or issue, but does it smell a little rich because the cat isn’t doing its job and burning off the excess exhaust fumes? I’ve read quite a bit of threads about this code and most seem to say it’s due to a bad cat.

 

Yes, somewhat. That's why I think it's running rich. It's got that rotten, skunk, kind of fart smell, or burnt firecracker smell, but it's not real strong. It's not a clean exhaust smell, like it should be.

 

Also, this is the 4runner forum, I've been looking for. Active members, and everyone want to help. Glad to be here. Thanks guy's.