o2 sensor dangling under 4-runner

[koobs]

Hey all, was just walking back to my 4R in a parking lot and noticed something hanging under the chassis. Looked close and I think it is an o2 sensor. I can't tell where it is supposed to go in. Look like the part of it is supposed to have screws attach it to something?

 

[gamefreakgc]

Photo didn't work that you attached, but here's what our O2 sensors look like (at least most of them anyway):

There's one that plugs in on the exhaust pipe near your front axle, and a second one between the cat and the muffler. If you have a California emissions, the first one is tucked up higher before the first cat, almost in the engine bay at the bottom.

 

[koobs]

yeah, looks like it is. I edited the image, should work now. I think this one is the rear one?

 

[JayRolla]

Priceless.

 

[gamefreakgc]

Seeing your cat in the picture, yeah that would be the rear. I'm concerned on WHY it came out though. The exhaust pipe has studs on it that the O2 sensor slips into with nuts holding it on. No way it should fall off by itself.

 

[animator]

Another "no way that's falling out on its own" post.



There are two nuts that are generally very well-rusted on holding that thing, and those things don't generally loosen up on their own, and definitely not off of both studs entirely.



Speculation says someone was in the process of stealing the cat and got spooked. Or didn't have the right tools to finish the job. And if that's the case, that's awful nice of them to unbolt the 02 instead of simply cutting it, like they did on mine, causing me all sorts of fun rebuilding a wiring harness...

 

[jeremyc74]

Is the truck loud now? I'm betting a previous owner capped the hole and it's been tucked up in there until just now.

There's no way that just fell out. :suspicious:

 

[Salman]

by now your check engine light should be on...you need to get under your truck.. it is 2nd o2... Get the wire brush clean the rust area i.e. pipe and bolts....get new gasket and 2 nuts... put the o2 back on.

 

[koobs]

When I bought the 4r 3 years ago it had a hole in the muffler, so it ran loud then. Had the muffler swapped out a few months after so it sounded much quieter, but maybe it was still louder than normal and I just didn't notice.

If I had to guess I would say that it might be a little louder now than before, but she runs and idles rough already so hard to tell. I was already taking it in on Tuesday to see why it runs rough (CEL is pointing to a fuel injector or maybe compression problem- hopefully the former!) so I will just have them put it back in I guess.

 

[JayRolla]

by now your check engine light should be on...you need to get under your truck.. it is 2nd o2... Get the wire brush clean the rust area i.e. pipe and bolts....get new gasket and 2 nuts... put the o2 back on.

It could easily not throw a code if its plugged in.

 

[gamefreakgc]

It's not a fuel injector, the O2 sensors control fuel flow. Which is wildly swinging around under your truck at the moment! Plug it back in, secure it down and all will be well again.

 

[koobs]

It's not a fuel injector, the O2 sensors control fuel flow. Which is wildly swinging around under your truck at the moment! Plug it back in, secure it down and all will be well again.

But the code is throwing p301, p304. Aren't those different codes?

 

[gamefreakgc]

Oh, well maybe you might be right. I'd still clear the codes and get that O2 sensor secured. See if they come back again.

301 is misfire in cylinder 1, 304 is misfire in cylinder 4. If anything, it's your coil pack that's gone bad. 1 and 4 are connected by the same spark plug wire so if the coil pack went bad on #1, the slave coil on #4 would not work either. Maybe start with new spark plug wires since it's a maintenance item and much cheaper. NGK and DENSO are best (and cheap on rockauto.com)!

 

[calimobber]

Post like this make me just :doh::doh:

get on your back and look at the exhaust pipe right where that o2 sensor is hanging. There will either be a hole in the exhaust or a hole that has been plugged with something like others say may have happened.

No idea how it came about, but if you can and there is a hole get 2 bolts and put that o2 sensor back where it belongs

 

[Arnezie]

These were my rusty nuts :lmao:

 

[calimobber]

These were my rusty nuts :lmao:

ouch maybe its more common than I think!

 

[Benski]

ouch maybe its more common than I think!

On a long trip I noticed my engine sound getting deeper and louder. I just figured a hole rusted through somewhere in the exhaust pipe. I stopped in a store, and walking back to my truck I noticed my O2 sensor hanging down. Looking under the truck I saw nothing but rust left on the studs. So those of you who say the nuts don't just rust away, they do!

 

[TheDurk]

On a long trip I noticed my engine sound getting deeper and louder. I just figured a hole rusted through somewhere in the exhaust pipe. I stopped in a store, and walking back to my truck I noticed my O2 sensor hanging down. Looking under the truck I saw nothing but rust left on the studs. So those of you who say the nuts don't just rust away, they do!

229K in Delaware, on the beach? I bet they do. It's also possible you are on your second sensor and non-stainless nuts were used at that time. In general, though, the OEM nuts outlast the sensor, if not by much.