Does an oxygen sensor have to be sealed to work correctly? Mine has been put into a replacement piece of pipe without the mounting socket. Does it have to be sealed to function? The computer says it is bad. It was put in by a mechanic by punching a hole and two mounting screw holes to install it. It is loose.
Toyota, Previa 1993
The correct way is to weld a bung to the pipe and screw the sensor into it. It has to be sealed to function. You did not have a mechanic install this. You may think he was a mechanic, he may have represented himself as a mechanic, but he was no mechanic.
Yes, it must be sealed.
Any seepage will let in outside air (and its oxygen) and throw off the reading.
It will also make exhaust noise and release exhaust fumes under the car, which could find their way into the passenger compartment.
Thank you. I am beginning to believe that.
He told me the sensor was bad according to the computer and needed to be replaced ($120 part). He disconnected it to help the car run better until I got a new one to install. It actually fell off leading me to think it was not sealed.
You are confusing me now. Why wasn’t the sensor mounted in its original bung? Was the pipe replaced?
I explained in the original post, a replacement piece of pipe. No bung.
Thats what I thought but your second post confused me. So you had this mechanic replace the pipe and he did not weld on a bung. Then you got a check engine light and he says the sensor is bad and he disconnected it. Then the sensor fell out. Is that right?
If it fell very far, it may be damaged now, can’t tell. But the first step is to have a bung welded onto the pipe and the old sensor installed properly. Then if you get a check engine light gain and you get a code for the sensor, then yes it is bad. I’m not sure that OBD I systems monitor the oxygen sensor, it is usually checked with a voltmeter while the engine is running.
It was hanging over wire strap and had not fallen off.
Thank you for your help.
I think I am in the market for another mechanic.
Good idea, good luck. If you have an independent muffler shop in your area, they should be able to fix this.
Drilling a hole in a piece of pipe and just hanging an O2 sensor in there? No mounting bung to thread it into or flat mounting flange to bolt it down? That’s got to be one of the most hacked up things I’ve heard of lately.
Agree with asemaster time for a new guy,
If that guy will mangle up an O2 in this manner then one has to wonder what else he’s done in the past; and maybe currently… 
You need a new guy. If the bung hole is missing, it’s the wrong pipe. Doing what he did and pretending it’s okay is not the correct solution, trying to cover by saying it’s bad and disconnecting it is either lack of basic knowledge or downright pathetic “don’t care” repair work.
As mentioned above, yes, it has to be an air tight seal. Otherwise O2 coming from the outside air (instead of the engine exhaust, which is where the computer thinks the sensor is reading) will make the computer think ever-more gasoline needs to be injected to burn off all that extra O2. And you’ll end up with a rich mixture and not-so-good gas mileage. Edit: And likely a check engine light.
That said, it is not entirely impossible to jury-rig an O2 sensor that wouldn’t leak. But doing so would probably take so much time to rid all the air leaks that it would be better just to do it correctly, using a piece of exhaust pipe that has the correct adapter welded on it.
hahahahah mountain finally said it!
I knew if I kept up with this thread my juvenile sense of humor would be satisfied…
The guy that did this is a hack, pure and simple.
It isn’t at all uncommon to get a wrong pipe from a supplier. A simple slip of the little finger, a misread part number (it that fly poop on my eyeglasses?), or even an engine variation or a mid year design change (that’s why dealers use VIN numbers now) is all it takes. Intelligent bipeds with fully functional brains and any modicum of integrity simply get it replaced with the right pipe. This guy… well, what more can I say.
Yeah, the money you wasted so far on this guy ,you coulda had it done right the first time.