Car question: How do I access the oxygen sensor through this tiny hole?

I’m trying to replace the front O2 sensor on my 2001 Mazda Protege, but it’s located inside a small hole that I can’t get a wrench through…

Picture 1 shows the extent of the setup.

Picture 2 shows the size of the opening with my finger for scale.

Picture 3 shows a close-up of the bolt-like hex part that I’m trying to get to.

Is there some sort of special automotive wrench or ratchet that’ll let me get in there? Or do I have to remove that whole whitish-gray assembly over the sensor (maybe the “heat shield”?)

Just trying to do it myself before taking it to the mechanic… any advice is appreciated :slight_smile:

You can try an offset wrench:

I have a couple in larger sizes that I use for O2 sensors. If that doesn’t work, you can remove the heat shield.

You need an O2 sensor socket like this:

Should be available at most any auto parts store.

Naturally, there’s a special tool for these.
It’s basically a socket with a slot cut in the side to allow the wire to pass through.
Like so.

That’s exactly it! Thanks, zwede and beowulff!

And steronz, how would you get an offset wrench through the wiring?

Go to any of the major auto parts stores (O’Rielly, Advance, etc.). They will loan you an O2 socket, for which you pay in full, but for which they cheerfully refund you in full when you bring it back. This is not a customer scam; it is the tool loan they advertise. They do it to sell O2 sensors.

Neat! Too bad we don’t have any auto chains in this small town. I could drive to the next town but it’d probably cost more in gas than just buying one. Good to know for the future, though :slight_smile: I wonder what else they loan…

Unplug it and feed the plug through the wrench. YMMV, but that’s always worked for me.

Lots of stuff. OBD2 scanners, brake piston retractor, gear puller, and more. Next time you’re there, ask them for a list of what they have available for loan; it’s a good list to have in mind the next time you need to do a repair.

It can work if the plastic connector is small enough to feed through the wrench opening. Turns out that’s a pretty big “if,” and my experience is that most oxygen sensor connectors are too big to allow this.

Have you tried a regular old box wrench? Maybe it’s a trick of the perspective, but it looks like you might be able to just barely get one on there and move it a fraction of a turn. You’re not dealing with a lot of torque with the o2 sensor (unless it’s rusted on) and so even if you can get the wrench partly on at an angle it may be enough. Or you may just round off a couple of corners.

I purchased a O2 socket today and managed to get the sensor out after a lot of shoving and cursing (it was on there TIGHT). The mechanic wanted $500 for the job, so doing it myself saved some $400. Thank you again, zwede and beowulff!

And if anyone was wondering wondering, a regular offset wrench wouldn’t have worked because 1) the nut part was about two inches deep in the hole and 2) the sensor came with a plug-type connector that wouldn’t have fit through the offset wrench hole. The O2 socket was definitely the right tool for the job.

It is possible, in a pinch, to modify an ordinary deep socket using a thin cutting disc in an angle grinder to remove sensors such as this (although sometimes the sensor is too long to allow this), I have a small collection of slit sockets and spanners bent to specific angles to do one job. The important thing is to ensure you have the correct size socket/spanner before you start hacking at it. A set of vernier calipers can be valuable here.

Good to hear it worked out. Nice feeling when you save hundreds!