Upstream o2 sensor replacement

I know that this thread is like 10 years old. But I also happen to know that at least @WHCSC is still active on this board, but so are others I've seen on upstream O2 sensor replacement threads. They pretty much all die without any answer (other than a mechanic did it, "got it done," or - LOL - this one with no responses.

But some of you have done this, I'd think!

I currently have my wiper cowl off. Did the plugs and working on O2 sensor. I got what I thought would be the hard part which is breaking the old sensor free. Got it moving and then went to work on disconnect of the plug. Holy crap. That's that hard part. It took me a while to even find the damned thing. Wth would they put it there?

Anyone have any tips/advice on just getting the damned thing unplugged? It's just a simple little one-barb catch, and I can get my skinny little arm up in there to reach the plug, but then all I've got to work with is like 3 fingers as there's no room for anything else. I tried jamming all sorts of things up into the female side of the plug to release the barb but to no avail.

I will post a basic "how to" here when I'm done. Unfortunately, I didn't set out to document the whole thing for a walk-through with pics, but I'll get something together.

 

Maybe try spraying the plug/socket with some good quality penetrating oil and hope some gets in between to loosen up whatever dirt and grime has found its way between the two. Could you get a phone/camera in there to get a clear view of the plug, just to confirm how it goes together and what locking mechanism it uses?

Other than that I have not got anything else.

 

TLDR: I managed… If you remove the wiper assy/tray (easy if mildly tedious), it’s a little tight but there is good access to the sensor. You’ll want an O2 sensor removal tool. While I did get mine with a crow’s foot style, you’re way better off with a socket-style (but this goes for virtually any O2 sensor removal. You can probably get a loaner set from a big-box AP store that has both). The HARD part is getting the damned thing unplugged b/c the plug is crammed up into a niche about 8-10” down under the inverter coolant reservoir (and fuel and A/C lines). You might find a smarter way, but I jammed my arm down over the valve cover and around the corner and was able to get finger tips to the plug. (It’s very tight and I am bruised at the elbow). The difficulty is getting the plug retainer released – a release tab (harness/female side) that clicks onto a barb (sensor/male side). You just can’t work it with three fingers! You’ll need to get something jammed up in there that will release the tab. I ended up fashioning something of a “tool” out of a piece of electrical wire and got that to work (pic way down below), but this is also something someone smarter than I could probably do better.

Fuller version:
Well, what an adventure. But it's done. I think the smartest way to do it is to take it to a shop ;-)

I’m sure there are probably smarter ways than what I did but here it is:

1) Remove the whole wiper assembly and tray. (It’s easy, if mildly tedious:
- remove wiper arms (14mm nuts – leave yourself alignment marks on arm and spindle to make replacement easier);
- remove 2 phillips head screws from the black plastic cowling (at extreme outside corners up by windshield);
- remove the rubber trim pc at the bottom. (Annoying plastic barbed retainers – mine are already for sh** but work them from the bottom with needlenose or something to be “nice” to them).
- The plastic trim is 2 pcs. Just pick up at the front, slide them down a little and they come right out. (Clips on the underside go up under the edge of the windshield, so don’t ham fist it – just a gentle slide down toward the front of the car so the clips clear. Side note: unless you’ve removed this before, assume that you will find a wet, muddy swamp underneath and plan time for cleaning).
- Once that plastic is off it’s all just staring you in the face. 5 10mm bolts hold the motor assembly on, and then 7 10mm hold the metal tray (2 at each end / 3 down the middle).
- At any point during this, remove the small relay box (2 10mm) and associated wiring harness running along the tray. You just get the harness out of the retainers on the wiper tray and it all easily swings to the side. The plug for the wiper motor has to be poked through too – just goes through a grommet that is easily popped out.)

2) With the wiper stuff out of the way, there’s reasonably good access to the O2 sensor.

- You WILL want to have an O2 sensor removal tool. You won’t get a wrench on it (if anyone was thinking about that. Alternate to O2 socket is to cut the wire off and put a deep 7/8” socket on there, but I shy away from such things just in case I “fail” and have to drive it to a shop). I used one of the crow’s foot variety just because it’s what I had around. You’ll be much better off with the socket version. Some big box parts stores have them in their loaner tools. I was regretting not thinking about that and having one.
- There is not a lot of room to work side to side / swing room for a ratchet, but it's enough. The overhead clearance is actually quite good. I was able to get my reasonably bulky 1/2" ratchet down there. It broke free pretty easily (tho’ that was after I went from the 3/8” to 1/2" ratchet – longer handle and I have a 1/2 to 3/8 adapter).
- If it doesn’t break free, all I can say is the usual stuff – caution, patience, penetrating oil, heat, and stuff.

3) The fun part! The sensor plug is waaaay down under the inverter coolant reservoir, fuel line, and A/C line, and just crammed into a tiny little space (circled in red - lousy pic).



I’ve spent little time under this hood so maybe here’s where I might have been smarter, but it just didn’t look like there was any straightforward “move X out of the way” or whatever. At first I just didn’t think I could get it at all, but I found “a” route to get an arm and hand to it – and you’ll need reasonably thin arms/hands or I don’t think you’d get it. I went in between the large wiring harness on the back of the valve cover and the A/C line at the fire wall, then around to the right and around the corner.



- There’s a heater hose on the way and you probably have to go between the hose and the the engine (I had to) rather than around the hose on the firewall side. (Getting your arm in there is super-tight – my elbows are a little “knobby” and are now bruised up from jamming through there. And I have some nice chafing on my wrist/lower forearm.)
- Once crammed in there I was able to get fingers to the plug, but it’s getting it un-locked that is hell. The plug wasn’t stuck. It’s just one of those tabbed retainers – a barb on the O2 / male side, and notched tab on the harness/female side. Look at the wiper plug - same principle. You press the back of the release on the harness side to lift the other end and clear the barb. But there is no accessing the tab to depress it and release the barb. (I fiddled with seeing I could get the tab from the top but nothing I had was nearly long enough. But there’s still almost no room to work, and those tabs suck anyway. They like to bend or break more than just release). I started with trying to get in there with things like picks and screwdrivers to get the tab to lift it/slide under it – but you’re working with like 3 fingers and have almost no real control. No matter what I tried, it inevitably jumped up over the release tab (and fell out anytime I thought I *might* have gotten it).
- I eventually made a simple tool out of a short piece of solid copper electrical wire (14awg, but 10 or 12 would have been better). I stripped about an inch at the end, pounded that flat with a hammer, and then put a little crook at the end hoping I could get it to ride down under the tab rather than hopping over it.



- It was not easy – basically poke and pull and poke and pull and so on – but I finally got it. This whole episode was hours, but once I figured that out I was out of the woods in like 15 mins or so. So there’s a “tip/trick” that makes it more do-able (except for whatever I should have done smarter).
- Side notes:

- the harness side of the plug is clipped into a retaining bracket and that is your friend. If nothing was there to hold that harness side then I’d likely say “fugettaboudit.” So, you know, don’t ham fist it so much that you might break that clip.
- Also, the sensor wire is held to an A/C line with a black plastic ring. I fiddled with that for a minute but it wouldn’t yield, so I just cut the old sensor wire and pulled it all out (tho’ heck you could just leave it behind). The wire likely doesn’t need to be “retained” at all but I very loosely (like not even snug) zip tied it to the heater hose as that was pretty easy to reach. It will keep it from flopping around.
​

4) To finish up …do everything in reverse!
- Plugging the sensor back in is pretty easy b/c you just need to click it back in rather than un-locking it. Just make sure it goes all the way – the retaining tab should click when it fully seats. (Barb on sensor side of the plug faces toward the driver’s side).
- When you get back up to the plastic trim up at the windshield, put on the passenger’s side first. There’s a tab on it that goes under the d. side.
- Putting the wiper blades back on is a PITA b/c the hood is in the way no matter what. Partly prop it up a little (I stuffed a roll of disposable shop towels up under the hood) while you get the things aligned and the bolts snug enough to get the blades back down. Then pop the hood and finish tightening the bolts.

It was a total PITA, but I could now do another pretty quickly and somewhat easily. But I still might opt to just have a shop do it! ;-)