Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Downstream O2 sensor replacement

Having some issues replacing the downstream o2 sensor. Upstream was a breeze to replace. I just bought this car used. Downstream seems to have had the female connector removed. Instead of the wires showing, it looks clamped off with a flat metal piece. Can it be rewired onto a new pigtail or do I need to go through the driver seat and replace the whole harness?

I can’t tell what your photo is trying to tell me. I will say, however, that the CEL won’t go off nor will it pass emissions inspection without replacing the sensor, or at least connection the one you have…

You should be able to buy a replacement female connector to repair the damaged one. They come with wire pigtails that are then connected to the cut-off portion. I like to solder-splice and shrink wrap the wires so no moisture will intrude. Some prefer solderless crimp connectors.

It’s capped off wiring where the female connector is supposed to be. There’s very little room to work, hopefully we can get it sealed into a connector without having to pull the engine out. I finally found the part online but even when I search the phrase not much comes up. Auto zone says they have a universal one but I have to buy the sensor itself with it so I’m not thrilled about that. I am however desperate to get the CEL off to pass smog so I’ll bite the bullet. The other sensor I bought I opened and it can’t be returned :roll_eyes:

This is what I was looking for. Much cheaper online of course. Was really hard to find. This was the only website I located it on.

Please tell us what model year and engine you have

1999 Toyota Solara V6

Here’s a quick video someone else made. All other videos talk about removing the driver seat. But that’s for the Camry I believe. Not the Camry solara. The o2 sensor doesn’t go through the firewall from what I can see. This is the first car I’m working on so I apologize if I’m not making much sense.

Here is the upstream I replaced. The part I circled is what’s missing from the downstream.

Your first picture looks like a ground connection, are you sure that is connected to the oxygen sensor wiring?

The downstream oxygen sensor wiring should pass though a grommet in the floor, the connector should be under the drivers seat.

I’m not finding anything going through the firing wall that’s related. The video I posted above, this is the same wiring hose. I’ll go out and try to get a video of my car

In the short clip I posted from YouTube, I’m pretty sure I’m fondling with the same wiring. It lines up above the valve end of the downstream. It’s not letting me upload my own video though.

This is for a 97 Camry. But the procedure is the same for your 99 Solara.


Since you are replacing the downstream sensor, doesn’t the new one come with it’s own connector? Or is the problem the corresponding connector on the wiring harness end has been removed for some reason, and is now missing? If that’s the case and a replacement harness connector is difficult to source, an auto electric shop could probably figure out a way to use a different connection method. They might decide is easier to remove the new sensor’s connector and just hard wire it to the harness by soldering, with no connector.

Yup, that’s the problem

Bad idea

Not only would it make replacing the sensor difficult, should it ever be needed in the future, an observant smog technician who sees this might fail the car

I circled the upstream, there’s another o2 sensor underneath leading up under the seat. Then there was a 3rd one with only the valve connected that I thought went to what appeared to be grounded wiring. The third valve location is down below the green arrow. I can barely reach it. We removed it and it is an o2 sensor but there’s no female connector to plug it in to

The wiring diagrams I’m seeing for the v6 3L 1mz-fe engine seem to show 3 o2 sensors. In one configuration (probably for Calif vehicles) they are all a/f sensors (a special type of o2 sensor). The 2 upstreams are located in the front area of the engine (one is near where you draw the red circle). The downstream location ( bank 1 sensor 2) is hard to tell from, the diagram, but is probably similar to the 4 cylinder engine, in the exhaust pipe after the cat, and the connector for it looks to be inside the passenger compartment & require the driver’s seat be removed or at least unbolted.

Note: Your terminology “valve” is confusing the issue. For o2 sensor circuits, there’s a “sensor”, and a “connector”. No valves, at least that I’m aware of.

Can you please share the link to the diagram? I pulled the downstream off today (the male/female connectors run up under the driver seat) and replaced it. The valve stem was by the catalytic converter.

After digging for more info, I have learned that the one I’m having issues with is bank 1 sensor 1. I found the valve location just not where the connector is supposed to go. This is the first car I have ever worked on so bare with me LoL!

Sorry, when I say valve I mean the part that screws in, not the male/female connectors.

The diagram I’m seeing shows both sensor 1 sensors are located towards the front of the engine compartment. Bank 1 sensor 1 is higher up on the engine than bank 2 sensor 1, and biased a little more towards the driver’s side. Do you know if you have a Calif configured car? For O2 sensor configuration, +B to HT should measure 11-16 ohms at room temperature. For A/F sensor, 0.8 to 1.4 ohm.

Sorry, unable to post any diagrams.

(upload://irAR1y9qqQQRx2pW8N0WRbLcbEG.jpeg) The image I posted above shows only bank 2 towards the front. It’s a v6 3.0 L

Everything I’ve seen on YouTube shows the plastic connector just above where I screw in the sensor. In the pics here you’ll see the sensor and then what I see above the sensor. The wiring isn’t even the right color but I see nothing else even remotely in this area. Going to have my husband jack it up again and I’ll get more pics from underneath.