Another O2 question: 87 Syncro, 94 EJ22, GoWesty Cat

[T3TRIS]

Hello,

I have another question about oxygen sensors for which I wasn't able to find an answer yet.

We have a 1987 Syncro with a rebuilt EJ22. The shop wasn't great for sharing details and all I can say is that we think the engine is 94. I am not sure how to identify if it's an OBD1 or OBD2, or even SOHC or DOHC (and I barely know what that means).

The van runs but it has had the O2 sensor light on ever since we bought it a year ago. The previous owner said he couldn't get it to turn off. My research shows that this light is triggered by mileage and not necessarily by an O2 signal. <- This was confirmed below. It's 60,000 mile trigger. There is a box by the front driver side wheel through which the speedometer cable goes through. The box has a button visible from the front. Pressing the button with the key turned on (but engine off) resets the O2 sensor light. Thanks Mavy_Flyer

When we got the van back from the shop, they had put the exhaust system back like it was, with an O2 sensor on the elbow before the cat and another O2 sensor on the cat, pre-cat side.

I bought a GoWesty cat and not knowing any better, installed it in the same orientation as the original one. I also bought two new O2 sensors, one universal, one with a specific plug. Our wiring is a bit of a mess (which I know can be the source of plenty of issues, a custom harness is on the list for future purchases). The O2 sensor on the cat was wired to a legit two-prong plug, with the third wire was dangling (see photo). The sensor on the elbow was spliced to three wires, one of them being coaxial. When I took it apart, I found that the coaxial part was separated and just taped up so it wouldn't touch anything.

Caption: Wiring connected to the oxygen sensor on the cat (pre-cat right now). Left green female plug comes from the harness, right male plug and extra wire comes from the O2 sensor. I can't find where to connect the third wire. Obviously the two plugs don't fit quite right, they fit but can be installed in two different orientation. I assume I have the wrong O2 sensor. I also read that some older O2 sensors weren't heated and might only use 2 wires. Could this be the case?

Here are my questions:

1. Are O2 sensors basically the same, with only the plug and maybe threads differing?

2. If both O2 sensors are pre-cat, aren't they measuring the same thing? Wouldn't that tell the computer that our cat isn't doing anything? (I'm pretty sure this is a "yes yes" answer).

3. Would swapping the GoWesty around to have the O2 sensor post-cat be a good idea? (GoWesty confirmed that it could be reversed).

4. If I do indeed need two O2 sensors, which one, including the wiring, goes pre-cat and which one goes post-cat?

Thanks for any guidance!

Additional info after tinkering:
The O2 sensor connected to the wiring NOT shown in the photo (the spliced wiring with coaxial cable) heats up when the ignition key is turned on. The other O2 sensor has not heated up in my tests. I have swiviled that two-prong plug around with no luck.
I hooked up a multimeter to a random bolt on the frame. Touching the body of BOTH O2 sensors read 0.00 Ohms (though it'd make sense since they are on the same exhaust).

[Navy_Flyer]

Get under the drivers side front wheel and check where the speedometer cable attaches to a mechanical junction box about the size of a deck of playing cards. Just follow the cable up from the front wheel, and the cable will be attached to it, with another cable running from it up to the speedometer. There is a reset button on that box. Have the key on, engine not running. Press the button (you may need a pencil or screwdriver as the button is recessed). You should feel a click - but the box has to be energized (key on). That should turn off the dash light. The light is only a reminder after every 60,000 miles to change your O2 sensor, nothing more. It counts revolutions - after 60,000 miles it triggers that idiot light on the dash. it is not connected to the O2 sensor in any way.
Some of us eliminate that junction box and run a continuous speedo cable from the wheel to the speedometer. Those are available from the usual sources.
_________________
1987 Westfalia, Automatic. EJ25 VANARU Conversion

[T3TRIS]

Oh my goodness, that totally worked! It's the simplest of my problems but heck, it's been such a mental puzzle to get this thing working right that as simple dash light turning off feels amazing!

Thanks for the info

Now, I'm going to flip that cat around.

[Navy_Flyer]

[T3TRIS]

Update:

I turned the cat around in order to have an O2 sensor upstream and another downstream. I haven't driven the van yet but everything looks and sounds good. It fires right up as it used to. The upstream sensor (spliced in) heats up, the downstream sensor (connected to the mis-matching plug) doesn't heat up. I read the the downstream sensor isn't as critical as the upstream one.

I'm unsure which one is supposed to be in the front or back. If things don't work really well, I can switch the plug around (it shouldn't be possible right, but what I have fits both ways) and even swap the sensors.

I'll give it a test drive tonight before a 1,000 mile road trip this weekend. Wish us luck! We're driving our van down to Tijuana to get the rust repaint, new paint and reupholstered.

[T3TRIS]

Alrighty, I'm revisiting this old topic now that I know a whole lot more about O2 sensors, OBD1 vs OBD2 and electrical wiring!

Since our engine and transmission are out (I just recently reinstalled the gas tank), I figured I'd do some wiring harness cleanup. It's a mess in there, full of gooey electrical tape, wires that go nowhere, unidentified connectors and melted harness sleeves.

While in there, I figured I'd try to identify exactly what that plug pictured in the very first photo was for. It has no power going through it that would heat up the oxygen sensor, what is it? Pulled up the Bentley, searched for the wire colors (blue with a green line and brown) and sizes and eventually figured it was most likely the plug for our coolant level sensor!

Our sensor alarm had never worked (we bought the van a couple years back). I tried finding the issue a few times but couldn't figure it out. Last summer, we had our coolant system checked by a mobile mechanic and found out that, while our coolant system seemed solid, our coolant level sensor was completely shot (I wondered where that prong had gone...):

We purchased a new sensor last July, popped it back in and, lo and behold... nothing changed! Still no alarm.

So if that first plug was our coolant level sensor wiring, what was actually connected to our coolant level sensor?! The plug itself is the same, fits perfectly and that's what has been plugged into the sensor ever since we bought the van. Here's a photo of our engine bay recently after purchase of the van.

After more Bentley search, I figured that what was plugged into our coolant level sensor was actually the crankcase vent heating wiring (black and brown wires), which reminded me of the coolant sensor failure last year! I ran back to our coolant tank to take the less-than-a-year-old sensor out and this is what I found:

I guess we've been cooking our coolant level sensors (and coolant?!) with the power meant to heat up the crankcase vent heating element!! The plugs are the same though the wires are different. Given that that's how our system was wired from the beginning and the engine itself is running strong, thinking that our crankcase heating element and coolant sensor wiring were swapped wasn't my first guess! We don't even have a crankcase vent!!!

Our engine and transmission (and battery) are still out so I can't see if the system works now, but dang, what a mix up! That mystery wire wasn't an O2 sensor after all...