I searched for 8 hours trying to find a form with all the information needed. There’s one on here. But it’s vague.

when you swap a d16y8 into a DX and use the EX engine harness so you don’t have to wire in vtec you’ll run into “code 65”
this is because the computer is searching for the downstream o2 that obviously wasn’t on your d15 or non tec engine.
the body harness on your DX doesn’t have a connector under the car for your 2nd o2.

so to fix this you have two options.

1. Find a ex body harness and swap that into the car, this can save you from doing the wiring. But you may run into some issues with wires not being long enough in some parts. And also may take your whole day as you literally have to completely rip apart the whole inside of your car. This may lead you to breaking old plastic that is hard to find and definitely some clips.

2. you can direct wire the o2 sensor into your ecu. You’ll have to figure out how to read pinouts and just cut and solder some wires.
theres 3 wires you’ll mainly be looking for.

1. heater control wire. 2. o2 sensor ground wire.
3. O2 sensor signal wire.

the 4th wire you’ll have to figure out would be a constant 12V. Now you can find one on the harness that comes on with the key and shuts off when you turn off the car, or you can wire it to a switch with a fuse and relay. I recommend finding something on the harness near the ecu so you don’t have to have the wire in some odd location.

this is an absolute necessity if you don’t wanna or can’t find the correct body harness from a ex to put into your DX body.
Being 2023 it’s hard to find Honda parts. At least in my area.

you’ll need a downstream o2 sensor.
And down pipe that allows a downstream o2. Also
some wire. I used solder wrap heat shrinks.
The correct ecu. “P2P” is what I used.
And a couple hours and maybe some beer.

You’ll have to find an old o2 sensor connector for the old your wiring in. Or you’ll just have to splice the wires in.

So now for the o2 sensor pin out you’ll just have to look up what kind of o2 you’re using. Could be universal or a make specific one. There’s only 4 different kinds, your mostly looking for where the sensor signal and sensor ground wire goes.
The other two will be where your 12v constant and heater control goes. Basically the two complete a circuit and heat the o2.

I will add some pictures of the pin out. Good luck friends. Thanks to FF-squad for the pin out.

this will only work for OBD2a. OBD2B has completely different pins and colors.

 

How about removing the loom from the DX/LX engine harness and bringing the primary and secondary O2 sensor plugs around to the back and then re-taping the engine harness. Then, you can plug the primary O2 sensor directly into the engine harness. Next, you can purchase an extension harness adapter (or build a custom extension harness if you have the necessary plugs) to run under the car and then you can plug in the secondary O2 sensor.

This will be WAY easier than installing a replacement chassis harness and engine harness (and drilling a hole in the tunnel of the chassis).

 

becuase the DX. Only has the upstream sir.

 

The USDM DX chassis has two O2 sensors on the front of the engine... one at the top just above the cat and one lower down in or just below the cat. I have never seen just one sensor... do you have a Canadian or JDM chassis ?