There are are 2 ECUs for the HX. P2N (cvt) and P2M (manual).
The P2N uses a 4 wire primary o2 sensor. The P2M uses an expensive 5-wire wideband primary o2 sensor.
Other OBD2 ecus from automatic civics have an additional set of pins in the B section. Neither the P2N or P2M have any pins in the B section of the ecu pinout.
(the P2N & P2M ECUs are on top, the bottom ecu is from an automatic dx with the pins in the B plug section)
The CVT HX uses a separate ECU located behind the driver side kick panel. Theres a harness going to and from this CVT ECU.
I purchased the 5-wire o2 and the P2M ecu for the swap.
The first thing youll need to use the 5-wire o2 is an 8 pin harness to connect to it. I clipped this one from an old OBD1 harness I had laying around.
This Space Reserved! I had a piece of paper that I wrote all of the ECU pinouts on for 1-8 on this plug. It is essential info and I know I have it in the garage somewhere....
Youll need some soldering supplies for the harness.
Youll be adding onto the plug, a few feet should be long enough to reach the ECU.
Any connections you make should be crimped AND soldered.
Here is the wideband (cleaner one) compared to the old 4 wire o2 sensor.
Before you run all of the wires through the firewall, make sure you have everything right. Short cut through the passenger door for testing.
And thats where my idea of using the manual ECU and 5-wire o2 ended. After I did all that work, the car was running rough. The electrical system was already screwy from the wires in the junction harness that got pinched by the rear bracket bolt. So it could have had to do with that, or I also read that I needed to use an intake manifold & throttle body from a manual civic. Well, the HX manifold is the only D16 OBD2 one with an EGR valve. So in order to see if this was going to work, I had to find an intake manifold & throttle body from a manual civic hx. I needed to drive my car, so I scrapped the whole idea of using the 5-wire o2 & manual ECU. The one good thing when I had it hooked up & running was no CEL #70 for the transmission. But Ill live with that for now. Maybe this summer when I have my EG to drive, Ill be able to try looking for the manifold & throttle body from a manual HX. I am told that the reason for this is the manual cars use a 2 wire IACV, while the automatic ones use a 3 wire IACV. I am going to experiment and see if I can splice 2 of the wires from the 3 wire IACV together, since I believe one of them is used when driving and the other one is used when not moving. I think this may be the reason for the occasional bouncy idle when coming to a stop, or putting the car in neutral and coasting when using the automatic ECU. Besides the CEL being lit constantly, and the bouncing idle, the car runs great with the 4 wire harness & automatic ecu. I left the CVT ecu plugged in as well. When driving with it unplugged, I got another CEL, #30, instead of the #70 I got before.
Below is the information for wiring the wideband o2 sensor to the manual P2N ecu
Engine Harness connector for the 5-wire o2 sensor:
Wideband 5 wire & 4 wire O2 diagram:
Heres a list of pinouts that will come in handy when hooking up the wideband wires to your ECUs harness: Thanks to http://ff-squad.com for taking the time to post such useful info!
Here is some useful information about the 3 plug vs 2 plug IACV (Thanks again to http://ff-squad.com for taking the time to post such useful info):
This part of the swap will be revisited at a later date when I have the time (and it is warm out) Until then, Im driving the car with the CEL #70 on.
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