Civic HX - CVT to Manual Transmission Swap

Friday, January 4, 2008

11. ECU, oxygen sensor and wiring

This write up is only intended as an overview of converting your CVT Civic to Manual transmission. By reading further, you are agreeing that by attempting to do anything you see here, I am in no way responsible to any damage you cause to your transmission, your car, or yourself. I suggest you purchase a service manual for all the details, such as torque specs & tightening order.

There are are 2 ECU's 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 ecu's from automatic civic's 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 ECU's 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. There's 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 you'll 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....

You'll need some soldering supplies for the harness.

You'll 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 that's 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 I'll live with that for now. Maybe this summer when I have my EG to drive, I'll 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:

Here's a list of pinouts that will come in handy when hooking up the wideband wires to your ECU's harness: Thanks to 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 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, I'm driving the car with the CEL #70 on.


Blogger esco562 said...

did you ever get your car running right? Im in the process of doing this swap now, i dont know wether to continue with the y5 head or just swap the head for a y8 head along with the mani and tb.

January 17, 2008 2:10 PM  
Blogger Brian said...

nope, still the same.

yeah looking back I would have done the same, but i wanted to keep the vtec-e for better gas mileage.
if you go with a different head, you'll need
- a different ECU (obviously)
- probably a different dizzy (hx models have a different dizzy part # than other models) but try the hx one first
- y8 intake manifold (hx one has egr valve in it) if you get a new IM, might as well get it from a manual along with the throttle body.
- might want to pick up the engine harness and the ecu harness as well. The hx's ecu harness is wired into the separate ecu that controls the CVT tranny. then you could rip that all out instead of hacking the stock harness and testing with a multimeter forever.

January 17, 2008 7:29 PM  
Blogger esco562 said...

So your main problem right now is the rough idle (because u need the 5 speed Intake many and throttle body) and the cel because your using the cvt ecu right?

So if you got the 5 speed intake mani and thottle body, all you would need to do is switch over to the 5 speed ecu and your good to go.. right?

My CVT ecu is being chipped to run 5 speed so im hoping when i get the EX intake mani and ecu everything will be ok.

January 18, 2008 8:54 AM  
Blogger Brian said...

When I had the 5-wire o2 and manual ECU it ran rough, bad enough to make me decide to switch back to the 4 wire o2 and auto/cvt ecu and live with the CEL #70.

"So if you got the 5 speed intake mani and thottle body, all you would need to do is switch over to the 5 speed ecu and your good to go.. right?"

I would think so, but no way to tell unless I do it for sure.

"My CVT ecu is being chipped to run 5 speed so im hoping when i get the EX intake mani and ecu everything will be ok."

I don't think you can chip an OBD2 ecu. I am not going to use my manual P2N ecu now, if you want to buy it.
If you get the EX intake manifold, you'll need to get an ecu other then the P2N or P2M because it won't have the EGR valve. So with a little wire hacking, you would be pretty much converting your hx to an ex if you put a y8 head on.

January 18, 2008 11:46 AM  
Blogger Matt said...

I just finished this same swap. Your guide was very helpful. Greatly appreciated.

I have however managed to get it all to work with the Manual Ecu and 5 wire O2. I bought the L1h1 Ntk #24300 sensor off ebay for $170, got the manual 97 hx civic ecu for a $100 here locally and hardwired the sensor according to your pictures/diagrams.
I had a code for the iac and the 2nd o2 sensor, My car didnt have a cat or a 2nd sensor at all.

I ended up hardwiring the 2nd sensor to right at the ecu as well.
I got a ford mustang IAC and just made an adapter plate to bolt the new Iac to the existing Hx intake manifold and throttle body. Installed a Cat as well...

Car runs great, no codes so far.
about 80 miles into it. Going to get it Emisions tested and inspected on monday.

Make sure you have the correct sensor, Alot of people on ebay are selling the l2h2 sensor claiming it will work as replacement for the l1h1 sensor. IN most cases it seems to work as it is just the newer updated sensor. But, for the hondas you have got to have the correct older, more exspensive sensor

June 21, 2008 11:09 PM  
Blogger Victor said...

Hi Brian,

First off good work on the guide. I plan to do a swap myself. I'm using D15Z7 motor with CVT Questions though:

1. If you retain the auto ecu, does it mean the IACV fix and the primary O2 does not need to be performed?
2. The Honda manual stated that the car will not rev pass 5k rpms with no VTEC if shifter position is in P or N. To enable normal engine functions i.e. VTEC shifter position must at D; but car will not start in D. I was thinking to trick the auto ECU by jumping P & D together. How did you get around this?
3. Where did you hook up the reverse light switch?

January 20, 2009 6:10 PM  

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