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I also Posted in the General Forum not sure where is the best for this question as I can not find the answer in FAQ or other Forums

I recently swapped my D17A1 out of my 2005 Civic LX SE with a D17A2. I had the Motor, Trans, Wire harness and ECU from the donor 2003 EX. The motor is in and running on the stock LX ECU right now throwing the code for the 2nd O2 sensor, and no VTEC. I have an appt at Honda on Wednesday to have the ECU flashed to match my keys so I can get the VTEC working.

So in the mean time I have been searching all the forums for how to wire in the 2nd O2 sensor as the factory harness does not have it on it like on my LX. As I have read on all the forums the 2nd O2 sensor is part of the body harness. I dissected the harness from my old motor to get the wires for the O2 sensor. I have put the pins into the connector at the ECU where they were on the LX.
pin 25 wht/red Secondary O2
23 brn/yel Logic Ground
14 blk/wht SecondaryO2 sensor heater control
10 grn/yel Sensor ground

The last wire is Black/Yellow and I can't figure out where this wire goes. I think it would be pins 2 or 3 which are supposed to be yel/blk power source but not sure so I left it disconnected.

Checked for codes and now I have 8 with all these connected. It throws a code for both O2 sensors. When I take the Logic ground off it only throws the secondary O2 and heater code. So I tried the Logic ground on pin 24 which is also supposed to be logic ground with the same result, throwing 8 codes.

Am I having these issues because I am running on the LX ECU and did not flash the EX ECU yet?

The O2 sensors are new and for the EX motor not my LX O2 sensors, still using LX ECU at the moment.

I replaced the whole exhaust headers back with aftermarket, 1 O2 Sensor at bottom of header the other is about mid car under the console. No CAT installed, but 2nd O2 is with spacer.

Where do I wire in the 2nd O2 Sensor at the ECU?
There are 4 wires and a shield

Not that it matters but also replaced while the motor was out
Timing Belt, Water Pump, Thermostat, Crank Seal, Cam Seal, Valve Cover Gasket, Both Belts, Spark Plug Seals, Output Shaft Seals, Clutch Kit, Motor Mounts, O2 Sensors, Full Exhaust, Cold Air Intake, All Fluids

Please Help if you can, I am not your average everyday idiot. I am a Tech by trade and have worked on cars for years. I have owned this car since new and haven't ever had to do anything but the usual maintenance. Haven't done a swap since the early 90's. I also have all the tools and testing equipment at my disposal.
Thanks Again for all your help
Jason (n00b)
 

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Ok so here is an update since no one has offered any assistance.

I place the wires from the downstream O2 sensor into Connector E as they are supposed to go in the EX, still using my LX computer till Wednesday.

Now it is pulling 4 codes instead of the 8 hooked into the A connector

The codes are for both O2 Sensors and heaters

Is this because I am still running the LX computer with EX O2 sensors and EX motor?

I guess I will have to wait till I can flash the EX computer to work with my keys and then pull the code again.

Any help would be appreciated.

Thank You
 

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Black / Yellow is for ignition power. 4 wire O2 sensors have the following layout:

1 signal wire that sends 0-1 V to the ECU
1 ground wire for the above mentioned signal wire
1 ignition power wire for the heater
1 ECU switched ground for the heater

I'm not familiar with the exact layout of your connectors, but you could try to look up the pin numbers here: Honda ECU Pinouts Side by Side - Blackworks
 

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Thanks 007 I am getting the ECU flashed after work today so hopefully everything will start working right.
 

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Discussion Starter #5
All good after flash from Honda
Keys work now with the ECU that matches the motor
Only code its throwing was the heater on O2 sensor 2
Wired the Black/Yellow wire to pin 5 yel/blu on connector E
Wired all O2 stuff to connector E and all good now, No codes

So just so its cleared up for anyone else doing a LX - EX conversion in a 2001-2005 Civic here is where the wires are landed when using EX Motor, Trans, Wire Harness and ECU

Here is where they are on the stock harness Connector A (31 pins)
25 wht/red Secondary O2
23 brn/yel Logic Ground
14 blk/wht SecondaryO2 sensor heater control
10 grn/yel Sensor ground
Blk/yel Heater acc power

Here is where they go on Connector E (31 pins)

2 wht/red Secondary O2
3 brn/yel Logic Ground (Shield from O2 Sensor)
5 yel/blu Sensor voltage (attach to blk/yel from O2 Sensor)
6 blk/wht SecondaryO2 sensor heater control
Connector A (31 pin)
10 grn/yel Sensor ground

On the wht/red and Blk/wht
I dissected the old harness to get the whole wire with the metal ends that fit into the harness. As you will find out when going from LX to EX there are a few different wires and they are not in both body harnesses the same way. On the other wires I just tapped in and soldered and taped as not to cut the factory wiring.
I hope his helps anyone that might be doing the same swap that I needed to do to get my everyday driver back on the road with a few upgrades.
 

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Nice job working this out, I am not good at wiring yet. Still cleaning up the old owners mess in my car.

Did you get any pics? Pics help tell the story for sure.
 

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Nice job working this out, I am not good at wiring yet. Still cleaning up the old owners mess in my car.

Did you get any pics? Pics help tell the story for sure.
I will try to take pics before and after I clean up the wiring. Plan on making this look stock.
 

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:TU:
 

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I was just about to post a the same question. I just converted my 02 Civic Sedan from Auto to MT.

Got a complete donor 01 Si. Swapped over Engine, Trans, Engine Harness, PCM, Ignition Tumbler and Transponder.

First startup was a few hours ago, and I ran into the same thing with the O2 Sensors this eve. Was just researching how to wire the sensors directly to the PCM. Only thing I wasnt sure of is where to ground the Signal at PCM. This helps, Ill hopefully get the wiring on this swap finished up tomorrow now.

This is the diagram I was using, from Mitchells Shop key. It just diddnt say anything about O2 Grounds. Just heater + and o2 input.
 

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