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How To: Wiring secondary o2 sensor directly to ecu

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Old 02-24-2009, 11:13 AM   #1
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Icon6 How To: Wiring secondary o2 sensor directly to ecu

I have spent a lot of time researching this topic, and it seems as though there are a lot of people like myself looking for this information. I am not the best when it comes to wiring, so maybe that is why it was so hard for me to figure out, or maybe this is just something that everybody else just inherently knows this information. Either way, it seems to be a problem, and this is the solution.

The Problem
If you own an EK that did not come from the factory with VTEC and you decide to swap in a vtec motor, you have a couple of options when it comes to the harness. You can:
1. use your stock DX/other harness, and wire in VTEC, and do whatever other mods needed for your specific swap.
2. use an EX/SI harness, this way everything is already wired in (or so you think)

The problem if you use an EX/SI harness is that although everything is wired in, you will be missing your secondary o2 sensor. This is because in an EX/SI car, the secondary o2 sensor comes from the cabin harness that is attached to the car itself, and your DX car will not have the connection.

The Solution
If you have decided (like myself) to get the EX/SI harness thinking that there will be no wiring, you can do one of the following:
1. buy and install the cabin harness from an EX/SI with same OBD2x version as your car/engine harness/ecu.
2. Wire the secondary o2 sensor directly to your ecu. This is the route I decided to go, because i thought it would/should be easier than finding/installing the cabin harness.

The Wiring
So on your o2 sensor, you should have 4 wires and they should be:
1 green wire (this is the SENSOR ground)
1 white wire (this is the sensor signal wire)
2 black wires (these have been labeled as the "Heater wires")

All you need to do is wire THREE wires to the ECU. That's right, THREE wires, not four! Here's what you do:
This pertains to OBD2a only]
Green wire (signal wire) = D13
White wire (sensor wire) = D14
1 Black wire (heater wire) = A6
1 Black wire (heater wire) = some 12v lead. you could wire this to the battery directly (if that's what you want to do), I wired it to a 12v that got hot with the key on only. This way it couldn't pull power with the key in the OFF position. From what I understand, the two black wires create a circuit, one needs 12v the other needs a ground? -something like that- I constantly referenced this site http://technet.ff-squad.com/wiring.obd2a.htm for information.

This info should work for an OBD2b, given that you research and find the correct pin locations for your car. http://technet.ff-squad.com/index.htm has the pinout schematics for OBD2b, it should be something like:

White = A23
Green = C18???? (not sure if this is correct, somebody pls verify)
Black = A8
Black = 12v lead

Hopefully this information helps somebody.....
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Old 02-27-2009, 08:29 PM   #2
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

Quote:
Originally Posted by DeucesWild View Post
I have spent a lot of time researching this topic, and it seems as though there are a lot of people like myself looking for this information. I am not the best when it comes to wiring, so maybe that is why it was so hard for me to figure out, or maybe this is just something that everybody else just inherently knows this information. Either way, it seems to be a problem, and this is the solution.

The Problem
If you own an EK that did not come from the factory with VTEC and you decide to swap in a vtec motor, you have a couple of options when it comes to the harness. You can:
1. use your stock DX/other harness, and wire in VTEC, and do whatever other mods needed for your specific swap.
2. use an EX/SI harness, this way everything is already wired in (or so you think)

The problem if you use an EX/SI harness is that although everything is wired in, you will be missing your secondary o2 sensor. This is because in an EX/SI car, the secondary o2 sensor comes from the cabin harness that is attached to the car itself, and your DX car will not have the connection.

The Solution
If you have decided (like myself) to get the EX/SI harness thinking that there will be no wiring, you can do one of the following:
1. buy and install the cabin harness from an EX/SI with same OBD2x version as your car/engine harness/ecu.
2. Wire the secondary o2 sensor directly to your ecu. This is the route I decided to go, because i thought it would/should be easier than finding/installing the cabin harness.

The Wiring
So on your o2 sensor, you should have 4 wires and they should be:
1 green wire (this is the SENSOR ground)
1 white wire (this is the sensor signal wire)
2 black wires (these have been labeled as the "Heater wires")

All you need to do is wire THREE wires to the ECU. That's right, THREE wires, not four! Here's what you do:
This pertains to OBD2a only]
Green wire (signal wire) = D13
White wire (sensor wire) = D14
1 Black wire (heater wire) = A6
1 Black wire (heater wire) = some 12v lead. you could wire this to the battery directly (if that's what you want to do), I wired it to a 12v that got hot with the key on only. This way it couldn't pull power with the key in the OFF position. From what I understand, the two black wires create a circuit, one needs 12v the other needs a ground? -something like that- I constantly referenced this site http://technet.ff-squad.com/wiring.obd2a.htm for information.

This info should work for an OBD2b, given that you research and find the correct pin locations for your car. http://technet.ff-squad.com/index.htm has the pinout schematics for OBD2b, it should be something like:

White = A23
Green = C18???? (not sure if this is correct, somebody pls verify)
Black = A8
Black = 12v lead

Hopefully this information helps somebody.....

Worked. Thanks!
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Old 03-04-2009, 02:48 PM   #3
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

np.... figured that it would help somebody, considering i beat my head against the wall trying to figure it out
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Old 03-04-2009, 03:06 PM   #4
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

It worked for a day then my cel came back on

but I reset it again, so far it has worked for 1 full day again lol
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Old 03-06-2009, 11:53 AM   #5
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

anyone have an idea as to why it would come back on after a day?
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Old 03-06-2009, 12:59 PM   #6
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

maybe becasue it's missing 1 wire???...lol just a thought...
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Old 03-06-2009, 01:46 PM   #7
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

Quote:
maybe becasue it's missing 1 wire???...lol just a thought...
there is only room for 3 wires on an obd2a ecu...... not to mention that this DOES clear the CEL, yet Malfa had the CEL come back after only 1 day of driving.

next time read the thread before posting ignorant bs, thanks.


TTT for somebody with some actual insight
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Old 03-09-2009, 01:15 PM   #8
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

I keep resetting it and then it comes back within 1 or 2 days. Lame!
When I have time I will check wiring again...
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Old 03-16-2009, 05:09 PM   #9
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

man i cant tell you how long ive been looking for this answer!!! thank you and im gona dive in and see if i can fix mine also. ill post and let you know how it goes. THANK YOU!!
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Old 03-26-2009, 08:29 PM   #10
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

im having the same issue, after a day or so of driving the check engine light keeps coming on.
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Old 03-31-2009, 05:05 PM   #11
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

can anyone share some insight as to how to fix this problem permanently???
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Old 04-05-2009, 11:00 PM   #12
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

Bump
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Old 04-16-2009, 01:10 PM   #13
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

ttt
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Old 04-16-2009, 03:33 PM   #14
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

ttt for some help
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Old 04-17-2009, 10:28 AM   #15
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

anyone?
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Old 05-13-2009, 08:38 PM   #16
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

Hey I am having this problem 65-secondary o2 sensor heater wire..

My car is a 96 dx with an EX harness just like you..

I am about to wire the sensor straight to the ecu but wondering if you guys are still having issues with the cel coming back on intermittently??

Also, how exactly did you pin the wires into the ecu connector? Do they just stick right into it?
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Old 07-02-2009, 03:58 PM   #17
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

Quote:
Originally Posted by DeucesWild View Post
anyone?
well if your tryin gto do the secondary o2 this way shouldnt you use a5 for the heater wire and not a6. pinout says a6 is for the primary o2 not secondary
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Old 08-06-2009, 11:28 AM   #18
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

has anybody done this to an obd2b? Bump for info.
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Old 09-05-2009, 04:15 PM   #19
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

Can anyone verify the obd2b info DeucesWild posted? white=a23, green=c18, black=a8? Just put a b16a2 in my 99 hatch and this is the only thing I'm unsure of
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Old 09-05-2009, 08:47 PM   #20
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

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Originally Posted by echoside View Post
Can anyone verify the obd2b info DeucesWild posted? white=a23, green=c18, black=a8? Just put a b16a2 in my 99 hatch and this is the only thing I'm unsure of
you need 4 wires. Here is what I did on my 99 sedan with b16a2 obd2b

http://ff-squad.com/wp/?p=395
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Old 09-06-2009, 04:05 AM   #21
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

You're the best sir ash
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Old 11-09-2009, 12:05 PM   #22
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

old but arent you supposed to wire the heater ground to a5 not a6
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Old 11-09-2009, 05:52 PM   #23
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

Yes it's actually a5, the link sir ash provided has the correct wires listed for obd2a and obd2b.
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Old 01-16-2010, 04:18 PM   #24
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

I'm also having this issue with my 98 EX engine i swapped into my 99 DX car. I'm using a 99 EX engine harness so now i need to wire in the second O2 sensor. I had just finished extending the wires and was going to install them into the ECU connectors, when i noticed there are already wires in the same location in the ecu connector where i'm supposed to wire the sensor into. So im wondering if i have to remove the wires already in it, but im not sure if it will cause any problems. Or should i just splice into them, but again i dont know if it will cause any problems.
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Old 02-15-2010, 11:23 AM   #25
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Default Re: How To: Wiring secondary o2 sensor directly to ecu

Has there been a clearcut fix for this issue?
I am using OBD2a..

I also need to wire up my rear 02 sensor..

I clicked on the link sir ash posted and I got a virus warning..
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