Confirming the 10 MegaOhm O2 sensor work around - Honda Prelude Forum

Topic7 · 01-24-2004, 10:36 PM

I recently got a test pipe and as soon as I turned my car on the saw that wonderful check engine light come on. Pissed me off for sure but I spent the last two weeks reading up on the subject (on po.com and other websites) and I came across the concept of hacking into the O2 sensor wires and inserting a resistor to imitate the voltage that the O2 sensor senses when the car correctly makes "clean" exhaust fumes.
I know that there are other ways to trick the ECU but I didn't feel like spending $30 on a stupid O2 sensor imitator or whatever those devices are that trick the ECU. So I took my chances and went to radio shack and bought me the supplies and did the hack. I'm pleased to say that this "myth" actually solved my problem and the check engine light is no more in my car.
So as a tribute to all of you who are scared to do it, heres my super quick mini writeup with diagrams only on how to trick your O2 sensor in believing that your exhaust is nice and clean.

Materials:
1) wire cutters
2) wire strippers
3) 1 10 Mega Ohm resistor rated at 1/4 watt or more. - Radioshack P/N 271-1365
4) 2 Butt Connectors - Radioshack P/N 64-3108
5) Clear or Gray Heatshrink that is 1/4x6" or larger, but I found this to be the best size. - Radioshack P/N 278-1610
6) A heatgun or lighter or anything that will make the heatshrink actually shrink.
7) electrical or duct tape/zip ties.

Procedure:
1) get under the car and disconnect the REAR O2 sensor from the socket and from the cat. To disconnect it from the cat is a bit tricky and a special tool is needed. You can get it done at a muffler shop for little to nothing. Instead of trying to think up a good excuse simply tell them that your getting a new cat and that you need to take the O2 sensor out to put it in the new one or you can tell them that the sensor went bad and your replacing it. Anyway, if you don't have the tools to get it off the cat then get some place to do it.

2) assuming that the sensor is off the car and out of the cat your next goal is to expose some of the gray wire, i believe that there are either three or four wiress, a black, 2 whites, and a gray, I THINK. Regardless there is still a gray wire.

3) cut the wire and strip about 1/4-1/2 inch on each side of the gray wire. This gap is where your resistor will go.

4) take out 1 10 MegaOhm resistor and simply insert one end into the butt connector. Then take the gray wire that you just cut (Doesn't matter which side) and insert that into the butt connector and crimp both sides. Now give a light tug to ensure that both the resistor and the wire are both secure.

5) Now slide the heat shrink over that piece and expose the other end of the resistor, the one that hasnt been connected.

6) repeat step 4 except do it with the other side of the resistor and the other side of the wire. Now crimp. There is no wrong way to put in a resister so don't stress out about putting it in in reverse, cause it can be connected both ways.

7) slide the heatshrink so that it covers the whole area that has been worked on and so that it overlaps the factory black wire
hose.

8) Now take your heating device and slowly heat the heatshrink so that it shrinks over the resistor and the two butt connectors. This makes sure that no metal or connection of any kind will losen or make contact with the frame or any other part of the car.

9) Take the electrical tape or duct tape and wrap it around the whole O2 sensor cable, or atleast the part the has the heatshrink on it. I wrapped electrical tape around the whole O2 sensor cable.

You should now be done and ready to role! Don't forget to plug the O2 sensor back in the car and you have to disconnect the battery from the car for a second from the car so that the computer will reset. Then just zip tie or duct tape the sensor and the wires to the frame and should be good to go!

Below is a diagram of what a butt connector looks like:

Butt Connector
$1.69
Catalog #: 64-3108

Below is what the resistors look like:

10M ohm 1/4W 5% Carbon Film Resistor pk/5
$0.99 Brand: RadioShack
Catalog #: 271-1365 Model: 271-1365

Below is a diagram of what the heatshrink looks like: The one that I used was the largest clear sized one that came in this pack:

Multicolor Heat-Shrink Tubing
$2.49 Brand: RadioShack
Catalog #: 278-1610 Model: 278-1610

This final diagram is a view of what I just explained should look like:

Don't forget to put tape over this whole deal.

Good luck to everyone, I hope that it is as much of a success for you as it was for me. If you have any questions, comments, or problems let me know.
Hack on my lude brothers!

checkmate58 · 01-24-2004, 11:53 PM

This is a great writeup. Props to you. So does that mean that if they plugged to run a diagnostic, would it detect the hack or just believe that the O2 sensor is working fine?

--Sam

alphajesse · 01-25-2004, 12:39 AM

It should show up like a normal secondary o2 sensor

Topic7 · 01-25-2004, 10:41 AM

I bought another O2 sensor wire and when inspection time comes around i'll put the cat back on and use the unhacked O2 sensor wire to pass inspections.

B0b · 01-25-2004, 12:37 PM

you own!

NotoriouSH · 01-25-2004, 01:06 PM

First of all, you don't need an exhaust shop or a special tool to unscrew the O2 sensor. I have swapped my cat/testpipe on 3 occasions and each time I have used an adjustable wrench without any effort required.

Secondly, there are a lot of people on here who will take your writeup word for word (just look at the NTPOG OBDII workaround â€“ most people don't realize that cutting the wire will produce the same effect as wiring in an on/off switch). SO my recommendation is to just simiply tell people to splice in the connector however they see fit. I personally will not use a butt splice, I believe soldering is the best method but to each his own.

How did you determine the correct resistor? It's an extremely simple solution to a tremendously complicated problem, and you did it just by doing your homework â€“ mad props dude!

I don't mean to criticise your post, I am insanely happy that you figured it out! I'm just saying that this mod will no **** take a normal person 5 minutes to complete, but you're writeup includes all these extra instructions that make it seem complicated.

For those of you with mechanical and electrical knowledge who know how to do this sort of stuff:

Parts:
1 10 Mega Ohm resistor rated at 1/4 watt or more. - Radioshack P/N 271-1365

Procedure:

1) Get under the car and disconnect the REAR O2 sensor from the socket and from the cat.

2) Splice the10 MegaOhm resistor into the grey wire.

3) Reconnect O2 sensor

AsianPersuasion · 01-25-2004, 01:58 PM

^^^ I just wanted to say that it's a great writeup for those who have NO mechanical/electrical know-how. It may be a little over zealous in writing, but it's incredibly useful for those who want to know every little detail and I commend him for doing so.

Good job Topic7... keep it up.

Topic7 · 01-25-2004, 04:17 PM

i based my writeup on the fact that even though i an mechanically and electronically knowledgeable i still read every detail so i saw it fit to include everything i could possibly think of. In terms of connecting the wires to the resistor, i assumed that not many people have a soldering gun and that this is in my opinion a solution that will work just as good. So if you want to solder it then feel free but I think that using the butt connectors is a solution that still works just as well and uses less effort. It's your choice, I did the writeup based on what I would do.

pIOUs · 01-25-2004, 05:03 PM

This writeup covers all bases and serves the broader PO.com community, but thanks for the cliff-notes NotoriouSH.

It's always hard to decide how much detail is necessary to express the job. Too quick and there are tons of questions that take away from the writeup...too long and people get put off by the seemingly hard task. It's funny how this may have been mentioned in a post before, but until it was re-writen as a writeup, most probably missed it. I know this has been discussed in theory in diffused conversations, but I like this thread. Good job for trying this out and writing about it Topic7

NXLude · 01-25-2004, 05:53 PM

As it was said, how did you decide the proper ohms? I think this would be a good thing to do if your using a vafc also, it wont let the computer see anything to adjust....

2000scSH · 01-26-2004, 12:43 AM

I know that there are other ways to trick the ECU but I didn't feel like spending $30 on a stupid O2 sensor imitator or whatever those devices are that trick the ECU.

Where can i get one of those O2 sensor imitor or a dummey sensor & would one of them be easier ????

Si4WS · 01-26-2004, 12:34 PM

FAQ Please!

I must say, great idea, and I'm going to do this, but should I worry about air/fuel, I may want to run a 2 bung test pipe, one o2 sensor running with the resistor inline going to the ECU and one to an A/F gauge to monitor the mix? Or does this only affect floral (sp?) carbons or something?

Topic7 · 01-26-2004, 02:05 PM

Quote:

Originally posted by Si4WS
FAQ Please!

I must say, great idea, and I'm going to do this, but should I worry about air/fuel, I may want to run a 2 bung test pipe, one o2 sensor running with the resistor inline going to the ECU and one to an A/F gauge to monitor the mix? Or does this only affect floral (sp?) carbons or something?

I don't know the whole answer to your question but i've been doing some research and it looks like out O2 sensor works by sending between 0 and 1 volts to the ecu. Below is a graph that shows how the ecu knows how rich or lean it is based on the voltage it receives from the sensor.

as you see the simulate a perfect mix, I think you would need to drop .5 volts to make it ideal, or to get it at 14.7:1.

Quote:

Originally posted by 2000scSH
Where can i get one of those O2 sensor imitor or a dummey sensor & would one of them be easier ????

[/B]

here are a few links to O2 sensor simulators:
http://www.defcon-racing.com/o2sim.html
http://www.zzperformance.com/zzp/pro..._simulator.htm <--- best price

looks pretty easy to install, plug the O2 sensor into this thing and then plug this thing into the plug that goes to the ecu and your done.

Also since I have a VAFC I can get the richness or leanness (is that a word?) tuned out of it so as long as the CEL stays off I'm happy.

NXLude · 01-26-2004, 03:40 PM

Well, according to ZZ site, the secondary sensor doesnt do much. I wonder if this same thing could be done with the first sensor to keep the ecu from modifying the fuel after it was tuned. Anyone know if this is possible

alphajesse · 01-26-2004, 07:29 PM

You can get away with this on the secondary o2, as it pretty much is there to confirm the cat is working properly, and nothing else.
You put this on the primary o2, and it will basically make your car run (super) rich all the time.

Hobie1113 · 01-26-2004, 08:40 PM

right, if you're stock. But what if you have a VAFC or some other type of fuel management system. Wouldn't this allow you to set the O2 Sensor voltage at a constant for the most part and then base the maps completely off of what you set it to be. In other words, no ECU intervention in the fuel maps.

NotoriouSH · 01-26-2004, 08:56 PM

The O2 voltage on the first sensor fluctuates with what it detects in the exhaust stream. By splicing in a resistor, all you are doing is impeding a signal that is already constantly changing. It will do nothing except ruin your car's ability to compensate for rich/lean conditions. With normal driving your ECU already tunes for stochiometric, it's the WOT maps on the ECU that are the problem and those do not use the signal from the O2 sensor anyway (closed loop operation).

alphajesse · 01-26-2004, 09:33 PM

^, yeah, and if you replace it with something to provide the ecu with a constant .5v signal, you'll get a primary o2 sensor CEL. It is expecting fluctuation from the o2 sensor while in closed loop.

NXLude · 01-26-2004, 11:14 PM

I just wonder if you could emulate a proper voltage on the first one so you can tune it youself. Even if the car ran really rich you could just pull some out with afc. I ask this because when i tune my car shortly I need to do something at part throttle to get the car running smooth witht he new setup. I can tell that the ecu has done what it can to get the car to run/idle, but its not enough. I gotta get the car to smoth out some. I just dont want the stupid ecu changing my part throttle settings. I need to figure this stuff out.

alphajesse · 01-27-2004, 12:50 AM

Get hondata or equivilent.