Rear O2 sensor trick?
 

I recently cut out my cat. since it was non-functional anyway and have been searching and searching for a way to trick the ECU and keep my check engine off. Ive seen the URD resistors and am not interested in paying that much i found a little info on wiring in a resistor and capacitor from radioshack for a few bucks but i am by no means a wiring guru and the little info i found was not enough for me to figure out how to get it done properly. has anyone done this before or know how it can be done that could elaborate and explain a little better for me? I greatly appreciate any info. and please dont tell me just to get a new cat.

Here is a link to a Ford Escort forum posting about how to make a MIL eliminator.
On the Ford Escorts, the only purpose of the second o2 sensor is to check the cat efficiency by looking at the differential between the first and second sensors, and only the first o2 is used for engine/fuel management.
If the Toyota system uses the o2 sensors in the same fashion, this type eliminator might work.
Should'nt be too hard to figure which wire the resistor should go to on your app.

http://www.feoa.net/threads/how-to-m...w-obdii.27076/

Thanks and yes on these 1gen. 4cyl tacomas only the front O2 is used for fuel trim so i would think this will work

Please let us know if you are able to make this mod work for you.

URD is not a resistor, it's a circuit that simulates the signal of a properly working cat/sensor combo.

That stuff is posted by crackpots and doesn't work in theory or practice.

http://mkiv.com/techarticles/oxygen_...tor/index.html

I've built a similar circuit many years ago for under $1 in parts. Identical to a URD. Light never came back. But building that obiously involves having basic knowledge of electronics. If you value your time, it's probably cheaper to buy the URD rather than risking frying your ECU with a DIY solution.

The URD was never an option for over $100 ide rather deal with my check engine light. have you tried the other methods other than the one you posted and had failures?? I ended up basically doing something similar to the info. on the site Millball posted but I used the diagram off of this site: http://www.sr20-forum.com/general-ma...o2-sensor.html
However I followed the actual diagram on that page and not the posters method shown in the pictures. I reset the ECU so I will let you know if the CEL stays off for good

The resistor/capacitor mod is a hack at best. And is not likely to fix the problem long term, if at all. You'll have to look at the output of the sensor and see what is coming out of it. There is a page in the factory service manual that describes how the signal should look like going into the ECU.

If the sensor is bad or the cat is really toasted this won't work. Both of these will the case eventually anyway. So if you piggyback on a bad signal now, and make it acceptable to the ECU using resistors/caps, that doesn't mean the signal will stay bad forever. It will go out completely eventually. That's why the URD and the link I posted do not rely on that. They generate their own signal from scratch. Since you have no cat period, you don't have a signal to piggyback on at all, so the resistor/cap thing won't work anyway.

Well we went on a trail run yesterday it was about 30 miles total round trip and then i had to go to town and back today which is about 60 miles round trip and still no o2 sensor code so i would say the method i used from the diagram I posted earlier has worked and if its good enough to keep the CEL off then its good enough for me... :cheers: :nana:

It takes at least 2 trips to throw that code. That's 1. If you have no cat, the method can't work, period. No chemical reaction is happening where the cat would be and thus the sensor will not put out a sine wave signal that the ECU is specifically looking for.

I realize the ECU is slow and usually takes 2 longer drives to throw a code thats why I said: "trail run YESTERDAY it was about 30 miles total round trip and then I had to go to town and back TODAY which is about 60 miles round trip and still no o2 sensor code" that would be 2 separate trips on 2 different days for a total of 90 miles still no code... :think:

It takes 2 trips just to get the emissions system into ready mode after a MIL reset. Doesn't mean it will show you all existing problems immediately. P0420 can go off for weeks or even months after a reset. But that's for cases with an old cat and old sensor, typical high mileage vehicle scenario. Your's is a 2nd gen 1995 anyway, and no cat, so I can't relate to that. You seem to know what's going on more than me, so you are all set. :laugh:

just a thought. When i had a shop, i used to replace cats with aftermarket ones. When the customers could not afford the best one, i would install a cheaper cat, obviously.

The cheaper cats, and worn out stock cats will cause a cel. When i used these i would install a spark plug non fouler in between the rear o2 sensor and bung. sometimes the head on the o2 sensor would be too big and bottom out on the bottom of the non fouler. the non-foulers came in a pair from the help dorman/motormite section, so i would cut off the second one's threaded section and weld them together to give it more depth.

I have used this more than a half dozen times, and i promise you it works. It pulls the o2 out of the stream enough. I was a skeptic before i did this. It costs a total of $8

meanEG I have heard of this method before and with good success it would be a little tricky sense i have the 2 bolt flange type bung but for now the method in the diagram i posted earlier has worked great it has been about a week now with multiple long drives into town and a couple muddin trips still with no check engine light. So despite some doubts i would say that real life results would prove it successful.

Native American rain dances sometimes prove to be "successful" also. :con:

Obviously you like to bash things that are in your eyes not as good as the way you would do them. I take it you have never tried this method nor read all the success stories with it all over the web? and from your extensive knowledge perhaps you could explain to me why a week and a couple hundred miles later there is still no code if this is simply a "rain dance" then why was my CEL on before and now its not? O ya i forgot because they are all written by "crackpots" that dont even know what an exhaust pipe is i suppose you would consider me one too now since i am another person who has had success with an inexpensive sensor trick. You Sir have a perfect signature

somewhere on yotatech is info on the radio shack fix.

i did this on my 3.4 swap but the scantool does not read the ecm on my truck yet, one of the few things i have to do to finish my swap.

i lost the page i had saved with the diagram when my computer crashed.

Actually... the resistor is a solution if you can find the right resistance.

The ECU is looking for a voltage reading that it is pre-programmed to be a "acceptable". Basically, the O2 sensor is variable resistor. It receives a set voltage and then the electrodes in the sensor will change the voltage based off the reaction from the readings. If it is acceptable (meaning within the programmed range) then there's no light.

The rear O2 sensor is only to confirm that the reading are withing acceptable smog limits. So first off, you're not exactly helping the environment at all by removing your cat. But, if you're set on polluting, you can figure out what resistor you need if you know the input voltage and the correct output voltage readings, as well as the amount of amps the current is drawing. You NEED to know the desired output voltage reading that will make the ECU happy, without that you're just guessing.

You'll need to consult the FSM if you have one and bust out your multimeter (needed to measure amps). To figure out the input voltage and amps, you'll need to connect one end of the multimeter to the wire on the connector providing power, and the other to the return wire to the ECU. You'll then get the current voltage reading (engine must be on, if you haven't figured that out). Then do the same with amps to see how much amps your pulling.

You'll then need to calculate the needed wattage and resistance of the resistor. I hope you passed your physics and algebra classes! Sites like these help: http://www.gtsparkplugs.com/Dropping_Resistor_Calc.html

Once you have the readings for the correct resistor (based off statring voltage, desired voltage, and amps), then go on Ebay/Amazon or your local Fry's/Radio shack and buy the resistor. Plug that into the ends of the connector (where you probed using the multimeter) and if you calculated correctly, no more CEL!

If you read the whole thread I posted a diagram of the inexpensive method I used and how it has worked great, this was several posts back the rest of the thread from there was prety much a pissing match... but thanks for the info. anyway and the concern for all the baby sea turtles my anti-emissions truck is killing.:D

Totally and utterly incorrect information. :laugh:

#1. The ECU is looking for a sine wave voltage sweep, within a proper high-low voltage range, and proper period of the sine wave.

#2. The O2 sensor is not a variable resistor in any sense. It's an O2 sensor, it senses O2 and outputs a low current voltage by itself without any input. It doesn't "receive set voltage". It doesn't "change voltage", and I'm pressure sure it doesn't have any "electrodes". Total misunderstanding of terms and concepts here.

#3. The cat converter is a device inside which a chemical reaction takes place (http://en.wikipedia.org/wiki/Catalytic_converter). It's a cyclical process that burns up the hydrocarbons at a high temperature. That's why a sine wave is generated. It is a very specific chemical process, that with a matched O2 sensor will produce a certain voltage and certain frequency that the ECU is looking for.

I know this thread is six months old, but since I just did this mod, I'll revive it.


My '99 has had the P0420 code ever since I bought it. I would reset the CEL, but it would come back on shortly after. For 2 years I pretty much ignored it, until I ran across a thread describing how to build this MIL eliminator. Went to RadioShack and bought the parts for all of $6, and used heat shrink to make the connections. It's been a week so far I have no codes, not even pending codes. I've made a few long distance drives from Atlanta to Chattanooga, and also to various places around Atlanta. I'll keep an eye on this and see how it goes.