# Bypass a sensor, trick the computer



## CoupeDTS

How do you trick the computer to think a sensor is working? For instance, if there are 2 wires going to a sensor do you stick some sort of resistor or something on the end of the wires? The particular sensor I'm trying to bypass is the o2 sensor. I'm not sure about the spectrum that the sensor senses but I'm guessing it just detects in the exhaust if you are running rich, lean, or normal. So I would want to trick it to think everything is normal. Or is there just a general way to bypass any sensor?


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## cashmoneyspeed

You can't bypass the oxygen sensor with a resistor. It needs to fluctuate voltage and send that signal back to the computer so the engine can keep the air/fuel ratio in the correct range. o2 sensors fluctuate from .1 - .9 volts depedning on a/f mixture. REPLACE it if it's not functioning properly.

Now if your vehicle has o2 sensors after the cat(s) then yes a resistor can be soldered inline to make the computer think it's working and keep the check enging light from staying illuminated. If you have emissions testing, just replace the sensor as you will fail with it like that.


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## CoupeDTS

good info!

we dont have emissions tests here. Im just using new headers that dont have a hole for a 02 sensor so i was wondering how to bypass it. If its left unplugged i wonder how it would react and if it was plugged in and left hanging i wonder how it would react...

also is that how you trick sensor plugs stick a resistor in the end? If so do you know off hand what size resistor?


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## Firefly

> _Originally posted by CoupeDTS_@Sep 1 2009, 05:45 PM~14946514
> *good info!
> 
> we dont have emissions tests here.  Im just using new headers that dont have a hole for a 02 sensor so i was wondering how to bypass it.  If its left unplugged i wonder how it would react and if it was plugged in and left hanging i wonder how it would react...
> 
> also is that how you trick sensor plugs stick a resistor in the end?  If so do you know off hand what size resistor?
> *


Just put the O2 sensor on your new headers? I don't see how that is hard to do?

If you don't use the O2 sensor, or if you feed the computer a constant signal, your car will run like crap. That O2 sensor is there for a reason.


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## CoupeDTS

because the headers are ceramic coated and welding in a port for a sensor (besides being a little difficult and a hassle) is gonna screw up the coating around there. Plus im only trying out this fuel injection i may just go with a carb then i wont need the o2.


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## tearitup

your car will never reach closed loop without the o2 sensor.
It will be constantly injecting fuel like if you were doing a cold start, and the car never got warm.


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## racerboy

my porsche RS/R had a primary and secondary O2 sensor. I had the ecu re mapped to eliminate the need for them. i do not know if your ecu can be remapped, but most can if there is software for it.

some O2 sensors can be tied up and left hanging, but i only know about porsches, so my info may or may not be applicable. try it and see. the worst that will happen is it will run like shit, and/or the CEL (check engine light) will come on


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## cashmoneyspeed

> _Originally posted by tearitup_@Sep 1 2009, 02:05 PM~14948274
> *your car will never reach closed loop without the o2 sensor.
> It will be constantly injecting fuel like if you were doing a cold start, and the car never got warm.
> *


Yup, and the last thing you want for your engine and also perfomance/gas mileage is to stay in 'open loop'.

Buy a new sensor and put it on you new headers and be done with it. 



What engine/car/year?????


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## HARDLUCK88

just get like a 2" section of pipe that fits after the headers and before the cat, weld a bung to it, and splice it in :dunno:


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## Ulysses 2

> _Originally posted by HARDLUCK88_@Sep 1 2009, 05:48 PM~14951017
> *just get like a 2" section of pipe that fits after the headers and before the cat, weld a bung to it, and splice it in :dunno:
> *


 thats the best way


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## MOSTHATED CC

> _Originally posted by HARDLUCK88_@Sep 1 2009, 05:48 PM~14951017
> *just get like a 2" section of pipe that fits after the headers and before the cat, weld a bung to it, and splice it in :dunno:
> *


thats what I would do


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## Ramjunky0978

I have a 1994 Dakota 3.7 liter and the head on my O2 sensor snapped right off. Can I just eliminate it altogether?


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## ctrl

this is what I used, when I gutted my cat. made the check engine light go away, and on the odb2 scanner the sensor is reading normal..

*Converter-Stainless-Catalytic-Extension-Extender*


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## Jenifar

I have a 2003 F150, I bought it without cats, and I think I have two sensors.
I have two questions:
1- Doing as you described will improve mpg?
2- Would this clear the codes automatically?

As your problem, you need a scanner to resolve the issue. A good quality scanner can identify that sensor working or not. *The Autel AP200* could be an easy solution for you.


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