doctorbull

So i was reading this DIY for how to install a Diode in the rear O2 sensor wiring so that the ECU sees the voltage it wants, assumes the cat is fine, and then stops giving "efficiency below threshold" codes:

https://www.audiworld.com/tech/eng53.shtml

and then stated reading this post about how to check the O2 sensor pins to see if your sensor is working, and what each pin does:

https://www.audiworld.com/tech/eng101.shtml


so what i am wondering is, does anyone know if it would be possible to simply clip the sensor harness leaving only a little bit of wire behind the connector, then connect those wires together in such a way that with the right diode/resistor combination inbetween them the ECU sees the voltages/current it wants, and assumes a correctly working, properly functioning o2 sensor is present and detects a working cat, when in fact it is not?

basically physically removing the whole rear o2 sensor completely? Plugging in a "fake" o2 sensor, and then just putting a plug in the 02 sensor exhaust bung?

anyone have any insight, ideas, or knowledge on the situation? if it would work, or why it would/does not work.

in theory it would be great, no fault codes, no codes caused by its absence, and one less wire bundle cluttering up the engine bay

4Driver4

It's not that simple. The ECU won't fall for that. It looks for delta between front and rear, so the value it looks for from the rear sensor varies with what it sees from the front sensor.

doctorbull

thats what i thought too, but according to the AW writeup listed in the first link it makes it sound like that is not the case

doctorbull

but i see what you are saying, that instead maybe the ecu is looking for a signal out of the post cat sensor that is some lowered factor of the precat signal, right?

so instead of this like (how i thought the first article was explaining it):
Precat Voltage___PostCat Voltage
___1.2______________.45
___1.8______________.45
___2.2______________.45
___2.8______________.45
___4.9______________.45

The ECU wants to see something like this where there is a consistent difference between the two (in this example post cat signal is .5 volts less than the pre cat signal):

Precat Voltage___PostCat Voltage
___1.0______________.50
___1.5______________1.0
___2.0______________1.5
___2.5______________2.0
___4.0______________3.5


or maybe the second value has to be some percentage of the first value, like this (in this example postcat signal is 50% of the precat signal):

Precat Voltage___PostCat Voltage
___1.0______________.50
___1.5______________.75
___2.0______________1.0
___3.0______________1.5
___4.2______________2.1

Does anyone know what it is?

I wondering if you could just take the precat sensor signal, and splice it and drop that voltage by some constant or factor and use the new dropped voltage line as the "post o2 sensor" output, and use a diode to make sure that new voltage value only goes one way (to the ecu and then keeps from messing up the precat sensor signal)?

doctorbull

this guy claimed he was able to build one too, but the site he bought his parts from claims the EPA made them stop selling the kit components

https://www.audiworld.com/forums/sho....php?t=1574487