Insted of trying to re-invent the wheel cant one just remove the cat if that is
what you are trying to do, leave the sensor after the converter in the pipe, and
find the correct value resistor to insert in series or parallel depending on
whether the voltage needs to be higher or lower after the cat a and the computer
will read a voltage an exact percentage higher or lower which ever is correct and
will never know the cat is not working. The voltage will vary in step with the
other sensors. Seems like a simple solution to me.
Jim in Waco
I have some experience with PCMs and OBDII in general, and O2 simulators
> (Basically, the computer compares the readings from the downstream sensor to
> >the upstream sensor,>
> The upstream sensor is defined as the one(s) BEFORE the cat,
> >while the downstream sensor(s) is/are AFTER the cat. The cat functions to
> >REMOVE oxygen from the exhaust, which is what the sensor is looking for. The
> >downstream sensor therefore expects to see LESS oxygen.
> one is a ground provided by the PCM, and the other is a voltage to the PCM (0 to
> 1volts)
> Its been a while since I looked at this stuff but if I remember correctly, 0
> >volts would mean 100% oxygen, and 1 volt would mean 0% oxygen.
> >
> >Exactly the opposite is true. More voltage indicates MORE oxygen.
>
> "Two heated O2S sensors are used. The sensors pro-
> duce voltages from 0 to 1 volt, depending upon the
> oxygen content of the exhaust gas in the exhaust
> manifold. When a large amount of oxygen is present
> (caused by a lean air/fuel mixture), the sensors pro-
> duces a low voltage. When there is a lesser amount
> present (rich air/fuel mixture) it produces a higher
> voltage."
>
> (1996 FSM, page 14-32)
>
> So, I'm working on a module to simulate a downstream O2 sensor behind a
> >functioning cat.
> How are you simulating the exhaust stream without knowing what the
> front sensor is reading? From what you've said, I'm gussing you're
> spitting back a voltage that varies occasionally?
>
> Upstream O2 Vout ------> 10K resistor -------> PCM downstream O2 Vin
> /
> PCM Ground ----> 1K resistor --/
>
> Heating element -----\
> 6 ohm resistor
> Heating element -----/
>
> The voltage output of the upstream sensor would go through a 10,000 ohm
> resistor, while the PCM ground runs through a 1,000 ohm resistor. These
> are joined at the other side, downgrading the upstream O2 sensor voltage
> by approximately a tenth. This voltage is then fed to the PCM via the
> downstream O2 sensor Vout wire in the harness. As far as the heating
> element wires go, I'm planning to stick about 6 ohms of resistance between
> them. (The FSM said that to test the O2 sensor, you should be reading about
> 5-7 ohms between the two wires, so I figured I'd just put the same
> resistance there and maybe it would fool the computer.) Pretty crude
> I know, but I figured it'd be worth a shot?
>
>
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