O2 Sensor current?

[Wen Yen Chan]

Hello,

A while back I tried to offset the reading from my O2 sensor with a simple
op-amp circuit. The circuit worked fine but the ECU always thought the
sensor was hot (even after a cold restart). It seems that the Honda ECU I
was playing with pulled a small current from the sensor to check if it was
lit. When my circuit was added the ECU saw the low output impedence of the
op-amp and just assumed the sensor was hot. 

Wen


On Wed, 24 Mar 1999 Teller.John at orbital.com wrote:

> O2 Sensors do not draw current (excepting the heater in a heated 02
> sensor), they are in fact a voltage source.  Not only that, they are a high
> impedance voltage source and therefore do not put out much current at all.
> The voltage drop through a 10K resistor is going to be negligible due to
> the miniscule currents (less than a microAmp) involved.  To figure the
> voltage drop accross your 10K resistor, use Ohm's law (E=I*R) where I =
> 0.0000002 Amps and R = 10000 Ohms for a voltage drop of 0.02 Volts.
> 
> If you want to change the output voltage of one of these devices, you
> probably would be better off using an op amp circuit with a gain factor
> less than 1.  Any loading of the output of these devices will at best
> provide erroneous readings and at worst destroy the sensor.  See the
> Forrest M. Mims books which are (or at least used to be) available from
> Radio Shock for some examples of these circuits.
> 
> 
>