O2 sensor pullup resistor values?

[Bernd Felsche]

Peter Florance tapped away at the keyboard with:

> > -----Original Message-----
> > Behalf Of Bernd Felsche

> > Peter Florance tapped away at the keyboard with:
> > > Anyone have any idea of typical ECU pullup resistor (to ~ .45V)
> > > values for O2 sensors inputs? I'm trying to make a analog circuit
> > > to average 2 sensors for my L-jet box and would like to
> > > incorporate it in the front end of the buffers.
> >
> > The "pullup resistors" would be infinite. The sensor is a voltage
> > cell; it provides a voltage. Attempting to bias the sensor can cause
> > damage to the sensor. If you want to level-shift or add/average two
> > sensor inputs, the easiest solution is to use op amps to perform the
> > task. Their high input impedance ensures minimum current draw and
> > sustained operation.
> >
> > > Also interested in any comments regarding averaging O2 sensors for
> > > dual exhaust systems and idle performance (in line 6 engine)
> >
> > Before you go and build a simple adder circuit however, look at the
> > response curves and the consequences of what will happen if one is
> > receiving rich and the other a lean mixture. The ECU needs then to
> > see a constant switching between the levels for correct operation.

> On my L jet box there is some sort of 'bias' that provides .45
> volts at the sensor input before the sensor warms up or if it
> disconnected. I've read that's how they sense whether the sensor
> is working or not.  How do they accomplish that?

Probably on the output of the buffer amplifier, internal to the box.
The sensor's output voltage rises from 0V when it heats up; that
transition may be used to switch off the bias.

You can check this by measuring the open-circuit voltage at the
ECU connector, with the lambda disconnected. 

The sensor can only source a few microamps. Trying to run a sizeable
current through it, which is essential to bias the output directly,
will destroy the sensor.
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