At 11:26 PM 8/23/2011, Dennis Haynes wrote:
>circuit. With nothing connected there is a voltage between the lead
>and ground most likely the bias voltage or forward drop of the
>base-emitter junction. When the O2 sensor is connected before it
>generates it's voltage it acts as a load and sinks this voltage to
>near zero. So yes you can measure a voltage on the O2 sensor input connection.

Dennis, the resistance of a cold sensor is greater than 40 megohms,
so it's not going to load the ECU down any (which is why it stays at
half a volt until the sensor gets hot and begins working).  If you
want me to actually prove it I'll have to trace the circuit, but I'm
confident that the voltage on that lead is placed there deliberately
by the ECU and it's my belief that it's intended to help the ECU
determine when the sensor comes on line effectively, i.e. when its
output is strong enough to overpower the bias coming from the ECU.

>So when the O2 sensor is not connected, this leakage or bias voltage
>is real close to where the ECU would try to adjust it anyway. As
>such it is satisfied and does not make any adjustment. This is why
>leaving the sensor disconnected will often allow the engine to run OK.

If the engine is in proper working order it has no need whatever of
the oxygen sensor.  European vehicles didn't have one - they
couldn't, because Europe was still using leaded gas at the time.  My
'84 was bought in Michigan (but built to California spec), delivered
in Germany and spent the first 87,000 miles of its life with no CAT
and no O2 sensor.  VWOA installed them for me after the Navy shipped
the vehicle over here.  They made a little mistake, since it had been
in Scotland for seven years and according to the paperwork the deal
was only good for three years, but I asked and they said
yes.  Apparently there was a little shouting about that later at VWOA...

The sensor may help a faulty engine run correctly, but if everything
on the engine is correct, the only thing that cares about the sensor
is the CAT.

Yours,
David