re: oxygen sensor short to ground

[Johnson David-QA2282 <David.R.Johnson@domain.elided>]

Joe,

the GTV6 has a 1-wire O2 sensor, right?  My guess is that the wire is not
shorted, but is connected to a low impedance input on the ECU, low enough to
appear as a short to your meter.  The O2 sensor generates a voltage between
0 and 1.1 Volts to indicate if the mixture is lean or rich.  Given that is
low voltage and low cureent, I'm a bit suprised that it would be connected
to a low impedance input, but without knowing how the GTV6 ECU is designed
it's hard to comment further.

Many cars actually add a bias voltage to the O2 sensor port, the idea being
that until the sensor heats up and generates a voltage the ECU will see the
bias voltage only and will know that it is an invalid reading and so it will
not close the loop.  I don't know if the GTV6 ECU does this, but since it is
pre-digital it may very well just rely on a timer or engine temp sensor.

I have seen it said that it is actually rather risky to use a multimeter on
circuits which are still connected to an ECU.  This advice usually applies
to an analog voltmeter, which may have a very low input impedance itself and
can draw enough current to blow up the delicate ECU output circuits.  I
would guess that some of the inputs could also be easily damaged by the
voltage and/or current supplied by an ohmmeter.  However, since the GTV6 ECU
is an old analog design, it is probably more robust and this seems less
likely.

The fact that the short dissappears when you unplug the ECU, and is present
in both ECUs, means it is unlikely to be a problem with your wiring harness.
I'd recommend the following webpage for O2 sensor lore and testing
procedures.  I've posted it before and I think it is quite comprehensive,
even though it is from a (gasp!) Chevy Camaro site.  Be warned that I
haven't actually tried the tests they recommend.

http://www.f-body.org/oldfaq/html/tech/sect2.html#oxysensor

Good luck!

Regards,

Dave J.
1987 Milano Verde
1964 2600 Sprint
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