[Gmecm] Can't keep car in closed loop...

[David Allen]

A 4 wire O2 sensor has a separate "clean" ground for the sensor signal, plus
a heating element to improve warm-up time and allow for mounting further
from the heat of the engine.

-The 2 white wires are the Heater.  One should be GND and the other one
should be +12V when the engine is running. Polarity does not matter.  On my
car this is powered off the fuel pump circuit. Do not ground the heater to
the signal "clean ground."
  The white wires from the sensor should have resistance between each other
but no continuity at all to the body of the sensor or to any other wires.

-Gray wire is signal ground. It needs to be grounded to the same point where
the ECM's "O2 signal ground" is terminated. No where else.

-Black wire is the O2 sensor signal.

  If you power the heater off the fuel pump circuit (which is good because
it will only power the heater when the engine is running) remember to
separately fuse for the O2 heater.  It would be a Bad Thing if something as
"unimportant" as the O2 sensor heater shorted out and blew the fuel pump
fuse. This would be a safety problem if it happened on a busy thoroughfare!
IMHO, any wiring that near the exhaust can't be trusted any farther than you
can throw it!
  If it is powered up for several minutes (even without the engine running)
the exterior of the sensor will be hot enough to blister your arm.  Voice of
experience!  Yet another reason to allow the fuel pump circuit to control
it.

Here is a cruddy diagram of how I did it on one of my cars:
http://home.hiwaay.net/~davida1/temp/o2heat.jpg

Later,
David