the O2 sensor can be removed (unplugged) to test drive the car.
to see if it runs better.(unplugged the volts go to steady 0-.45vdc. )
the 02 will read wrong if there are exhaust pipe cracks anywhere near the 02 sensor.
causes the 02 to slam to 0vdc output and EFI goes full rich, even fouling spark plug tips black.(seen)
do short drives,
if running too rich the CAT can even melt.
so test for short drives. only.
the 02 sensor , this year , only tests , with a scope work,
here is OBD2 doing, a simulated 02 scan plot, the O2 output swings fast. (real data on real car) not this car. on 1996+ up.
that swing is the PCM trimming fuel on the fly, fast. 6 times second possible
it swings so fast this cheap tool can not see all the swings, but we know it did
you can not do this with OBD1, nobody sells a RENIX tool.
this 02 can show bad all these ways
below is good photo.
it can be dead the O2 output pin.
stuck high
stuck low
or shifted high or low failed.
with 02 working mPG goes to max. << this is why we want it so.
