Hi Rico,
    You are exactly right,  the 1 and  3 wire o2 sensors like our vans use
have a black wire plus output  to the ecu. The minus side of the o2 signal
is grounded to the o2 case.  The minus signal must travel from the sensor
device assembly,  to the o2 case,  to the exhaust system,  to the engine,
and then to pin 19 of the ecu wiring harness.   This is why the grounds are
so critical on our vans. Digifant pin 19 ground for  the ecu is used by the
ecu adc ( analog to digital converter)  chip as the  ground or minus
refference. for the o2 plus signal. Newer 4 wire  o2 systems have a 4th gray
wire which is the o2 element minus side. The digijet ecu has  no seperate
ground for the o2.   They do still need clean grounds on the left head and
near the coil for proper operation. The digijet ecu  also use the case as a
ground path through the mount to the van frame.

Darrell

----- Original Message -----
From: "Rico Sapolich" <JKrevnov@AOL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Wednesday, November 01, 2000 6:33 AM
Subject: Re: WRONG INFO - O2 Sensor, Bucking, etc.

> Someone recently stated that the O2 sensor is grounded at terninal 19 of
the
> ECU.  This is false.  The active element of the O2 sensor is grounded
> internally through the body of the sensor.  It is only the SHIELD of the
> signal conductor from the O2 sensor to the ECU which is taken to ground
via
> terminal 19.
>
> Rich
>