Date:         Thu, 4 Feb 1999 23:39:14 -0500
Reply-To:     EMZ <vw4x4@FYI.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         EMZ <vw4x4@FYI.NET>
Subject:      All you ever wanted to know about O2 sensors
In-Reply-To:  <3.0.32.19990204212822.00686984@mail.ipns.com>
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Anyone who was talking about cooking on you engine:
       HIT THE DELETE KEY NOW


         Understanding the Oxygen Sensor

Mounted in the exhaust stream, the oxygen sensor is used by
the vehicle's on-board computer to verify that programmed fuel
delivery is matching the engines fuel requirements. The more common
oxygen sensors generate a voltage between 0.0 and 1.0 volt DC
depending on the amount of oxygen present in the exhaust after
combustion occurs.

There are three popular types of early oxygen sensors:

1 - The single wire. The single wire connects to the wiring harness
which in turn is connected to the ECU. The negative side of the sensor
is grounded through the shell of the sensor which is grounded through
the exhaust manifold.

2 - The two wire. This sensor remains the same as the single wire
except the second lead wire is a dedicated ground circuit returning to
the ECU. It also has a ground path through the sensor shell.

3 - The three wire. This sensor incorporates a heater element to bring
the oxygen sensor up to operating temperature faster. This improves
the fuel economy during cold weather operation and short drive cycles.
The signal remains the same as the one wire sensor. The sensor is
grounded through the case. There are two white wires for the heater
and are isolated away from the sensor signal circuit. Power to the heater
is usually provided from the fuel pump circuit. The heater ground path
is to the chassis.

Recent additions to the Oxygen Sensor family:

4 - Three wire (II). Utilizing a sensing element made from titanium rather
than zirconium this design of oxygen sensor does not generate a voltage
as the exhaust goes rich and lean. The sensing element acts more like a
transistor in that it switches a reference voltage supplied by the ECU on
and off to ground as the exhaust goes rich and lean. Found most commonly
on late 80's Jeeps with Renix ECU along with a few far eastern exotic vehicles,
both 1 and 5 volt versions are used. Application and usage are very distinct
on this sensor design. This sensor has one signal wire to the case as
ground, and also has a heater two white wires use by a heater.

5 - The Four wire. The latest version of the conventional oxygen sensor,
the signal lead and the heater circuits remain the same as in the early
three wire sensor but have  been joined by a fourth dedicated signal
ground. The dedicated ground was added to ensure corrosion on the
sensor case and exhaust manifolds do not create a false signal.

6 - Four wire (II). Mounted behind the catalytic converter this newest addition
is used by OBD II equipped vehicles to montitor converter efficiency. Basically
the same as the regular four lead sensor, with minor variations to the
lean-rich switching point along with physical changes to accommodate the
mounting location.






            Eric                   86-VW4x4
            vw4x4@fyi.net          72-240z
            Pittsburgh, PA USA     1936-Chrysler