Beretta V6-3100 3.1L VIN M SFI (1995)
PURPOSE
The Heated Oxygen Sensor (HO2S) is essentially a small variable battery; it has the ability to produce a low voltage signal that feeds information
on engine exhaust oxygen content to the POWERTRAIN CONTROL MODULE (PCM).
CONSTRUCTION
The HO2S is constructed from a zirconialplatinum electrolytic element. Zirconia is an electrolyte that conducts electricity under certain chemical
conditions. The element is made of a ceramic material. The element is an insulator when cold. At operating temperature 315°C (600°F), the
element becomes a semiconductor.
A platinum coating on the outer surface of (lie element stimulates further combustion of the exhaust gases right at the surface and this helps
maintain a high operating temperature at the element. The electric heater in the H02S decreases warm-up time and helps maintain operating
temperature at idle. The HO2S has an inner cavity which is filled with atmospheric (reference) air. The atmosphere has approximately 21% oxygen
in it. In the electrical circuit this inner cavity is the positive (+) terminal. The outer surface of the element is exposed to the exhaust gas stream. It is
the negative (-) or ground terminal. Due to the electrolytic properties of the element the oxygen concentration differences between the reference air
and exhaust gases produce small voltages.
OPERATION
A rich exhaust (excessive fuel) has almost no oxygen. When there is a large difference in the amount of oxygen touching the inside and outside
surfaces, there is more conduction, and the sensor puts out a voltage signal above 0.6 volt.
When lean exhaust (excessive oxygen) there is about two percent oxygen in the exhaust. This is a smaller difference in oxygen from the outside
surfaces which results in less conduction and a voltage signal below 0.3 volt. The voltages are monitored and used by the Powertrain Control
Module (PCM) to "fine tune" the air fuel ratio to achieve the ideal mixture desired.
The PCM puts out a reference signal of 0.45 volt. The reference signal serves two purposes. The first is to run the engine when it is in "0pen
Loop" mode of operation. When the air/fuel ratio is correct the PCM "senses" 0.45 volt. When the engine is operating with a rich air/fuel ratio
there is a reduction of free oxygen in the exhaust stream and the H02S voltage rises above the reference voltage. When the engine is run lean, the
voltage drops below the reference voltage due to excess oxygen in the exhaust stream. The HO2S provides the feedback information for the
"Closed Loop" operating mode of the fuel delivery system. The HO2S indicates to the PCM what is happening in the exhaust. It does not cause
things to happen. It is a type of gage: Low voltage output = lean mixture = high oxygen content in the exhaust; high voltage output = rich mixture
= low oxygen content in the exhaust.
An open H02S circuit should set a DTC 13. A constant low voltage in the H02S circuit should set a DTC 44.
