Sprinter 2500 V6-3.0L DSL Turbo (2008)
The sensor cell measures the difference between the oxygen concentration in the gas sample chamber and the oxygen concentration in the outside air
from the reference air channel. A small voltage is generated across the sensor, which is proportional to the air-fuel ratio in the sample chamber. At
stoichiometric ratio (14.7 lbs. of dry air to 1 part fuel), the corresponding open circuit voltage at the sensor cell is 450 mV. If the stoichiometric ratio in
the sampler chamber is higher than 1 (excess air) a lower voltage is produced. If the stoichiometric ratio is lower than 1 (insufficient air) a higher voltage
is produced.
The ECM uses this voltage signal to determine how and when to run the oxygen pump cell. The goal of the ECM is to modulate the pumping current
through the pump cell to always maintain stoichiometric air-fuel ratio (14.7 to 1) in the gas sample chamber. When stoichiometry is reached, there is no
current flowing to the oxygen pump.
High Excess Air Mode
When the exhaust gas is too lean, the oxygen concentration in the gas sample chamber is high. The sensor cell measures the difference between the
oxygen concentrations in the sampler chamber and the reference air channel. A voltage lower than 450mV is generated across the sensor cell, which is
proportional to the air-fuel ratio in the sample chamber. The ECM compares the sensor cell voltage with the reference voltage (V Ref), which
corresponds to the stoichiometric point voltage. Since sensor cell voltage is lower than V Ref, the ECM determines a lean condition exists. Am amplifier
applies an appropriate voltage to the pump cell to transfer oxygen from the gas sample chamber
Low Excess Air Mode
With low excess air mode, the oxygen concentration in the gas sample chamber is low. The sensor cell measures the difference between oxygen
concentrations in the gas sample chamber and the reference air channel. A voltage higher than 450 mV is generated across the sensor cell, which is
proportional to the air-fuel ratio in the sample chamber. The ECM determines a low excess air condition exists. The polarity of the pump cell is reversed
and so is the direction of the current flow.
