Oxygen Sensor: Description and Operation

GF07.04-P-6100RT Component Description For A O2 Sensor
- up to model year 08

Component Identification:

Location
The O2 sensor upstream of TWC is located in the front area of the oxidation catalytic converter, immediately behind the turbocharger.

Task
The O2 sensor upstream of TWC detects the residual oxygen content in the exhaust and passes on an appropriate signal to the CDI control unit (N3/9).

Design
The O2 sensor upstream of TWC used is designed as a wideband oxygen sensor. The wideband oxygen sensor consists of a pump cell, a concentration cell and a heating element. The heating element maintains the temperature of the ceramic probe body constant at 780 °C. The conductivity of the ceramic probe body is temperature dependent.

Function
The exhaust passes through a gas inlet hole in the pump cell into the measuring chamber of the concentration cell. The oxygen from the exhaust is pumped into a reference chamber which serves as the oxygen reference. Applying a voltage to the platinum electrodes of the pump cell allows oxygen to be pumped in or out of the measuring chamber. An analysis module in the CDI control unit controls the voltage applied at the pump cell in such a way that the mixture composition in the measuring chamber is set constant at the value lambda= 1.
For lean exhaust oxygen is pumped out of the measuring chamber through the pump cell. The pump current is therefore positive. If, on the other hand, the exhaust is rich then oxygen at the platinum electrode is pumped due to the catalytic decomposition of carbon dioxide (CO ) and water out of the exhaust of the environment into 2 the measuring chamber. The pump current is therefore negative. If lambda= 1 exists in the measuring chamber then no oxygen will be transported. The pump current in this case = 0 mA.
The respectively required pump current is the measure for the air/ fuel ratio lambda and is processed in the CDI control unit for the corresponding functionality.