O2 sensors, component description - GF07.04-P-6100VA

ENGINE 272.920 in MODEL 203 up to Model Year 8

ENGINE 272.922 in MODEL 211 up to Model Year 8

ENGINE 272.940 in MODEL 203 up to Model Year 8

ENGINE 272.941 in MODEL 203 up to Model Year 8

ENGINE 272.942 in MODEL 171 up to Model Year 8

ENGINE 272.943 in MODEL 211, 219

ENGINE 272.944 in MODEL 211

ENGINE 272.945 in MODEL 251 up to Model Year 8

ENGINE 272.946 in MODEL 221 up to Model Year 8

ENGINE 272.960 in MODEL 203 up to Model Year 8

ENGINE 272.963 in MODEL 171 up to Model Year 8

ENGINE 272.964 in MODEL 211, 219

ENGINE 272.965 in MODEL 221 up to Model Year 8

ENGINE 272.966 in MODEL 230 up to Model Year 8

ENGINE 272.967 in MODEL 164, 251 up to Model Year 8

ENGINE 272.970 in MODEL 203 up to Model Year 8

ENGINE 272.972 in MODEL 211

ENGINE 272.975 in MODEL 221 up to Model Year 8

ENGINE 272.985 in MODEL 211, 219

ENGINE 273.922 in MODEL 221 up to Model Year 8

ENGINE 273.923 in MODEL 164 up to Model Year 8

ENGINE 273.924 in MODEL 221 up to Model Year 8

ENGINE 273.960 in MODEL 211, 219

ENGINE 273.961 in MODEL 216, 221 up to Model Year 8

ENGINE 273.962 in MODEL 211

ENGINE 273.963 in MODEL 164, 251 up to Model Year 8

ENGINE 273.965 in MODEL 230 up to Model Year 8

ENGINE 273.967 in MODEL 209

ENGINE 273.968 in MODEL 221 up to Model Year 8

ENGINE 272.940 in MODEL 209

ENGINE 272.960 in MODEL 209

Shown on engine 272.963

Fig 1: Locating Catalytic Converter And O2 Sensors

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Location

Engine 272 CIS-E: The O2 sensors downstream TWC are bolted onto the side of the catalytic convertors. They are located in the space between the first and the second monoliths.

Engine 272 DE: The O2 sensors downstream TWC are bolted into the exhaust pipes downstream of the catalytic converters.

Shown on engine 272.963, right cylinder bank

Fig 2: Identifying Catalytic Converter And O2 Sensors

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Task

The O₂ sensors downstream of TWC (guide or diagnostic sensors) are designed as planar oxygen sensors and detect the residual oxygen content in the exhaust gas for the following tasks:

Two-sensor control
Monitoring of catalytic converter efficiency.

Design

Fig 3: Identifying O2 Sensor Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Connector for O ₂ sensors downstream of TWC, round and square version (View of connector on O ₂ sensor)

Fig 4: Identifying O2 Sensor Connectors

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Voltage-free insulated O₂ sensors are used.

The active sensor ceramic consists of a gas permeable ceramic body made of zirconium dioxide. A protective tube with several slots protects the ceramic body from mechanical stresses and from temperature jumps.

They are connected electrically by means of a 4-pin connector.

Advantages of planar sensor compared to finger sensor:

Stable control characteristic
Reduced overall size
Quick start (control readiness<10 s)
Reduced heating capacity at operating temperature (< 7 W)
Increased temperature resistance.

Functional principle

Fig 5: Identifying O2 Sensor Function

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Function

The sensor ceramic is conductive for oxygen ions from approx. 300°C. If the oxygen concentration on both sides of the sensor ceramic differs, a voltage is produced at the boundary surfaces as a result of the particular properties of the sensor ceramic (Nernst voltage). This Nernst voltage produces the O₂ sensor signal, which is a measurement for the residual oxygen content in the exhaust gas.

The evaluation circuit of the O₂ sensor signals (in the ME control unit) sends a so-called sensor counter voltage of approx. 450 mV to the O₂ sensor.

If the O₂ sensor is cold, the sensor internal resistance is so high that the O₂ sensor voltage is initially the same as the back voltage irrespective of the mixture composition.

O ₂ sensor heater

The O₂ sensors are heated in order to rapidly heat up the sensor ceramic to operating temperature. The sensor heater is actuated by the ME control unit through a ground signal. The heater current in the cold state is increased approximately by the factor 4.

The sensor heater is switched off at coolant temperatures below approx. 20°C and at high engine speeds in order to avoid overheating (thermo shock).

If the O₂ sensor is unplugged, the counter voltage at the ME control unit can be measured against the ground of the O₂ sensor signal.

Route of O ₂ sensor signal via multiple signal change (schematic)

Faults at the O₂ sensor can be detected by means of the O₂ sensor signal.

Defined limit values must be maintained for the O₂ sensor voltage, the duration of the period and for the sensor status change.

Fig 6: O2 Sensor Voltage And Time Graph

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

O ₂ sensor signal

Fig 7: O2 Sensor Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The O₂ sensor signal has a steep voltage jump (λ =1) at the transition from a rich to a lean mixture. This property is utilized for the measurements.