Component description for a O2 sensor - GF07.04-P-6100AMH

ENGINE 156.980 in MODEL 164, 251 up to Model Year 8

O2 sensors for CAT

ENGINE 156.982 in MODEL 209

O2 sensors for CAT

ENGINE 156.983 in MODEL 211, 219

O2 sensors for CAT

ENGINE 156.984 in MODEL 216, 221 up to Model Year 8

O2 sensors for CAT

Location (voltage-jump oxygen sensors) for model 164, 216, 221, 251

The O ₂ sensors downstream of TWC are screwed into the middle of the firewall catalytic converter.

Fig 1: Identifying Firewall Catalytic Converter And Left/Right O2 Sensor

Courtesy of MERCEDES-BENZ USA

Location (voltage-jump oxygen sensors) for model 209, 211, 219

The O ₂ sensors downstream of TWC are screwed in behind the firewall catalytic converter.

Fig 2: Identifying Firewall Catalytic Converter And Left/Right O2 Sensor

Courtesy of MERCEDES-BENZ USA

Task

The O ₂ sensors downstream of TWC (guide and diagnostic sensors) detect the residual oxygen content in exhaust gas for the following tasks:

Two-sensor control
Monitoring catalytic converter efficiency

Design

The O ₂ sensors downstream of TWC are insulated as voltage free and designed as a planar (flat) wideband oxygen sensors.

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

Fig 3: Identifying Design Of O2 Sensors Downstream Of TWC

Courtesy of MERCEDES-BENZ USA

Connector

Fig 4: Identifying Sensor Heater Voltage, Sensor Heating Ground, Ground Signal Voltage And Signal Voltage

Courtesy of MERCEDES-BENZ USA

Function (schematic)

Fig 5: Identifying O2 Sensors Downstream Function Diagram

Courtesy of MERCEDES-BENZ USA

Signal voltage

The signal voltage has a steep voltage jump ( =1) at the transition from a rich to a lean mixture. This property is utilized for lambda closed-loop control.

Fig 6: Identifying O2 Sensors Signal Voltage Graph

Courtesy of MERCEDES-BENZ USA

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 boundary surfaces as a result of particular properties of the sensor ceramic (Nernst voltage). This voltage (signal voltage) is the measure for the residual oxygen content in the exhaust.

The electronics in the ME-SFI [ME] control unit (N3/10) produce a so-called sensor back voltage of about ca. 450 mV at the voltage-jump oxygen sensor. For the voltage-jump oxygen sensor, the internal resistance of the sensor is so high that the sensor voltage is initially equal to the back voltage irrespective of the mixture composition (λ).

The sensor back voltage at the ME-SFI [ME] control unit can be measured to the sensor ground if the voltage-jump oxygen sensor is disconnected.

sensor heating

In order to bring ceramic probe bodies quickly up to operating temperature the voltage-jump oxygen sensors are heated constantly with a heat output of about 7 W. The sensor heaters are actuated by the ME-SFI [ME] control unit by means of a ground signal. The heater current in the cold state is increased approximately by a factor of 4.

At coolant temperatures greater than about 20°C and at high engine speeds, the sensor heaters are switched off to prevent overheating (thermal shock).