Component description for a O2 sensor - GF07.04-P-6100BK
ENGINE 113.967 in MODEL 219
ENGINE 113.964 in MODEL 164.1
ENGINE 113.971 in MODEL 251
Shows model 219
Location
The O2 sensors are located in the front part of the exhaust system as follows:
- Model 219 in front and after the firewall catalytic converter
- Models 164.1, 251 in front of to the side on the catalytic converter (exhaust system without underfloor catalytic converters).
Connector for O 2 sensors in a round and angular version (View of connector on O 2 sensor)
Task
The O2 sensors detect the residual oxygen share in the exhaust and transmit corresponding voltage signals to the ME control unit.
The following functions are dependent on the O sensor signals:
O 2 sensor signal from O 2 sensors upstream TWC (control sensors)
- Closed-loop mixture control
- Self-adaptation of mixture formation
- Function chain tests.
O 2 sensor signal from O 2 sensors downstream TWC (guide or diagnosis sensors)
- Two-sensor control
- Monitoring catalytic converter effect
Functional principle
Design
The sensors used are potential-free insulated O2 planar sensors.
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. The ground cable for the sensor signal for each O2 sensor is routed individually up to the ME control unit.
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 gives the O2 sensor signal, which is a measurement for the residual oxygen content in the exhaust gas.
The evaluation circuit of the O2 sensor signal (in the ME control unit) gives a so-called 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 warm up the sensor ceramic rapidly 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 (thermal shock).
if the O2
sensor is unplugged, the counter voltage at the ME control unit can be measured against the O sensor signal ground.
O 2 sensor signal travels via several signal changes (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.
sensor signal
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 lambda closed-loop control.