GF07.04-P-6104MLK Component Description For A O2 Sensor Upstream of CAT

GF07.04-P-6104MLK Component Description For A O2 Sensor Upstream Of CAT
- refinement package
- as of model year 09

Component Identification:

Location
The O2 sensors upstream of CAT are screwed into the exhaust pipes upstream of the firewall catalytic converters.

Task
The O2 sensors upstream of CAT (control sensors) detect the residual oxygen content in exhaust gas for the following tasks:
- Lambda control
- Self-adjustment of mixture formation
- Function chain tests (for on-board diagnosis (OBD))

Design

Component Identification:

The O2 sensor downstream of CAT is designed as an insulated potential-free and planar (flat) voltage-jump oxygen sensor.
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.

Component Identification:

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 signal voltage is produced at boundary surfaces as a result of particular properties of the sensor ceramic (Nernst voltage). This 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 a cold 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 (Lamda).

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

Oxygen sensor heater
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 oxygen sensor heaters are actuated with a ground signal from the ME-SFI control unit.

At coolant temperatures under 20 °C and at high engine speeds, the oxygen sensor heaters are switched off to prevent damage (by thermal shock).

Power is supplied to the oxygen sensor heaters through "circuit 87 M2".

Component Identification:

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