Rear Oxygen Sensor
The wiring to the oxygen sensors must not be squeezed or in any other way damaged. It is also not allowed to grease the contacts for the oxygen sensors as the oil in the grease would interfere with the reference air and the function of the oxygen sensors. Even the area where the cable harness connects to the oxygen sensor body must be protected from contamination for the same reason.
The rear oxygen sensor is used to give Engine Control Module (ECM) information about remaining oxygen content in the exhausts behind the catalytic converter. The information is used by Engine Control Module (ECM) to check the catalytic converter's function. This check is performed when conditions for catalytic converter diagnosis are fulfilled.
The rear oxygen sensor has a fine tuning and barely measurable effect on the regulation of the mixing ratio of air and fuel. The Engine Control Module (ECM) uses the signal to optimize the signal from the front oxygen sensor.
The oxygen sensor uses voltage control. The signal characteristic is binary. With a binary signal characteristic, the amplitude of the signal curve changes considerably when changing the oxygen content in the exhaust gases. Otherwise its components and function are the same as the front oxygen sensor, see FRONT OXYGEN SENSOR .
Preheating element
The normal operating temperature is between 300-900 °C. It does not work below 300 °C. The oxygen sensors are electrically pre-heated so that operating temperature is rapidly reached. Heating also ensures that the oxygen sensors maintain a normal operating temperature and to prevent condensation which could damage the oxygen sensor.
The oxygen sensor's heating coil consists of a PTC-resistor. The heating coil is supplied with voltage from the system relay and is grounded internally in the Engine Control Module (ECM).
In order to avoid condensation damage to the oxygen sensor, current is initially pulsated from the Engine Control Module (ECM). Depending on temperature, regard is given to the temperature in the dew and as the temperature in the PTC resistor increases, the resistance in the resistor increases, the current is reduced and gradually transferred to a non-pulsated current
The heating period for the rear oxygen sensor is short, approx.60 - 120 seconds.
The oxygen sensor, including heating element, can be diagnosed by the Engine Control Module (ECM), and signals from the oxygen sensor can be read out.