Oxygen Sensors
Oxygen Sensors:Due to the compact exhaust system used on the M52 Z3 the number of oxygen sensors used in the exhaust system has been reduced by two (one pre and one post sensor used).
Stereo oxygen sensor monitoring is not utilized in the Z3 for mixture control.
The "resistive jump" sensors are the same type used in the 328i.
A voltage drop to ground occurs at the sensor probe based on the oxygen content in the exhaust gas.
The MS41.1 oxygen sensors function differently from the familiar Bosch type sensors. However, the end result of the O2 feedback system is the same. The control module uses the signals from the sensors to maintain LAMBDA = 1.
The MS 41.1 oxygen sensors are called "Resistive - Jump" sensors.
The probe of the sensor which is exposed to the exhaust gasses is made from titanium dioxide [TiO2] (a semi-conductive material.) When heated to an operating temperature of 600° to 700°C, the titanium dioxide becomes conductive and will allow current to flow, based on the amount of oxygen in the exhaust.
The resistance value of the sensor changes rapidly when the mixture deviates from Lambda = 1. If the oxygen content in the exhaust is high (LEAN MIXTURE), the oxygen molecules will block the flow of electrons through the titanium dioxide. This creates high resistance, or a small voltage drop across the sensor tip.
As the oxygen content in the exhaust drops (RICH MIXTURE), the resistance to electron flow drops and the semiconductive tip allows electron flow, creating a large voltage drop across the sensor.
Two catalysts are employed for exhaust gas conversion along with two additional O2 sensors mounted at the rear of each converter.
The rear sensors are used for OBD II compliance. The rear sensors monitor the efficiency of the catalyst by measuring the oxygen content in the exhaust after the conversion.
The MS 41.1 control module supplies the O2 sensor with a standing voltage of five volts. The module then monitors the voltage drop across the sensor tip as its measure of lambda swing. The voltage signal at the control module will switch between approximately 4.6 to 0.1 volts as the mixture changes from lean to rich either side of Lambda = 1.
Operation of the sensors is monitored as part of the OBD II requirements. The pre-catalyst sensors are monitored for the following:
- Response Time
- Voltage fluctuation
- Switching Time
- Heater Operation
The post-catalyst sensors are monitored for:
- Voltage fluctuation
- Heater Operation
Failure of a sensor in any area of monitoring will cause the Check Engine Lamp to illuminate and the fault will be stored in memory.