BMW 11781247406 Oxygen Sensor - Front

Both OBO I and OBO II systems utilize an Oxygen (02) sensor upstream from the catalytic converter to monitor the fuel mixture. OBO II systems also have a Heated Oxygen (H02) sensor located before and after the catalytic converter. The advantage of the H02 sensor is its ability to reach operating temperature quickly, allowing the Engine Control Module (ECM) to control fuel injection more efficiently and reduce emissions. The post catalytic converter H02 sensor is used to monitor the pre catalytic converter H02 sensor. These sensors compare the oxygen content of outside air with the oxygen content in the exhaust gases and generate a voltage signal for the ECM. The voltage signal ranges from 0.6 to 0.9 volts for a rich mixture and 0.0 to 0.3 volts for a lean mixture. Fluctuations in voltage occur during the transition from rich to lean or lean to rich. If the voltage fails to fluctuate or the sensor response is slow, potential causes include blocked sensor tip openings, thermal overload, silicone contamination, fuel contamination, improper electrical terminal resistance, inoperative oxygen sensor heater, ECM control switch off, or damage from electrical contact cleaner. To test the sensors, a BMW service tester or suitable Data Scan Tool can be used, or a digital volt/ohmmeter can be used to check component values. The 02 sensor voltage should continuously fluctuate between 0.1-9 volts for Bosch sensors and 0.1-4.9 volts for Siemens sensors. To check the sensor response to lean or rich mixtures, create an air leak or increase fuel pressure respectively. To test the Bosch HO2/02 sensor, allow the engine to reach normal operating temperature, raise the vehicle, and probe pin Nos. 1 and 2 of the sensor's electrical connector with a digital volt meter. The voltage should fluctuate within a couple of minutes. If not, check the sensor heating circuit or replace the sensor if it lacks a heater circuit. For vehicles with Heated Oxygen sensors, check the heater circuit and element by measuring resistance and checking for battery voltage between terminal Nos. 3 and 4. If necessary, replace the sensor or check the wiring and heater relay. When removing and installing the Oxygen sensor, avoid using sealants containing silicone in the intake area as it can damage the sensor. Additionally, avoid using electrical contact cleaner near the H02 sensor harness electrical connector to prevent corrosion damage.