Test Group WBMXV01.9M44

General Description -  Response rate of upstream oxygen sensor is monitored by measuring period of lambda control oscillations. See Fig 1.

Oxygen Sensor Heater Monitoring -  For proper function of oxygen sensor, sensor element must be heated. A non-functioning heater delays sensor readiness for closed loop control and influences emissions. Monitoring function measures both sensor heater current (voltage drop over a shunt), and heater voltage (heater supply voltage) to calculate sensor heater resistance. Monitoring function is activated once per trip if heater has been switched on for a certain time period and current has stabilized. See Fig 2-Fig 3 .

Oxygen Sensor Circuit Monitoring -  Oxygen sensor circuit monitors electrical faults of sensors upstream and downstream of catalyst. Implausible voltages are voltages exceeding maximum threshold (VMAX). Voltages falling below minimum threshold (VMIN) are caused by a short circuit of sensor signal or sensor ground to ECM ground. An open circuit of sensor upstream catalyst can be detected if voltage is remaining in a specified range after sensor has been heated. See Fig 4.

Fig 1: Oxygen Sensor Monitoring Structure

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Flow Chart Of Monitoring Function

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 3: Flow Chart Of Oxygen Sensor Monitoring Function

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 4: Circuitry For Heater Controlling & Heater Current

Courtesy of BMW OF NORTH AMERICA, INC.