2003 Test Groups: 3BMXV03.0LER, 3BMXV03.0M5R & 3BMXT03.0E5R

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Monitoring Structure & General Description - Both oxygen sensors upstream from the catalyst are separately monitored for rich and lean voltage and response time (period monitoring and jump period monitoring). See Fig 1.

Fig 1: Oxygen Sensor Monitoring
Courtesy of BMW OF NORTH AMERICA, INC.
Upstream Oxygen Sensor Monitoring Procedure - To determine switching time, lean and rich period times are added during a fixed number of lambda controller cycles. A malfunction is registered if one or both of the times exceed the thresholds which depend on engine speed and load. See Fig 2.

Fig 2: Flow Chart Of Monitoring Oxygen Sensor Switching Time (Lean To Rich)
Courtesy of BMW OF NORTH AMERICA, INC.
Monitoring Of Downstream Oxygen Sensors - The activity of the monitor sensor after reaching operating conditions, is determined by an oscillation check of sensor signal (voltage). If conditions of following checks are fulfilled, monitor sensor is regarded to be in order:
- Monitor sensor signal (sensor voltage) is greater or equal than a predetermined value at normal engine operating condition (normal combustion).
- Sensor voltage drops below a predetermined value during fuel cut-off conditions. If monitor sensor has detected a defect, a fault code is stored and MIL is illuminated at next driving cycle.
General Description Of 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 continuously both sensor heater current as well as heater voltage (heater supply voltage) to calculate sensor heater resistance. See Fig 3-Fig 4 .

Fig 3: Heater Control & Heater Current Circuit
Courtesy of BMW OF NORTH AMERICA, INC.

Fig 4: Oxygen Sensor Heater Monitoring Flow Chart
Courtesy of BMW OF NORTH AMERICA, INC.
Oxygen Sensor Circuit Monitoring - Electrical faults in oxygen sensor circuit sensors upstream and downstream of catalyst are monitored. If implausible voltages are detected:
- Voltages exceeding maximum threshold are caused by a short circuit to voltage.
- Voltages falling below minimum threshold are caused by a short circuit of sensor signal or sensor ground to PCM ground.
If not plausible course of sensor voltage is detected, an open circuit of sensor upstream can be detected, if ADC voltage is remaining in a specified range after sensor has been heated.