Test Group YBMXV04.9S62

Monitoring Upstream Oxygen Sensor 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 Figure.

Monitoring Procedure Of Upstream Oxygen Sensor 

1. Overall Period Time Monitoring Of Upstream Oxygen Sensor -  For determining the 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(s) the thresholds which depends on engine speed and load. See Fig 1 and Fig 2 .
2. Monitoring Procedure of Downstream Oxygen Sensors - 
   • Monitoring From Rich To Lean Intake Mixture -  The lean sensor voltage is used for diagnosis of the sensors activity. Therefore this check is performed during deceleration fuel cut-off. The diagnosis starts after a calculated air mass (integral) is reached at transient from any operation mode to the fuel cut-off mode and a defined time in deceleration fuel cut-off. Sensor voltage has to drop below a predetermined value otherwise a fault is detected and a code is stored.
   • Monitoring From Lean To Rich Intake Mixture -  When the diagnosis conditions at deceleration fuel cut-off are not fulfilled, the diagnosis is carried out in opposite direction of the oxygen sensor voltage. For a positive diagnosis result the signal must overrun a threshold after deceleration fuel cut-off. To ensure the diagnosis, the mixture can be short-term enriched independent of the respective operating conditions.
3. Oxygen Sensor Heater Monitoring General Description -  For proper function of the oxygen sensor, the sensor element must be heated. A non functioning heater delays sensor readiness for closed loop control operation and influences emissions. The monitoring function measures continuously both, sensor heater current as well as heater voltage (heater supply voltage) to calculate sensor heater resistance.
   • Circuitry For Heater Controlling & Heater Current Measuring -  See Fig 3.
   • Flow Chart Of Oxygen Sensor Heater Monitoring -  See Fig 4.
4. Oxygen Sensor Circuit Monitoring -  Monitoring of electrical faults of sensors upstream and downstream of catalyst takes as follows:
   • Not Plausible Voltages - 
     1. ADC voltages exceeding the maximum threshold VMAX are caused by a short circuit to battery voltage.
     2. ADC voltages falling below minimum threshold VMIN are caused by a short circuit of sensor signal or sensor ground to ECM ground.
   • Not Plausible Course Of Sensor Voltage - 
     1. An open circuit of the sensor upstream catalyst can be detected, if the ADC voltage is remaining in a specified range after the sensor has been heated.

Fig 1: Overall Period Time Monitoring Of Upstream Oxygen Sensor

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Jump Period Monitoring Of Upstream Oxygen Sensor

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 3: Circuitry For Heater Controlling & Heater Current Measuring

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 4: Flow Chart Of Oxygen Sensor Heater Monitoring

Courtesy of BMW OF NORTH AMERICA, INC.