2003 Test Groups: 3BMXV04.4LEV (540i), 3BMXT04.4E53 & 3BMXT04.6XHP
WARNING: This page does not describe the selected car, but rather 18 other vehicles, including the 2002 BMW Z8, 2002 BMW Z3, 2002 BMW X5, 2002 BMW M5, and 2002 BMW M3. However, it is still accessible from the selected car via links, so may be relevant.
- General Description - Response rate of upstream oxygen sensor is monitored by measuring period of lambda control oscillations. See Figure- Figure .
- Diagnosis Procedure Of Downstream Monitor Sensor - Activity of monitor sensor after reaching operating conditions, is determined by 2 different procedures.
- Oscillation Check (Line Crossing) -
- If following checks are correct, monitor sensor will be regarded as okay:
- Monitor sensor signal (sensor voltage) is equal to or greater than nominal value of TV-correction and voltage increases, and if lambda control goes to the lean side, or
- Monitor sensor signal (sensor voltage) is less than the nominal value of TV-correction and voltage decreases, and if lambda control goes to the rich side.
- Fuel Cut-Off Check - In addition to above mentioned checks, signal behavior of monitor sensor is checked in case of fuel cut-off. Therefore, monitor sensor voltage has to be below a given nominal value in case of fuel cut-off. If monitor sensor is detected as defective with oscillation check (line crossing) or fuel cut-off check, a fault code is stored and MIL is illuminated at next driving cycle.
- If following checks are correct, monitor sensor will be regarded as okay:
- Oxygen Sensor Heater Monitoring (Up & Downstream) General Description - For proper function of oxygen sensor, sensor element must be heated. A non-functional heater delays sensor readiness for closed loop control and influences emissions. Monitoring function measures 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 Figure.
- Oxygen Sensor Circuit Monitoring Implausible Voltages
- Voltages exceeding maximum threshold (VMAX) are caused by a short circuit to voltage.
- Voltages falling below minimum threshold (VMIN) are caused by a short circuit of sensor signal or sensor ground to ECM ground. See Figure.
- Implausible Course Of Sensor Voltage - An open circuit of sensor upstream catalyst can be detected if voltage is remaining in a specified range after sensor has been heated.