2003 Test Groups: 3BMXV02.5M56
WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 2003 BMW Z8, 2003 BMW Z4, 2003 BMW X5, 2003 BMW M5, and 2003 BMW M3. However, it is still accessible from the selected car via links, so may be relevant.
- Heater Diagnosis Of Upstream Wide-Range Oxygen Sensor (General Description) -
Wide range air fuel ratio sensor is ready for operation at a predefined temperature value. In most cases, exhaust gas temperature is not sufficient for heating, and so sensor heating is needed for proper functioning of sensor. Diagnosis consists of 3 checks:
- Operation Readiness - Sensor readiness depends on heater performance. Time delay between "heater on" and operation readiness is monitored. Readiness is checked at defined time ranges (in dependence of engine cooling temperature) after heater has been switched on.
- Temperature Check - A second check is performed continuously. Sensor temperature is expected to remain within a predetermined range, otherwise heater performance is not sufficient and a fault code is set.
- Power Stage Diagnosis - During power stage on and off, control signal (input) of the power stage is compared to its output signal. Also, in switched on condition, heater current is checked against a minimum limit. With these checks, disconnection as well as short to either ground or battery voltage can be detected, and if necessary, fault code can be set. See Fig 1.
- Dynamic Diagnosis (Slow Response) -
Dynamic diagnosis runs at same time as catalyst diagnosis (conversion-efficiency) works. During catalyst and oxygen sensor monitoring, model-based nominal amplitude is modified to higher values. This results into an actual amplitude indicated by signal output of the sensor which is averaged over several lambda cycles (leanest A/F ratio minus richest A/F ratio). To enter into the calculation, each measured value has to be within a predefined confidence interval (window). Fig 2-Fig 3
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Courtesy of BMW OF NORTH AMERICA, INC.
- Plausibility Check - If A/F ratio of upstream sensor is above a predetermined lean value and signal of downstream sensor indicates high voltage, a fault code is set. A/F ratio of upstream sensor is below a predetermined rich value and signal of downstream sensor indicates low voltage, a fault code is set.
- Offset Check - This monitoring looks for incorrect lambda measurement due to shunting effects. If lambda offset of downstream-control exceeds a threshold, a fault code is set.
- Heater Coupling Check - Heater of oxygen sensor is monitored for low impedance coupling between heater and sensor, which can cause lambda modulations with heater pulse rate. If difference of consecutive lambda values exceeds calibration, a fault code is set.
- Monitoring Of Downstream Oxygen Sensors -
The activity of 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, fault code is stored and MIL is illuminated at next driving cycle.
- General Description Of Oxygen Sensor Heater Monitoring - For proper function of the 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 4-Fig 5 .
- Oxygen Sensor Circuit Monitoring (Not Plausible Voltages) -
- 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.
- Oxygen Sensor Circuit Monitoring (Not Plausible Course Of Sensor Voltage) - An open circuit of the sensor upstream catalyst can be detected if voltage is remaining in a specified range after sensor has been heated.