Test Group 1BMXV05.4LEV
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- The response rate of the upstream oxygen sensor is monitored by measuring the period of the lambda control oscillations. See Figure-Figure
. For diagnosis procedure of monitor sensor (downstream), 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.
- The monitor sensor signal (sensor voltage) is greater than or equal to the nominal value of the TV correction and voltage increases, or if lambda control goes to the lean side.
- Monitor sensor signal (sensor voltage) is less than nominal value of TV correction and voltage decreases, or 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 defective by OSCILLATION CHECK or FUEL CUT-OFF CHECK, a fault code is stored and MIL is illuminated at next driving cycle.
- Oscillation Check (Line Crossing) -
If following checks are correct, monitor sensor will be regarded as okay.
- Oxygen Sensor Heater Monitoring (Up/Downstream) - 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 and current has stabilized. See Fig 1-Fig 2 .
- Oxygen Sensor Circuit Monitoring - Monitoring of electrical faults of sensors upstream and downstream of catalyst. Implausible voltages are voltages exceeding the maximum threshold and 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 ECM ground. Implausible cause of sensor voltage is an open circuit if sensor upstream catalyst can be detected, or if voltage remains in a specified range after sensor has been heated.