Test Group YBMXT04.4E53, YBMXT04.453M, YBMXV04.4LEV & YBMXV05.4LEV
Oxygen Sensor Monitoring General Description - The response rate of the upstream oxygen sensor is monitored by measuring the period of the lambda control oscillations. See Fig 1 - Fig 2 .
- Diagnosis Procedure Of The Monitor (Downstream Sensor) -
The activity of the monitor sensor after reaching operating conditions, is determined by the 2 different procedures that follow:
- Oscillation Check (Line Crossing) -
If the following checks are correct, the monitor sensor will be regarded as okay:
- The monitor sensor signal (sensor voltage) is greater than or equal to than the nominal value of the TV-Correction and voltage increases, if the lambda-control goes to the lean side.
- The monitor sensor signal (sensor voltage) is less than the nominal value of the TV-Correction and voltage decreases, if the lambda-control goes to the rich side.
- Fuel Cut-Off Check -
Additionally to the above mentioned checks, the signal behavior of the monitor sensor is checked in case of fuel cut-off. Therefore the monitor sensor voltage has to be below a given nominal value in case of fuel cut-off.
If the monitor sensor detects defects with the checks A or B, a fault code is stored and the MIL is illuminated at the next driving cycle.
- Oscillation Check (Line Crossing) -
If the following checks are correct, the monitor sensor will be regarded as okay:
- Oxygen Sensor Heater Monitoring (Up & Downstream Sensors) - For proper function of the oxygen sensor, the sensor element must heated. A non-functioning heater delays the sensor readiness for closed loop control and influences emissions. The monitoring function measures both, sensor heater current (voltage drop over a shunt) and the heater voltage (heater supply voltage) to calculate the sensor heater resistance. The monitoring function is activated once per trip, if the heater has been switched on for a certain time period and the current has stabilized. See Fig 3.
- Flow Chart Of Oxygen Sensor Heater Monitoring Function - See Fig 4.
- Oxygen Sensor Circuit Monitoring -
Monitoring of electrical faults of sensors upstream and downstream of catalyst, consists of following:
- Unplausible Voltages - ADC voltages exceeding the maximum threshold VMAX are caused by a short circuit to battery voltage, or ADC voltages falling below the minimum threshold VMIN are caused by a short circuit of sensor signal or sensor ground to ECM ground.
- Unplausible Course Of Sensor Voltage - An open circuit of the sensor upstream catalyst can be detected, if the ADC voltage remains in a specified range after the sensor has been heated.