Oxygen Sensor Monitoring

MONITORING STRUCTURE

GENERAL DESCRIPTION

The response rate of up the stream oxygen sensor is monitored by measuring the period of the lambda control oscillations.





Flow Chart of Monitoring Function

Oxygen Sensor Heater Monitoring

For proper function of the oxygen sensor, the sensor element must be 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.





Circuitry for heater controlling and heater current measuring

Characteristics:
- ECM - controlled switching on of the sensor heater
- one shunt for each sensor heater upstream and downstream of catalyst for current measurement





Flow Chart of Monitoring Function

Oxygen Sensor Circuit Monitoring

Monitoring of electrical faults of sensors upstream and downstream of catalyst

Unplausible voltages
- ADC - voltages exceeding the maximum threshold VMAX are caused by a short circuit to VBatt
- 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 is remaining in a specified range after the sensor has been heated