Oxygen Sensor Monitoring
Monitoring of Upstream Oxygen SensorsGeneral Description of Upstream Oxygen Sensor Monitoring
Both oxygen sensors upstream from the catalyst are separately monitored for rich and lean voltage and response time (period monitoring and jump period monitoring).
Upstream Oxygen Sensor Monitoring Procedure
To determine the switching time the lean and rich period times are added during a fixed number of lambda controller cycles.
A malfunction is registered if one or both of the times exceed(s) the thresholds which depend on engine speed and load.
Flow Chart of Monitoring Oxygen Sensor Switching Time (lean to rich)
Monitoring of Downstream Oxygen Sensors
The activity of the monitor sensor after reaching operating conditions, is determined by an Oscillation Check of the sensor signal (voltage).
If the conditions of following checks are fulfilled the monitor sensor is regarded to be in order:
The monitor sensor signal (sensor voltage) is greater or equal than a predetermined value at normal engine operating condition (normal combustion)
or
The sensor voltage drops below a predetermined value during fuel cut-off conditions.
If the monitor sensor is detected defect in this Checks, a fault code is stored and the MIL is illuminated at the next driving cycle.
Oxygen Sensor Heater Monitoring
General Description of 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 continuously both, the sensor heater current as well as the heater voltage (heater supply voltage) to calculate the sensor heater resistance.
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 Oxygen Sensor Heater Monitoring
Oxygen Sensor Circuit Monitoring
Monitoring of electrical faults of sensors upstream and downstream of catalyst
Not plausible 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
Not plausible 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