Oxygen Sensor: Testing and Inspection
OXYGEN SENSOR MONITORING
General Description
The response rate of the upstream oxygen sensor is monitored by measuring the period of the lambda control oscillations. This measurement is performed under the following conditions.
manual transmission automatic transmission
engine speed: 1,400 - 2,600 rpm and 1,200 - 2,200 rpm
load: 0.7 [<] IL [<] 1.9 ms and 0.7 [<] TL [<]2.2 ms
(catalyst temperature is[>] 352 °C)
Monitoring Structure
Oxygen Sensor Monitoring
Monitoring of electrical faults of sensors upstream and downstream of catalyst:
Implausible voltages
- ADC-voltages exceeding the maximum threshold UMAX are caused by a short circuit to Ubat
- ADC-voltages falling below the minimum threshold UMIN are caused by short circuit of sensor signal or sensor ground to EMC ground
Implausible course of sensor voltage
A 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.
Flow chart of monitoring function (oxygen sensor)
Oxygen Sensor Heater Monitoring
For proper function of the 02-sensor, the sensor element must be heated. A none functioning heater delays the sensor's readiness for closed loop control and thus influences emissions.
The monitoring function measures both, the sensor heater current (voltage drop across a shunt) and the heater voltage (heater supply voltage) to calculate the sensor-heater resistance.
The monitoring function is activated continuously, if the heater has been stabilized, and the current falls to a static value
Therefore the resistance of the 02-sensor heaters, with the help of a shunt both before and after the catalyst are measured and an additional right/left diagnosis is realized.
Circuitry for heater controlling and heater current measuring
characteristics:
- ECM-controlled switching on of sensor heater
- One shunt for each 02-sensor pair upstream and downstream of catalysts: for current measuring
Flow chart of monitoring function (oxygen sensor heater)
