Secondary Air System Monitoring
GENERAL DESCRIPTIONAt cold start the secondary air pump and valve are switched on for their normal operating function. The secondary air delivered into the exhaust gas is causing an increase of the lambda sensor signal until it reaches a predetermined value. This fixed limit corresponds to the minimum amount of secondary air (low-flow-limit-check).
MONITORING STRUCTURE
1. Check conditions
To start the diagnosis function several conditions have to be satisfied:
- secondary air system is on
- no error from coolant temperature sensor
- lambda sensor is heated up (stabilized condition)
- altitude driving conditions below 2448 m (8000 ft)
- no error from the evaporative system
- no error from secondary air pump output stage
- no error from the battery voltage
- no error from the air mass sensor
- no error from the plausibility check of throttle valve and air mass sensor
- closed evaporative system purge valve
Furthermore if the diagnosis has already been started and one of the conditions has not been satisfied continuously, the process will be interrupted.
2. Check procedure
- check conditions true
- start of monitoring procedure
- looking at the signal of the lambda sensor before the catalyst
Signal below threshold for definite times:
System is i.o., cycle byte is set and end of the monitoring procedure
Signal above threshold for definite times:
store secondary air system fault and set cycle byte. If the fault is confirmed during the next driving cycle, the MIL is illuminated