Secondary Air System Monitoring

Tables of OBD Requirements for Secondary Air System Monitoring

GENERAL DESCRIPTION

At 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)
- no error from the fuel system
- altitude driving conditions below 2448 m (8000 ft)
- no output stage error from the evaporative system
- no error from secondary air pump relay
- 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

- all adaptions of the fuel system are inhibited
- closed loop function of lambda control is inhibited
- the secondary air pump and valve will be switched on
- in case of not reaching the fixed limit by the lambda sensor signal a fault will be detected and stored in the memory
- the diagnosis procedure will be ended and the secondary air system resumes its operating function