Secondary Air System Monitoring

SECONDARY AIR SYSTEM MONITORING

GENERAL DESCRIPTION

Passive check (without Lambda control): During the natural secondary air phase after cold start the Secondary Air Monitoring is conducted by evaluating the voltage of the two upstream oxygen sensors. The check will determine if the sensor voltage is below a certain threshold during a defined period of time, and if this is an indication of proper function of the secondary air system.

Active check (with Lambda control ): This additional check, at idle with active Lambda control, will be conducted only if the Passive Check diagnosis was not completed during warm-up.

A) Passive check







1. Check conditions
To start the diagnosis function several conditions have to be satisfied:
- secondary air system is on
- oxygen sensors are hot and on-line
- engine temperature after coldstart[>] 30 °C
- elevation [<] approximately 2,448 m
- 680 rpm engine speed [<] 2,800 rpm
- 0.7 ms engine load [<] 3.0 ms
- air mass flow [<] 100 kg/h
- time after start: [>] 50 sec

If the diagnosis has begun and one of the conditions has not been satisfied continuously the check will be interrupted.

2. Check procedure
Because of the fact that the Secondary Air Monitoring is operating during the natural secondary air phase after cold start, no other functions need be inhibited.
- Secondary air pump and valve are switched on immediately after cold start ( engine start temperature must be lower than 45 °C).
- Start of the Secondary Air Monitoring begins after reaching the above mentioned conditions.
- In case the lambda sensor signal has not reached the fixed limit, a fault will be detected and stored in memory.

B) Active check
If the Passive Check diagnosis could not be completed an additional Active Check will be performed. For testing the air injection pump will be switched on and due to the excess of oxygen in the exhaust gas the lambda control switches rich After exceeding a certain limit the check is successfully completed.







1. Check conditions
To start the diagnosis function several conditions have to be satisfied:
- no check completed per procedure A)
- engine at idle
- vehicle speed = 0
- elevation [<] approximately 2,448 m
- engine temperature [<] 95 °C
- intake air temperature [>] -11 °C
- Lambda control active

It the diagnosis has begun and one of the conditions has not been satisfied continuously the process will be interrupted.

2. Check procedure
If the start conditions are as above the fuel tank ventilation will be interrupted and the air injection pump will be switched on.
- storing of the actual Lambda value ( FRSLSA)
- observing the actual Lambda value
- if Lambda value (FR) [>]= FRSLSA + DFRSLP --> Check o.k.
switch off air injection pump

- FR [<] FRSLA + DFRSLP + t [>] TDSLP --> Check not o.k.
store fault. switch off air injection pump

FR = Lambda value
FRSLSA = actual Lambda value
DFRSLP = threshold (change of lambda control)
TDSLP = maximum check time
t=time