Secondary Air System Monitoring
.05.00.00 Secondary Air System Monitoring
.05.01.00 Via Lambda Deviation
.05.01.01 General Description
After cold start condition (e.g. 5 .. 40 degrees C) the Air system blows for a certain time air into the exhaust manifold. The exhaust gases will be enriched with oxygen and post combustion of HC and CO occurs. By this exothermic reaction the exhaust system will be heated and the time to reach the lightoff temperature of the catalyst will be accelerated.
Principal sketch and main components of Air System: (example 4 cyl. Engine)
ECM;
Air pump relay
Air valve (solenoid valve)
Air valve (vacuum controlled)
AIR pump;
O2 Sensor;
.05.01.02 Monitoring Structure
The following table shows an overview of the used function and monitor strategy for all test groups:
The monitor of the secondary air system distinguish between two functions:
a) Passive monitoring function will be carried out during normal secondary air injection While engine is cold started and
b) Active monitoring function will be activated later during the driving cycle, if the passive Monitoring function has not a pass result.
At idle state or under part load engine condition, the secondary air pump is switched on and the valve opens either by pressure of the pump or vacuum operated by switching to open, causing an increase in the air fuel ratio. The Oxygen Sensor control function (closed loop) enriches the mixture consisting of exhaust gas of the engine and secondary air until the Lambda integrator signal will meet a predetermined value (functional or flow check).
Check Conditions
Passive Monitoring Function
To start the passive monitoring function, following conditions have to be satisfied:
Oxygen sensor readiness
No engine restart (thermal energy introduced)
A certain time after engine start
Engine has been cold started
No output stage error from secondary air pump relay
Active Monitoring Function
To start the active monitoring function several conditions have to be satisfied:
No result or no pass result from passive monitoring function available.
Engine running at idle
Closed loop condition of the Lambda-control
Monitoring function not done before (for pump protection)
No output stage error from secondary air pump relay
Furthermore, if the diagnosis has already been started and one of the conditions has not been satisfied continuously, the process will be interrupted.
The following conditions have to be fulfilled additionally:
All adaptations of the air/fuel system are inhibited
The Lambda controller has been stabilized (waiting for several transients of the oxygen sensor signal)
The actual Lambda controller value has been stored
In case of an interrupt of diagnosis, the monitor can several time started again (different for each test group; see overview) during the same driving cycle if the monitor conditions are met.
.05.01.03 Chart(s) and flow chart(s)
Following charts shows the phases of the AIR monitoring via lambda deviation for passive and active monitoring.
AIR system monitoring
DTC's See summary table
Sensors OK ECTS, Front O2S
Secondary Parameter See summary table
Monitor execution Passive check during normal operation
Threshold Malfunction criteria from summary table as relation
between actual and expected AIR.
.05.02.00 Via exhaust temperature sensor
.05.02.01 General Description
After cold start condition (e.g. 5 .. 40 degrees C) the Air system blows for a certain time air into the exhaust manifold. The exhaust gases will be enriched with oxygen and post combustion of HC and CO occurs. By this exothermic reaction the exhaust system will be heated and the time to reach the lightoff temperature of the catalyst will be accelerated.
Additional to the principal sketch above, those systems using an exhaust temperature sensor as an indicator of AIR mass.
.05.02.02 Monitor function description
Passive monitoring function
During normal secondary air injection the secondary air is indirect monitored via exhaust temperature using an exhaust temperature sensor. The measured exhaust temperature will be compared with modeled target temperatures contained in a map within ECM. After the secondary air injection ECM is calculating the amount of introduced thermal energy additionally. As long as the temperature sensor shows an increase in exhaust gas temperature and the thermal energy introduced (calculated by air mass times injected fuel), the secondary system will pass the monitor. No further active diagnostic will be performed.
If one of the expected conditions fails, e.g. the temperature sensor is not showing an increase of temperature or the thermal energy introduction is below an expected threshold, the active monitoring function will be carried out later in that driving cycle.
AIR System monitoring (via exhaust temperature sensor)
DTC's See summary table
Sensors OK ECTS, Front O2S
Secondary Parameter See summary table
Monitor execution Passive check during normal operation
Threshold Decision criteria for pass condition from summary table as relation
between actual and expected AIR.
.05.02.03 Chart(s) and flow chart(s)
