Air Injection: Testing and Inspection

Secondary Air System Monitoring

Function Modules:







Principle of algorithm:
1. Evaluation during active secondary air injection (=SAI):
- Calculation of nominal secondary air mass depending on battery voltage, altitude factor, exhaust pressure.

- Calculation of lambda(exhaust) nominal depending on secondary air dilution factor and required engine enrichment lambda(engine):
Lambda(exhaust) = (1 + m(SAI, nominal) / m(air, HFM)) * lambda(engine)

- Two-step lambda control activated for actual lambda(exhaust) signal from lambda sensor < 1 (rich mixture in exhaust gas => defective SAI)

- Calculation of m(SAI, actual) from two-step lambda control (fr = lambda correction factor):
m(SAI, actual) = fr * m(air, HFM) - m(air,HFM)
(with fr not equal to 1)

(fr: multiplicative factor - closed loop regulator)

2. Evaluation after deactivation of SAI:
- Check of pilot control and reject result, if threshold exceeded.

3. Fault evaluation:
- Fault detection after comparison of the quotient of secondary air mass flow to fault threshold.

Active Monitors
The monitor of the secondary air injection system (SAI) is a functional check to detect
- a failure of the secondary air pump or
- a blocking or leaking between secondary air pump and exhaust manifold.

The SAI monitor only includes an active check. The check is performed with the following monitoring conditions.

The active SAI monitor is performed mainly during engine idle. The SAI monitor observes the calculated secondary air mass flow. If this value is above a threshold the SAI will work properly.

Monitoring conditions for active check:
- engine coolant temperature in between calibrated thresholds,
- Intake air temperature in between calibrated thresholds,
- modeled catalyst temperature < calibration
- altitude correction for fuel injection > calibration,
- lambda control ready for operation,

- no exclusion due to request of other functions:
- e.g. no monitoring of mixture system, canister purge valve,
- e.g. no activity of mixture system and canister purge valve
- e.g. no faults of engine coolant temperature sensor, mass air flow sensor,
intake air temperature sensor, SAI power stage, leak detection system, canister purge valve power stage, oxygen sensor(s) pre-catalyst, misfire, battery voltage.

Diagnosis of Secondary Air System - Active SAI Monitor