Repair manual

SULEV 2.0L TFSI Engine

Testing the System

The California Air Resources Board (CARB) requires that

the secondary air system be monitored during the heat-

up phase of the catalytic converter.

Previously, the system was monitored using the oxygen

sensor. However, this downstream sensor does not

become available quickly enough. For this reason, the

system is monitored and evaluated for pressure-based

secondary air diagnosis by Secondary Air Injection Sensor

1 G609.

Pressure-Based Secondary Air Diagnosis

Process

Phase 0

The control module initialization process begins at

“ignition on.” The signal from Secondary Air Injection

Sensor 1 G609 is stored and compared to the signals

received from the ambient pressure sensor and the intake

manifold pressure sensor.

Phase 1

When the secondary air mass is injected, the pressure

within the secondary air system also rises to above

atmospheric pressure. This pressure increase is

determined by G609. The resulting analog signal is

evaluated by the ECM. If the signal exceeds the pre-

deﬁned limit, for example due to a blockage in the

system or leakage, a DTC entry will be generated. Engine

Electronics Indicator Lamp K149 will also be activated. If

the system is still in order, the diagnosis procedure will

be continued.

Phase 2

During this phase, Secondary Air Injection Valve N112 is

closed and checked for leaks. The value determined by

Secondary Air Injection Sensor 1 G609 is evaluated for

this purpose.

Phase 3

The secondary air pump is shut OFF and Secondary Air

Injection Valve N112 closed. The difference between the

actual measured pressure and the stored value generated

in phase 0 is evaluated.

A faulty Secondary Air Injection Pump (pump does not

shut off) or a faulty Secondary Air Injection Sensor 1 G609

can thus be detected.

Reference

On the next page you will ﬁnd a diagram

showing the individual phases of the

secondary air diagnosis process.