Secondary Air Injection Diagnosis Overview

NOTES:
^ Display groups 020 and 021 are used only for vehicles equipped with a secondary air injection system.
^ Use display groups 020 and 021 to functionally test the secondary air injection system.
^ The functional tests consist of a flow test and a leak test.

FLOW TEST (DISPLAY GROUP 020):
During the flow test, oxygen sensor control is switched OFF (engine is operated in rich condition during this time). At the same time, the secondary air injection pump is switched ON. This means that fresh air is supplied to the exhaust manifold, which increases the oxygen percentage in the exhaust. The oxygen sensor now measures a lean mixture.
To pass the test, the oxygen sensor must measure a lean mixture over a certain time period. This means that the secondary air injection system supplies sufficient air quantity; secondary air injection system OK.

LEAK TEST (DISPLAY GROUP 021):
The prerequisite for this test is to first pass the flow test. With engine warm, the secondary air injection pump is switched ON when the engine is idling. The combination valves however, are not triggered by the secondary air injection valve, instead, they remain closed. When the secondary air injection pump is switched ON, oxygen sensor control of the Engine Control Module (ECM) is observed. If there is no leak in the system, no fresh air can get into the exhaust manifold.
The oxygen sensor control must practically not react (causing a rich or lean condition). On the other hand if this system is leaking, the oxygen sensor control must react to the mixture that is now lean (because of oxygen in the exhaust systm from the secondary air injection system) with definite richening. This definite richening is recognized by the ECM.

METHODS FOR DIAGNOSING THE SECONDARY AIR INJECTION SYSTEM

On-Board Diagnostic Check:
Complete On-Board Diagnostics Check of the system by the ECM with fulfillment of certain diagnostic conditions after each cold start (On-Board Diagnostics).
^ Display the On-Board Diagnostics results using "Read Measuring Value Block" function 08, display groups 020 and 021 at the end of the diagnostic process.
^ Recognized malfunctions are stored in DTC memory.

Shop Diagnosis:
Simplified shop diagnosis option using VAG 1551 scan tool with engine warm:
^ Selective diagnosis using function 04 "Engine basic settings', display groups 020 and 021.
^ Recognized malfunctions are stored in DTC memory.

Evaluating the two diagnostic results:
^ The simplified diagnosis (shop diagnosis) with "Basic Settings" function 04 has only approximate strength of evidence.
^ The results from a complete On-Board Diagnostics check using "Read Measuring Value Block" function 08 have better strength of evidence than a shop diagnosis.
^ If the simplified diagnosis (shop diagnosis) is not passed, there is a malfunction in the secondary air injection system.
^ If the results of the shop diagnosis are OK, but that of the complete On-Board Diagnostics check is not OK, the negative results from the On-Board Diagnostics tests are conclusive; there is a malfunction in the secondary air injection system.