Display Group 020 & 021
NOTE:- Display groups 020 and 021 are only considered in vehicles with secondary air injection system.
- If in display group 029, display field 1, the value of the secondary air injection system flow and leak test is not set to "0" when the readiness code is regenerated and/or there is a malfunction in the DTC memory that relates to the secondary air injection system, display groups 020 and 021 are used for selective diagnosis.
Function testing consists of one flow and one leak test.
- Flow diagnosis (display group 020): During the flow test, the oxygen sensor control is switched off (engine runs rich during this time). At the same time, the secondary air injection pump is switched on. This supplies fresh air in the exhaust manifold, which increases the oxygen percentage in the exhaust. The heated oxygen sensor now measures a lean mixture. In order to pass the diagnosis, the heated oxygen sensor must measure a lean mixture over a defined period of time. This means that the secondary air injection system supplies a sufficient quantity of air-the secondary air injection system is OK.
- Leak diagnosis (display group 021): The requirement for the leak testing is first passing the flow testing. With the engine warm and idling, the secondary air injection pump is switched on. However, the combination valves are not triggered by the secondary air injection valve, i.e. they remain closed. When the secondary air injection pump is switched on, oxygen sensor control is observed by the ECM. If there are no leaks in the system, no fresh air can get into the exhaust manifold. Oxygen sensor control must practically not react (make richer or leaner). On the other hand, if the system has leaks, oxygen sensor control must react to the mixture that is now lean (by oxygen or secondary air injection) by making it clearly richer. This clearly richer state is recognized by the ECM.
Two methods exist for diagnosing the secondary air injection system (flow and leak diagnosis):
- Complete On Board Diagnostic (OBD) test of the system by the Engine Control Module (ECM) upon fulfillment of certain diagnosis conditions after each cold start; Display On Board Diagnostic results using the "Read Measuring Value Block" function 08, display groups 020 and 021 after the end of the diagnostic procedure; Recognized malfunctions are stored in DTC memory.
- Simplified shop diagnosis options using VAG 1551 with warm engine (shop diagnosis); Selective initiation of diagnostic sequence using "Basic Setting" function 04, display groups 020 and 021; Recognized malfunctions are stored in DTC memory.
Vehicle diagnosis ("Read Measuring Value Block" function 08)
Diagnostic conditions for flow diagnosis ("Read Measuring Value Block" function 08, display group 020)
- Coolant temperature from 8-55°C (46-131°F) at engine start
- No faults in DTC memory
- Engine running at specified engine speed/load conditions for longer than 12 sec. with active oxygen sensors
- Altitude display less than 48 Display group 001, display field 3
NOTE: The secondary air injection and thus the secondary air injection diagnosis will be interrupted as soon as:
- The engine speed is greater than 3700 RPM, or
- The engine load is greater than 70.4%, or
- The wide open throttle enrichment is active for longer than 5 sec.
After switching off the pump and before stopping the engine, the values must be displayed using the "Read Measuring Value Block" function 08, display field 4.
Diagnostic conditions for leak diagnosis ("Read Measuring Value Block" function 08, display group 021)
- No malfunctions stored in DTC memory
- Secondary air injection system testing ended
- Time after engine start: minimum 16 min.
- Engine coolant temperature greater than 70°C (158°F)
- Vehicle speed less than 6 km/h (4 mph)
- Closed Throttle Position (CTP) switch closed
- Altitude display less than 48 Display group 001, display field 3
NOTE: If these conditions are occur for longer than 2 sec., the AIR pump will be triggered for 10 sec. after a short delay period (the AIR control valve remains closed) and the leak testing will be carried out.
Shop diagnosis ("Basic Setting" function 04)
Diagnostic conditions for flow diagnosis ("Basic Setting" function 04, display group 020)
- Engine coolant temperature greater than 70°C (158°F)
- Closed Throttle Position (CTP) switch closed
- No malfunctions stored in DTC memory
NOTE:
- If these conditions are present, the secondary air injection pump and the secondary air injection control valve will be activated for 30 sec.
- After switching off the pump and before stopping the engine, the values are displayed using "Read Measuring Value Block" function 04, display field 4
- Testing is only possible one time per engine start. If the testing is supposed to be repeated, stop the engine and start again.
Diagnostic conditions for leak diagnosis ("Basic Setting" function 04, display group 021)
- No malfunctions stored in DTC memory
- Secondary air injection system flow diagnosis (Display group 020)
- Engine coolant temperature greater than 70°C (158°F)
- Closed Throttle Position (CTP) switch closed
NOTE:
- If these conditions are present longer than 2 sec., the secondary air injection pump will be triggered for 10 sec. after a short delay period (the secondary air injection control valve remains closed) and the leak testing will be carried out.
- Testing is only possible one time per engine start. If the testing is supposed to be repeated, stop the engine and start again.
Display groups 020 (Secondary air injection system flow diagnosis)
1) Diagnosis limit value in "Vehicle diagnosis" with "Read Measuring Value Block" function O8 in order to evaluate the diagnosis as OK, this value depends on the operating conditions during diagnosis.
2) Diagnosis limit value in "Shop diagnosis" with "Basic Setting" function O4 in order to evaluate the diagnosis as OK.
Note on display field 3: If the value drops below the required specified value during function testing while the customer is driving, a malfunction is stored in the DTC memory after 2 trips. Check DTC memory.
Note on display field 4:
- Value "0":
- No Value "1": Yes
The flow diagnosis is ended when the following status display appears:
- *1**1100: flow diagnosis OK
- *0**1100: flow diagnosis not OK
Values in places filled with * not important for flow diagnosis
Display group 021
1) Diagnosis limit value in "Vehicle diagnosis" with "Read Measuring Value Block" function O8
2) Diagnosis limit value in "Shop diagnosis" with "Basic Setting" function O4
Note on display field 3: If the value exceeds the permissible specified value during function testing, a malfunction is stored in the DTC memory. Check Diagnostic Trouble Code (DTC) memory.
Note on display field 4:
- Value "0":
- No Value "1": Yes
The flow diagnosis is ended when the following status display appears: "Vehicle diagnosis" with "Read Measuring Value Block" function 08
- 11111100: leak diagnosis OK
- 01111100: leak diagnosis not OK
"Shop diagnosis" with "Basic Setting" function 04
- 1*11**00: leak diagnosis OK
- 0*11**00: leak diagnosis not OK
Values in places filled with an asterisk (*) are not important for flow diagnosis