Secondary Air Injection (Air) System

On Board Diagnostic Functions
- Diagnostic Trouble Code (DTC) Memory.
- Output Diagnostic Test Mode (DTM)
- Basic Setting.

NOTES:
- The secondary air injection system injects air behind the exhaust valves during a cold start. Cold start means engine coolant temperature between 8 - 65 °C (46 - 149 °F). The amount of air injected is temperature dependent.
- The need for secondary air is triggered by the Motronic Engine Control Module (ECM) -J220- via the Secondary Air Injection (AIR) Injection pump relay -J299- to the Secondary Air Injection (AIR) solenoid valve -N112- and the two combination valves.
- When "Basic Setting" (scan tool function 04) is initiated, a diagnosis for the secondary air injection system can be carried out. The diagnostics consists of a flow test and a leak test.

Flow test
During the flow test, the oxygen sensor control is switched off (engine runs rich at that time). At the same time the secondary air injection pump is switched on, injecting fresh air into the exhaust manifold which increases the oxygen content in the exhaust gas. The oxygen sensor now measures a lean mixture. To pass the diagnostic test, the oxygen sensor must measure a lean mixture for a certain time. Passing the test means that the secondary air injection system delivers enough air and the secondary air injection system is OK.

Leak test
- Flow test must check out OK
- Engine at operating temperature

The secondary air injection pump is switched on during idle. Since the combination valves are not triggered by the secondary air injection solenoid valve, they remain closed. When the secondary air injection pump is switched on, the oxygen sensor system is monitored by the ECM. If the system does not leak, fresh air cannot enter the exhaust manifold. If the system is leaking, the oxygen sensor signal will respond to the leaner mixture (caused by the secondary air getting into the exhaust manifold) and cause a noticeable enrichment. This enrichment is recognized by the ECM.