Secondary Air System, Principle and Function

Secondary Air System, Principle And Function

Principle
Because of the over-enrichment of the mixture in the cold start phase, the percentage of unburned hydrocarbons in the exhaust gas is higher at that time. The injection of secondary air improves the post-oxidation in the catalytic converter and thus reduces pollutant emissions. The heat produced by the post-oxidation considerably shortens the start-up time of the catalytic converter and significantly enhances the emission quality in the cold-running phase.

Function
- During the cold start phase (coolant temperature at +15... +35 degrees C) the secondary air system blows air behind the exhaust valves for approx. 65 seconds. This produces an oxygen-rich exhaust gas, causes after burning and reduces the heating-up phase of the catalytic converter.
- In addition, 20 seconds after each following engine start (until coolant temperature reaches 85 degrees C), the secondary air system switches on for 5 seconds when at idling speed and is checked by the self-diagnosis.
- The Secondary Air Injection (AIR) pump motor -V101- is actuated via the Motronic Engine Control Module (ECM) -J220-, the Secondary Air Injection (AIR) pump relay -J299-, the Secondary Air Injection (AIR) solenoid valve -N112-, the change-over valve and the combination valve.