| Because of the over-enrichment of the mixture in the cold start phase, the proportion of unburned hydrocarbons in the exhaust gas is higher. The secondary air system improves the afterburning (oxidation) process in the catalytic converter, and thus reduces toxic emissions. The heat generated by oxidisation accelerates the light off of the catalytic converter and significantly improves exhaust gas quality during warm-up. |
| In the warm-up phase, the engine control unit activates the secondary air pump via the secondary air pump relay. The stream of air from the secondary air pump opens the combination valves for secondary air and lets air flow into the exhaust system upstream of the catalytic converter. |
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