The secondary air pipe is part of the emissions system and channels fresh air into the circuit during cold starts, helping the engine reach clean-running conditions quickly. It works with other core system parts like the secondary air system pump (247795) and secondary air valve (284235) to keep airflow consistent through the secondary-air passages.
If the pipe splits, softens from heat or works loose at a joint, the car can log secondary-air faults and trigger annoying warning lights.