First, it's electric and not belt driven. It only runs for about 2 minutes when the engine is cold and its purpose is to then help burn a rich mixture before the cat conv gets to its peak efficiency, by then the air pump is no longer needed.

When it's healthy, it'll sound like a mini-hand held vacuum cleaner (under the battery) but when its bearings are begining to go, it'll get very loud in comparison and that's when most customers hear it. It doesn't sound at all like an "engine noise" but then many customers also hear bad headlight wiper motors and say that sounds like an engine noise to them too.

When the shut off valve to it starts sticking (something you can't do anything about), excessive condensation forms ALOT of water that flows down the air hoses and into the air pump (where it can't escape from) and eventually the pump then siezes.

We replace many of these with weather changes when cold weather and/or alot of wet weather comes.