The air pump only does it's job for the first couple of minutes when the engine is first started. This is to enhance the rich cold start mixture with O2 to keep the smog level down until the cat can warm up to effective temps.

In Europe (Germany, especially), smog tests are performed about 60 seconds after the engine is started...so the smog levels have to be on target soon, hence the accessory air pump.

In the US, this component is unneccesary, but I don't know CAL laws. The absence of the pump might not pass inspection.

When the pump bearing fails, it will start to seize up and trash the belt. Not sure what it sounds like, but it's ugly. You can't just crack the case and rebuild it, since the bearing is not a readily available unit (probably deliberate since it is a smog-certified unit).

It can be disconnected (there are threads on this) so the clutch does not engage the pump...no need to swap out a belt to bypass the air pump pulley.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car