I have a 2004 Trailblazer. When you kill the engine you can hear something still running (sounds like a humming noise or perhaps a fan blowing) This occurred the other night and the next morning I tried to start the truck and the battery was dead. My husband found the relay switch/fuse that according to the manual is the relay for the A.I.R. pump and disconnected it so as to not drain the battery once again. Just wondering what this A.I.R. pump is responsible for and if it is hurting us to run the truck without it until we get it replaced??? Thanks!

 

The secondary air injection system is designed to add filtered air into the exhaust manifold to help complete combustion of products in the exhaust gases and minimize pollutants. An air line comes from near the air filter and leads through the pump and then to a check valve on the manifold.

During normal operation the system runs for about 30 seconds when the engine is started cold. As soon as the exhaust gas temp rises the pump turns off. The check valve opens when the pump is running and closes when the pump stops.

A fairly common problem is for either the check valve or the pump to fail.

If it is indeed the Secondary Air Injection pump that is running after the engine turning off a warm engine then you definitely have a problem. If the pump is running normally but just fails to turn off the relay might be frozen. The relay can be purchased as a separate part without having to buy the pump as well.

To answer your question, you can run the vehicle without the pump operating but I would repair the problem as soon as possible.