Anyone know what sensor is monitored to activate the air pump and what the temp values are for cut in and cut out? It seems the pump only comnes on in the really cold weather, thus accounting for the marked increase of posts on the Brickboard relating to pump failures and noises.

Doug I just had this done under warranty.The pump should only come on when the engine is cold.It aids in reducing cold start emissions.If it is noisy,then it is beggining to fail.The pump and valve were replaced under my extended warranty.The valve is located on top of the turbo with the rigid line that connects to your downpipe.For some reason Volvo says these pumps fill with condensation and rust out.My check engine light came on when the pump totally failed.

I am aware of all those points you make. My question is however, at what temp does the pump come on? Below 32? 25? who knows? where is the sensor for this?? I fixed my own pump and beat Volvo out of a non-warranty repair and part sale. These pumps are still failing years after having the check valve and original pumps replaced.

What kind of warranty covered the pump's replacement? Mine is noisy this year, and the Certified warranty doesn't cover it. Personally, I'm inclined to let it fail as (according to the dealer) it's not going to take anything else with it except my emissions.