Heater with in-line pump

[Brianrzr]

I have the heater option, in between the engine and the heater core is a in-line pump. What is it’s purpose, and when does it turn on? I assumed it is powered when the heater is turned on, but it appears that it is not. My heater blows very hot air so I know it is getting water flow. I’m just curios how it functions. Thanks.

[UNSTUCK]

Some engine water pumps can't push the hot coolant all the way up to where the heater core is...usually around the helm. In these cases they install a transfer pump to help push the coolant the rest of the way. If your transfer pump is not running and you're still getting hot air, you probably didn't need it in the first place.

[freeheel4life]

Brian,
I believe your year the pump is tied to ignition circuit (purple wire). I believe if you key to IGN it will come on. Always takes some fiddling to figure out though as it seems like these things literally change year to year. I believe 14s and up the pump became standard if you ordered a heater

[KoolAid]

They are tied into the fuel pump wiring on the engine with a relay set. The pump operates when the engine is running. I know for sure the 2015's and up have it. Not too sure about the 14's since they were the GM blocks.