You need to first retrieve codes stored and see where the problem is likely to be after investigating the codes stored (I am presuming there is a check engine /service engine soon light on). It's an electrically operated valve secured to the engine by two bolts, it has a 5 wire connector on top of it on the fan belt side of engine on top. Call the dealer with your VIN# there was a GMC recall on some of those.
Had a problem with this. Turned out the fuel injectors were leaking gas and it was laying around on top of the engine. Glad it did not ignite! After you shut motor off, immediately pull engine cover in cab and check top of motor for gas.