I have a 2011 Silverado CC SB with the 5.3 and 6 speed auto. when the Active Fuel Management thing cuts down to V4 mode, the whole truck just has a violent vibration like when your driveshaft isn't balanced but worse. vibration is much worse at around 50-60 mph. Is this normal or is it something i should get checked out?

 

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A slight vibration is normal.

When the Active Fuel Management System is enabled, physical changes take place within the engine that allow it to run as a 3 or 4 cylinder motor with accompanying additional fuel savings. The change in exhaust tone is expected as all sound from the exhaust is the result of combustion in the engine. The ability to perceive these changes in sound are kept to very minimal levels as the Active Fuel Management System is only activated during steady state/near steady state driving or during coast down. In both of these situations, the load on the engine is minimal and general exhaust volume (sound) is low.

If you are experiencing more than a slight vibration, I recommend having the vehicle inspected by a certified technician.

Please keep us posted. If you have additional questions, please feel free to contact me privately.

Louis
GM Customer Service