| Subject: | Information on LMG, LC9, LY5, LH6, L76 Change in Exhaust Tone or Sound For Active Fuel Management (AFM) System Equipped Engines in Four Cylinder Mode |
| Models: | 2007 Buick Rainier |
| 2007-2008 Chevrolet Avalanche, Silverado, Suburban, Tahoe, TrailBlazer |
| 2007-2008 GMC Envoy Denali, Sierra, Yukon, Yukon XL |
| with Active Fuel Management System Vortec® GEN IV 5.3L or 6.0L V8 Engine (VINs 0, 3, J, M, Y -- RPOs LMG, LC9, LY5, LH6, L76) |
This bulletin is being updated to include 2008 models. Please discard Corporate Bulletin Number 06-06-05-001A (Section 06 -- Engine/Propulsion System).
Some customers may comment on a change in the exhaust note or tone when an Active Fuel Management System equipped engine is in 4 cylinder mode. Some drivers may also notice a very slight vibration in either the accelerator pedal, floor pan and/or the steering
wheel. This is a normal condition for Active Fuel Management System equipped vehicles and no repairs should be attempted.
Customer Information on Active Fuel Management
When the Active Fuel Management System is enabled, physical changes take place within the engine that allow it to run as a 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. You may give a copy of this bulletin to your customer.
