2008 Gmc Sierra Making Noise From 2nd To 3rd Gear

norcalZ71 · July 5, 2008

Basically when i'm driving and the truck is going from 2nd to 3rd, you'll hear a slight drone sound...nothing crazy but you can hear it and sometimes you can feel it slightly in the gas pedal and floor board.

Took it to the dealer a couple weeks ago, a Tech rode with me and I pointed it out to him and he could also hear/feel it. They kept it overnight and said the TSB #06-06-05-001B (service bulletin) says its due to the AFM (active fuel managment) and no repair is needed. (I have a copy of the TSB)

But my concern is that it's something else...the TSB they gave me is not real clear and to me states that this problem is when the truck is in V4 mode, which wouldn't apply to going from 2nd to 3rd as it would be in V8 mode then correct?

It has just over 3,000 miles on it, has only been making the sound for a couple weeks...could it be that I need to change the oil? Haven't done so yet.....

Anybody have any advice???

Thanks!

jrrod2004 · July 6, 2008

For everybody else that does not know what that TSB says:

(06-06-05-001B)

Service Information

Document ID: 2072530 #06-06-05-001B: 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 - (Feb 26, 2008)

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

2007-2008 Saab 9-7X

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.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

jrrod2004 · July 6, 2008

The sound should only manifest itself when the truck switches over to the V4 mode, it should not be apparent when the truck is in full (V8) mode.....the way you describe it matches this TSB

norcalZ71 · July 6, 2008

The sound should only manifest itself when the truck switches over to the V4 mode, it should not be apparent when the truck is in full (V8) mode.....the way you describe it matches this TSB

hmmm...the only time I hear the sound is from 2nd to 3rd gear. Correct me if i'm wrong but in those lower gears (when taking off from a stop for instance) the truck would be in V8 mode.

V4 mode is only when coasting or driving at a steady speed...not when the rpm's are up and you are changing gears correct?

I agree though, the discription on the TSB regarding the noise and feel through the floorboard etc.does match my problem, but I'm still not sold that is the problem.

this is a Z71 SLT that is loaded to the gills, it shouldn't be making odd sounds like this at 3,000 miles!

jrrod2004 · July 6, 2008

Let me keep looking, you are correct, the truck should only enter V4 mode when cruising with a light to no load. This usually appears with flat or downhill roads but some trucks have been reported to stay in V4 mode when going up a slight hill.