Owner Letter

Customer Copy

December, 2006

Dear Valued General Motors Customer:

Subject:
Added after market transmission sump heaters used in:

2006 Chevrolet Silverado 2500 (3/4 Ton) and 3500 (1 Ton)
2006 GMC Sierra 2500 (3/4 Ton) and 3500 (1 Ton)
2007 Chevrolet Silverado Classic 2500 (3/4 Ton) and 3500 (1 Ton)
2007 GMC Sierra Classic 2500 (3/4 Ton) and 3500 (1 Ton)

Equipped with 6.6L Duramax(TM) Diesel Engine (VINs D, 2 - RPO's LBZ, LLY)

and Allison(R) LCT 1000 (RPO MW7) Six Speed Automatic Transmission

General Motors is committed to customer satisfaction and we want you to have absolute confidence in our products. Our records indicate you may currently own one of the vehicles listed above. This letter is to advise you of a potential product concern, which could occur if an aftermarket transmission sump heater has been added to your vehicle.

If an aftermarket transmission sump heater has been added to your vehicle, it may be susceptible to transmission failure when all of the following conditions exist:

The vehicle is exposed to -40°C (-40°F) for more than 8 continuous hours (cold soak)

An aftermarket transmission sump heater has been added to the vehicle

The aftermarket transmission sump heater is active

The vehicle's Elevated Idle Mode is engaged (refer to Owner's Manual for details to determine if your vehicle has this feature engaged)

When a vehicle has been exposed to this extreme cold temperature for an extended period of time, the fluids become very thick. An aftermarket transmission sump heater warms the transmission fluid in the transmission, allowing it to operate. However, since the aftermarket heater does not warm all the transmission fluid, such as that fluid located in the cooler lines and transmission oil cooler located in the radiator, that fluid remains very thick and cannot flow. When the Elevated Idle Mode is engaged the transmission temperature could increase to a level that may cause damage to the transmission.

If you own one or more of the vehicles described above with an aftermarket transmission sump heater, we recommend you have the Transmission Control Module (TCM) recalibrated to accommodate the effect of the aftermarket sump heater and eliminate this potential over temperature concern. This recalibration is beneficial only on vehicles located in extreme cold climates with all the conditions listed above. Disabling the Elevated Idle Mode is an interim action that will protect the transmission prior to the TCM recalibration being performed. Elevated Idle can be engaged or disengaged using the driver information center controls or by the following method.

Turn the ignition to RUN, with the engine off.

Press the accelerator pedal to the floor and hold while quickly pressing the brake pedal three times in less than eight seconds.

Release the accelerator pedal and start the engine.

Please contact your local GM Dealership at your earliest convenience and reference this letter when scheduling an appointment. Since this recalibration is only necessary to accommodate the effect of an added aftermarket transmission sump heater, you would be responsible for the cost to recalibrate the TCM. Your dealer can advise you of the cost to perform this service.

Damages resulting from aftermarket modifications are not covered by your vehicle's GM Warranty.

We regret any inconvenience this may cause; however, we are making this correction available in the interest of your continued satisfaction with General Motors products.