here is a service bulletin on this
Bulletin No.: 06-01-39-002C
Date: January 18, 2008
Blower Motor Inoperative or May Not Shut Off in Extremely Low Ambient Temperature Conditions (Replace Blower Motor Control Module)
2004-2007 Buick Rainier
2003-2006 Cadillac Escalade Models
2003-2006 Chevrolet Avalanche, Silverado, Suburban, Tahoe
2003-2007 Chevrolet TrailBlazer Models
2007 Chevrolet Silverado (Classic)
2003-2006 GMC Sierra Models Yukon Models
2003-2007 GMC Envoy Models
2007 GMC Sierra (Classic)
2003-2004 Oldsmobile Bravada
2003-2006 HUMMER H2 Models
with Automatic Temperature Control HVAC System (RPO CJ2)
This bulletin is being revised to update the model years that are affected and add the Oldsmobile Bravada. Please discard Corporate Bulletin Number 06-01-39-002B (Section 01 - HVAC).
Some customers may comment that the blower motor is inoperative or continues to run after the vehicle has been shut off.
These conditions may be caused by a blower motor control module failure. This failure may occur when the vehicle is operated in ambient temperature conditions of-23°C (-10°F) or below.
Replace the blower motor control module if the vehicle experienced a blower motor control module failure in extremely cold ambient temperature conditions.
Technicians are to replace the blower motor control module also called the Linear Power Module (LPM) with the P/N listed below. Refer to either the Blower Motor Control Processor Replacement or Blower Motor Processor Replacement-Auxiliary procedures in SI. After replacement of the blower motor control module the customer may notice a slightly higher than expected blower motor speed at any of the blower speed settings.
For vehicles repaired under warranty, use the table.