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Home >> GMC >> 2006 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1539 (Engine Cooling System - Non-Hybrid) >> Diagnostic Information and Procedures >> Cooling Fan Always On (with HP2) >> Circuit/System Description

Circuit/System Description

WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The hybrid engine cooling fan system consists of two electrical cooling fans, two resistors, three engine control module (ECM) fan output control drivers, and five fan relays. The relays are arranged in a series/parallel configuration that allows the ECM to operate the fans at low, medium, or high speed depending on engine cooling requirements. The ECM controls the five relays by grounding the relay control circuits.