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 control circuits, 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 cooling requirements. The ECM controls the five relays by grounding the relay control circuits.

To operate the fans, the ECM activates the applicable relay by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage. When the ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage of the control circuit should be high, near battery voltage.