Low Speed Operation
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 ECM applies ground to the coil side of the cooling fan low speed relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the low speed relay. The left cooling fan is connected in series to the right cooling fan through the de-energized series/parallel (S/P) cooling fan speed control relay. The result is a series circuit that operates both fans at low speed.