2008 GMC Yukon Owner's Manual - Page 407

Engine Fan Noise If your vehicle has a clutched engine cooling fan, when the clutch is engaged, the fan spins faster to provide more air to cool the engine. In most everyday driving conditions, the fan is spinning slower and the clutch is not fully engaged. This improves fuel economy and reduces fan noise. Under heavy vehicle loading, trailer towing, and/or high outside temperatures, the fan speed increases as the clutch more fully engages, so you may hear an increase in fan noise. This is normal and should not be mistaken as the transmission slipping or making extra shifts. It is merely the cooling system functioning properly. The fan will slow down when additional cooling is not required and the clutch disengages. You may also hear this fan noise when you start the engine. It will go away as the fan clutch partially disengages. If your vehicle has electric cooling fans, you may hear the fans spinning at low speed during most everyday driving. The fans may turn off if no cooling is required. Under heavy vehicle loading, trailer towing, and/or high outside temperatures, or if you are operating your air conditioning system, the fans may change to high speed and you may hear an increase in fan noise. This is normal and indicates that the cooling system is functioning properly. The fans will change to low speed when additional cooling is no longer required. Power Steering Fluid See Engine Compartment Overview on page 5-14 for reservoir location. If your vehicle is a Two-mode Hybrid, see the Two-mode Hybrid manual for more information. When to Check Power Steering Fluid It is not necessary to regularly check power steering fluid unless you suspect there is a leak in the system or you hear an unusual noise. A fluid loss in this system could indicate a problem. Have the system inspected and repaired. 5-39