The main reason you should check under the hood is:

The primary reason for checking under the hood is to verify fluid levels. Regularly inspecting fluid levels, including oil, coolant, brake fluid, and windshield washer fluid, is essential for maintaining the health and performance of your vehicle. Adequate fluid levels prevent overheating, ensure proper lubrication, and support overall engine function. This practice is a critical part of a vehicle's preventative maintenance routine, helping to identify potential issues before they lead to significant problems. While checking spark plugs, the lighting system, and the engine compartment might be important for specific maintenance tasks, monitoring fluid levels is fundamental for engine operation and safety.