Which fluid level should be checked while the engine is running?

Checking the transmission fluid level while the engine is running is crucial because the transmission requires the circulation of fluid to provide an accurate reading. When the engine is on and the vehicle is in park or neutral, the transmission pump circulates the fluid throughout the system, allowing it to reach the correct operating temperature and pressure. This ensures that the dipstick provides an accurate measurement of fluid levels.

In contrast, fluids such as oil, coolant, and brake fluid should be checked when the engine is off to avoid injury from hot components or moving parts. Checking these fluids while the engine is running could lead to inaccurate readings and safety hazards, as the fluctuating levels due to engine operation might mislead a technician regarding the actual fluid status. Therefore, it is essential to follow the proper protocols to maintain accurate assessments of fluid conditions for safe operation.