When checking automatic transmission fluid, what is the proper engine condition?

When checking automatic transmission fluid, it is important to have the engine running and the transmission in Park to ensure an accurate reading. When the engine is on, the transmission pump circulates the fluid, allowing it to reach operating temperature. This is crucial because the fluid expands when it's warm, and checking it cold may lead to an inaccurate level reading.

With the transmission in Park, the fluid is contained, providing a stable condition for measuring the level. This ensures that the fluid level is where it needs to be for proper lubrication and operation of the transmission components. Proper fluid levels are essential for the smooth operation of an automatic transmission, and following the correct procedure helps prevent issues related to fluid starvation or overheating.