If you hear this weird noise coming from the back of your Toyota, even though it’s been parked for hours, there’s nothing wrong and here’s why.

Here’s the scenario, you’ve come home from work at around 6 P.M. parked your Toyota in the driveway, had dinner, relaxed, but forgot something in your car. It’s close to 11 P.M. now, and after you grab your stuff from the trunk of your car, you hear this whirring sound coming from the rear, like there’s a tiny motor running inside your gas tank or something. The keys are nowhere near the ignition, the engine stone cold after sitting for hours.

If you hear a sound coming from the back of your Toyota after about five hours, it’s not only perfectly normal, it’s something most cars, not just Toyotas, do. It’s called an EVAP test, and it’s even spelled out in your owners manual.

Here’s an example of the noise and a screenshot of the owner’s manual from a 2020 Toyota CH-R.

What’s an EVAP test?

Your car’s Evaporative Emission Control System (EVAP) is a closed circuit system that ensures vapors coming from your car’s fuel system do not vent outside. Even at temps as low as -40F, gasoline emits vapors that, if improperly vented, can combine with air to form smog. The EVAP system ensures vapors are stored and properly burned after being re-introduced through the intake manifold.

An Evaporation (leakage) test uses your car’s fuel pump to pressurize your car’s system to test for tiny leaks. Your Toyota is programmed to run this test after five hours because by that time, everything metallic has contracted, making leaks easier to find if present.

If a leak is found, your car will throw a Check Engine Light. The problem might be as simple as a loose gas cap or there’s an actual leak, it’s size, as small as a pin head.

Almost all cars with OBD-II systems carry out this test but it seems Toyotas make the most noise. I found this out, probably like you, when our family’s 2006 Toyota Corolla was making strange noises in the garage hours after we shut it off.

So, if you hear a whirring noise from your Toyota near the gas cap, it’s normal and no cause for alarm.


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