It had been sitting in my garage for 6 hours. I went out to throw some trash away and noticed a slight humming sound coming from the driver’s side rear. It sounded a little like a motor or a pump. After a couple of minutes it shut off.
What made the sound? why did it kick on even after the car had been shut off for 6 hours? Is it supposed to do that? How often would I expect this thing to happen?
(The only thing I can guess that’s back there is the fuel pump, but I don’t know why it would kick on spontaneously)
Is it possible that your keys are still in the ignition? Maybe the car isn’t as “off” as you think…
The other possibility is that there is a motion sensor on this car. Doubtful.
As a valet driver, I have noticed that certain upscale cars like Cadillac and Lincoln have pneumatic suspension components which maintain a level ride…often activating at apparently random intervals, after the car has been shut off.
I would check your owners manual first. Probably a waste of time though. I can’t think of any pump or motor that should come on while the vehicle is off. A call to one of the service advisors at your dealer might be a good idea. If it something normal they would most likely be aware of it and if they don’t have a clue I would take it to the dealer and let them figure it out.
Be cautioned it may take them a while to figure it out as they will have to duplicate the condition.
My first thought as my car has hydropneumatic suspension and on unlocking it whirrs and levels itself.
If left long enough unlocked it will `dance’ especially on uneven ground, until it goes into economy mode and shuts off everything electrical to prevent draining the battery.
The other thing is the lift pump in the tank, but that only ever activates when the ignition is on, before the engine starts, to prime the system.
There are posts here where people say new corollas have a sticker around the shifter that states the noise is from a routine check performed 5 hours after shut off. None of the people seem to remember exactly what is running, but I bet that’s the ballpark answer.
The wifey has a 2007 Corolla that does exactly the same thing. Scared the hell out of me when I was smoking a cigarette while leaning on the trunk at around 2 a.m.
control-z nailed it. Federal regulations require the engine management system to check the the fuel system for vapor leaks as small as 0.5mm.
Over the years there have been various strategies for doing this.
One very popular one is to use a pump after the engine has been off for a period of time. When the test starts, the pump fires up and pushes air though a 0.5mm calibrated hole. The ECU records the amount of current necessary to push air though this hole. This is called the reference phase. The the system switches and starts to pump air into the tank. As the tank pressurizes the current draw of the pump increases. When the pump current exceeds what the current draw was during the reference phase, the system knows that there is no hole exceeding 0.5mm in the system.
Pretty simple and very reliable.
Also some cars will turn on the heater fan on high for 5 minutes or so after the car has been parked for a while, to dry the evaporator out and prevent mold, mildew, and smells.