humming with truck off..

The other day I was messing around in the garage and heard a faint buzzing sound. Started looking around and couldnt find it.
This afternoon I was in the garage again and I heard the buzzing sound again. Sounds like a small electric motor running. I opened the garage door to see if the neighbors were doing something that was maybe vibrating somethin in my garage. After walking around the garage and not being able to pin point anything. I look at my truck and think to my self.. "I guess ill check" so as I get underneith it its clearly the truck. Above the rear of the gas tank close to the frame crossmember there is a big black box that vibrates (haha no pun intended) now im not real firmiliar with these trucks. the lines and hoses coming off it seem to go to the fuel tank. Is the fuel pump on the outside of the tank on these?? And why is it running? It runs for about 5 minutes and quits and has not done it since. the truck was cold and hadnt been driven or even had a key put in the ignition for about 4 hours. So im going to keep an eye on this as ill be spending some time working on a wood project in the garage for a few days. Anyone else come across something like this. It runs and shuts off on its own so I dont assume theres a short or anything.. Taco is brand new maybe something crazy that ive never heard of??

 

It's something to do with the gas evap system I believe

 

Evap emissions purge pump. It pulls the vapors collected by the charcoal canister and pumps it back to the fuel tank. It also runs an evaporative emissions test at the same time.

 

wild. How often does it do this?

 

Okay, I double checked my facts. The noise you are hearing is actually only an air pump to pressurize the fuel tank to perform the leak-down test that I mentioned earlier (it will throw a CEL code if the pressure is lost too quickly). Purging of the canister will occur while the vehicle is running.

So anyway, it should perform the test after every few hours of engine run time. But as you noticed it needs to have cooled off before the test will be accurate.

 

Interesting. Well its news to me, at least its normal ha. Thanks for the info.

 

Both my '13 Taco and the wife's '12 RAV4 do it. Sometimes I'll go out to the garage to do something and both of them will be humming along. The manual says it's normal.

 

Same noise on 2016 Toyota Tacoma. Thank you very much from San Diego, CA.

 

Found this thread after hearing the same exact noise from my '16 just now. Truck has been off and in the garage for about 6 hours. Didn't do anything when this sound randomly came on. Definitely coming from the same area that has been described in OP - black box above the gas tank.

Thanks for the info.

 

When did they start using this system, never heard that noise before?

 

Mine too and great more electrical nonsense to fail.