For the 2nd time in a month, I walked in the garage after the car sat for a solid 12+ hours and could hear some kind of pump running. It wasn't the sound of a fuel pump but, sounded more like some kind of emissions air injection pump coming from the rear of the car. After about 10 minutes, I heard it turn off but, no clue how long it was running or why. Anyone ever heard of this or have a clue what could be cutting on with the car off and sitting idle in the garage?

FYI - This is on a '13 GS.

Thanks - Todd

 

I think it has something to do with the brake lines.

 

I just did a google search(should have done it first) and tons of posts about this happening 5+ hours after a Lexus is parked and dependent on how much gas you have and the temperature. All indications are that it is an emissions/gas vapor pump check.

 

It's the fuel evaporation leak check. It's normal. Many posts on the subject, just search.

Edit: I see you found this as I was posting.

 

The humming noise you hear coming from under the vehicle hours after turning Off the engine is the fuel evaporation leak check. Any time up to approximately 5 hours after the engine is turned Off, you may hear a humming sound coming from under the vehicle that could last up to several minutes. This is the sound of a fuel evaporation leakage check and, it does not indicate a malfunction. It is a normal occurrence and an expected event.

 

Page 8 of the owner's manual.

 

Well how abut that: 'rtfm' is still a valid response to so many questions.