I hear a humming sound under my 2015 Highlander when its not running
Because it is, it's the cooling fan, when it reaches a certain temperature it shuts off on it's own, this is normal.
When the car cools down from running or just from sitting in the garage when it is warm outside?
Mine does this as well. It is hours after the vehicle has been in use and the sound comes from under the passenger rear. I will forget about it, then walk out in the garage and hear it again. I really don't think it's the cooling fan when it hadn't been driven for 5 hours and it is 63 in my garage.
Had a similar problem. My service advisor was able to find the issue. Something to the effect of "Servo motor Making noise per TSB-0048-16". "Replaced servo motor per TSP and installed insulation sheet per TSB. Renationalized servo motor." It is covered by warranty. It seems the dealership may push back because they want to charge you labor but they shouldn't because it is under warranty.
Happened to my 2016 Highlander too after resting 9 hrs, in my garage,
I just bought a 2017 Highlander and it did the same thing after sitting in my garage for about 8 hours. The deal said they didn't know what I heard even though I had a video of it, not very helpful. Did anyone get this fixed and if so what was the problem
Our 2013 Highlander was making a similar noise from under the rear passenger side and I found this on page 25 of the owner's manual: "Approximately five hours after the engine is turned off, you may hear sound coming from under the vehicle for several minutes. This is the sound of a fuel evaporation leakage check and, it does not indicate a malfunction."
Similar to Alfie's answer above, Our 2016 Highlander was making a similar noise from under the rear passenger side and I found this on page 8 of the owner's manual: "Noise from under vehicle after turning off the engine" "Approximately five hours after the engine is turned off, you may hear sound coming from under the vehicle for several minutes. This is the sound of a fuel evaporation leakage check and, it does not indicate a malfunction."
This also happened to me with my new 2017 Highlander. I had to go into the garage around midnight. The car had not been driven for hours. I was investigating and the noise stopped as soon as I got in the car with the key in my hand. I have a call into my salesman to see if he's heard about this and if I should take it in to the dealer. I've only had the vehicle a couple of weeks.
See Owners Manual 2017 HIghlander - page 8 - "Noise from under vehicle after turning off engine".. explained well.
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