I just noticed a rattle/humming sound when starting my 2015 Toyota Highlander. It happened 3 times, all in the last week or so. It could be cold-related (around freezing temps). It sounds like some electric motor, similar to what a large computer fan would do. From the cabin, it was clearly louder than the rest of the car engine. Car heating and fan was off.

I immediately parked, and it continued for about 5 seconds, when I stopped the car, after cutting the engine. So, I ruled out:

  • rattling object in the car
  • heating/fan

I assume there is some pump or other component that could produce this sound. Pump that maintain oil pressure, maybe ?

I'm wondering what those components could be ? How critical could such a sound be, e.g. how urgently should I go back to the mechanic/dealership ? There are no check-engine lights or anything else indicating a problem.

Edit: regular V6 engine, not hybrid or anything.

  • Does your car have self levelling suspension?
    – HandyHowie
    Dec 22 '15 at 17:00
  • Did the sound resume when you restarted the car? Dec 22 '15 at 17:55
  • The sound did not return after restarting the engine.
    – Jeffrey
    Dec 22 '15 at 18:52
  • @HandyHowie: No idea :-). Didn't know such a thing existed. Unless it is standard issue for Toyota Highlander.
    – Jeffrey
    Dec 22 '15 at 21:00
  • So, did you found the problem? I have a similar sound on my 2014 Highlander when it is cold. Sound starts when temperature is lower than -5 Celsius and about 4 minutes after the engine is started.
    – Balinus
    Nov 20 '18 at 1:48

This is apparently a normal sound. The vacuum pump, according to Toyota, can run at any time. It is required for emission control. And, depending on various conditions, can be much louder or quieter.

My understanding is that this pump is a part of secondary air injection. The injected air location varies with the engine temperature, according to the link above. So, outside temperature could affect operation (and noise).


Take it to the dealership ASAP. Not the kind of noise you want to ignore or even try to diagnose on here. Leave it overnight for them to check on cold-start and cold temperature.

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