My GS 450h has always had a sound from under the hood when the engine isn’t running. It starts when you open the door. It sounds like a pump that cycles for a few seconds, then turns off. Repeat. Repeat. Etc.

I don’t notice it when the gas engine is running, but when stopped at a light with the engine off, you’ll hear it from inside the cabin. It’s occasionally accompanied by a louder clunking sound.

When you turn the car off to get out, it will continue to cycle, but eventually stops.

Does anyone know what this sound is, and is it expected behavior?

 

brake actuator I think. my gs460 does it too.

 

Thank you. My car is in the shop and they say I need to replace the brake actuator. Simultaneously, the battery died while in the shop. They say it's because the brake actuator runs when the car is off. It's an independent Lexus shop, but I'm really concerned they don't know what they're doing.

 

from your other post, it sure seems like they don't know what they are doing. I think you'll know when your brake actuator goes bad, because im pretty sure it will be making that buzzing sound constantly even when the car is running.

 

First step: check where the sound is coming from. If its coming from the top right side, what you’re hearing is probably the ABS Brake Actuator.
It’s a large aluminum block with several metal brake lines snaking out of it.

Is it normal to hear it for a 3-5 seconds when you open the driver's door. That’s just the electric pump "priming" the brake system because these cars don't use engine vacuum for the brakes.
On the other hand, it's not normal to hear it every few seconds. Most probably the system is losing pressure internally and the pump is working overtime to keep you from losing your brakes.


Next time you're in the car try this:

1. Park the car, stay in "Ready" mode, and keep your foot off the brake.
   
2. Time how long it stays quiet.
   
3. If it’s buzzing every 15–20 seconds without you even touching the pedal, your actuator is on its last legs.
   
   

The problem is that these units are expensive. Try to check for any codes using a decent scanner.
If the cycling gets faster, don't ignore it, if that pump burns out from running too much, you’ll have about 5% braking power left. which ...well..you figure it out.