Clicking noise during Pilot assist use

[akshaykakkar]

Hello everyone,

I have a pretty recent Volvo S90 which has done 15K miles.

During few of my drives recently, I have started noticing a sound when I use Pilot Assist or ACC.

The clicking noise is produced (like a relay click) when either Adaptive cruise control or Pilot Assist are in operation and the car in front of you is slowing down. So the car automatically applies brakes to slow down & this is when the sound comes up.
Similarly when you accelerate from standstill after a few seconds, it comes up again and vanishes as the car speeds up.
The sound lasts no more than 4-5 seconds (while slowing down to a stop & while accelerating from 0)

This does not happen when driving control is with me, so no clicking sound when I am pressing the brake pedal or accelerating by myself.
This makes me believe that there is nothing wrong with brakes because it would create the same noise when I manually use them.

Do you know if this is normal behaviour? Or is this something that could be a problem with brakes or something I should be concerned about?

Regards,
Akshay

[nu11eaf]

Its not normal, I have never heard any noises when using ACC or PA.

[scw]

My XC60 has always made the same slight clicking noises from the driver's footwell while using ACC in traffic.

I recall a thread a year or two back where others reported the same thing, so I don't think it's anything out of the ordinary or worth worrying about.

Steve

[istanbul]

Originally Posted by akshaykakkar

Hello everyone,

I have a pretty recent Volvo S90 which has done 15K miles.

During few of my drives recently, I have started noticing a sound when I use Pilot Assist or ACC.

The clicking noise is produced (like a relay click) when either Adaptive cruise control or Pilot Assist are in operation and the car in front of you is slowing down. So the car automatically applies brakes to slow down & this is when the sound comes up.
Similarly when you accelerate from standstill after a few seconds, it comes up again and vanishes as the car speeds up.
The sound lasts no more than 4-5 seconds (while slowing down to a stop & while accelerating from 0)

This does not happen when driving control is with me, so no clicking sound when I am pressing the brake pedal or accelerating by myself.
This makes me believe that there is nothing wrong with brakes because it would create the same noise when I manually use them.

Do you know if this is normal behaviour? Or is this something that could be a problem with brakes or something I should be concerned about?

Regards,
Akshay

This is totally normal, what you hear is the noise of relay working. When the sensor triggers, system activates acceleration, breaks, steering motor etc. based on the input. Computer gives signals with a very low voltage to the relay and relay turns the actual switch of respected mechanism on an off.

At the beginning, it was also weird to me but later I recognized, it is the working sound. I would also prefer not to hear this operation but, nothing to worry.

PS: You will hear similar in the case where driver is on control but you approach a bit too close to the car in front of you, then the automatic break system gets prepared.

[Boatie]

Not a sound I've heard in either of my V90s (both with PA and ACC). Going back to a previous era of basic electrics it sounds like a relay is not 'latching' when energised. I'm sure that some oldies will remember a chattering starter solenoid. Normally a poor connection.

[Carabind]

I have similar on my s90. It come on as the car is braking . I assume its some sort of power source (electrical or hydraulic) taking over brake operation . Audible but I filter it out as a known characteristic. I also get a gurgling from behind the centre console, but believe that’s the air conditioning fluid “boiling off” or similar

[Fursty Ferret]

Pilot Assist / Adaptive Cruise doesn't work with relays. They're binary / on-off actuators. The click might be a relay (although I doubt it since solid-state stuff is more reliable) but is more likely to be one of the switches behind the brake pedal engaging, as the pedal moves slightly when the system brakes.

[akshaykakkar]

So I tried recording it through a passenger & here's what i could manage.

https://www.youtube.com/watch?v=D9aX4UsXZL0

There is ambient car sound so you'll need to turn up the volume, but you could hear this sound at the following intervals in this 8 second video:
1. Starts at 2 seconds
2. Between 5 and 7 sections

It sounds more like bird chirping and this happens when ACC or Pilot assist is slowing the car down. When I use brakes manually (press the pedal by myself) this doesn't happen.

Anyone heard of something similar?

[nu11eaf]

I never hear that or any other sound like that on my car.

[Kingston1]

Yep, I also have the same noise in my V90. Initially I didn't hear it as I usually have music playing but a few weeks ago the music was off and I could clearly hear the clicks as the brakes applied and released.
I suspect it's normal.