Low volume tone heard from engine after stopping.

Faults and Technical chat for the Skoda Karoq
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karoqkar
Posts: 19
Joined: Mon Jun 28, 2021 7:57 pm

Post by karoqkar » Tue Jul 26, 2022 8:18 pm

I have 1 year old Karoq petrol and this may have always been happening ?? Doesn't show alarm etc..??
When I switch the engine off after doing a run and get out of car, lock the car etc, as i walk away I can hear a Low volume tone of pitch about 1 kHz approx coming from engine under the bonnet. Sounds a bit like a switched mode power supply or something electronic or a small dc motor whining...??? It stops after about a minute or so.
There are times the radiator fan would be running after stopping engine.... but this tone is not that.
I have lifted the bonnet and listened around, I think it comes from something mounted on the engine rather that a device mounted on the chassis under bonnet.
I dont think it is a fault but curious to find out...??

Routemaster1
Posts: 49
Joined: Mon Jun 07, 2021 8:16 am
Location: Dorset

Post by Routemaster1 » Wed Jul 27, 2022 7:24 am

All modern cars do that. Don't know what it is, but certain functions seem to remain running for a minute or so. Quite normal so nothing to worry about.

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kodiaq
Posts: 738
Joined: Fri Aug 31, 2018 6:33 pm
Location: Poole, Dorset.

Post by kodiaq » Wed Jul 27, 2022 9:42 am

It is the electronic circuitry shutting down. All the chips and ECUs spooling down.
Nothing to worry about.
Colin Lambert.
Poole, Dorset.
Diploma Auto Eng.
Moderator Karoq & HR-V Fora.
(Kodiaq Forum Moderator, resigned!)

karoqkar
Posts: 19
Joined: Mon Jun 28, 2021 7:57 pm

Post by karoqkar » Wed Jul 27, 2022 2:12 pm

Thanks for replies, thought there might be some info more specific to the Karoq..??
I assume the Karoq has an electric LP fuel pump in the tank and a camshaft driven HP pump on the engine, maybe the HP one is electronically controlled as well..?
Maybe electronic pressure control to control the common rail pressure..?? and then electronic control for the injectors etc. And then the ignition system maybe a HT switched mode PSU for its supply all controlled by the ECU...??? So which is causing the tone..??.... So just guessing the tone could be from the ignition supply oscillator OR the PCM/PWM control for the injectors..??.
Maybe its a bit like the old flourescent lamps if they were going to be switched on and off within a 15 minute period it was more economic to let them stay on..??
So maybe to allow for possible engine restart within a minute or so it is better to keep the PSU and oscillators running for a short period...??

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