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I've just changed the battery on my wife's car, a 2010 Renault Grand Scenic 1.5 diesel, and when I started it up with the new battery and the switched it off I noticed an electrical buzzing noise coming from the engine.
Lasted for about 3 minutes then stopped. Tried it a few times and same thing every time..
Ideas?
Dozer valve in the air intake?
It's a six year old Renault..... Soon the lights will all go off when driving, the windows will open and close on their own and the wipers will switch on and off for no reason ... 😀
Left your pills under the passenger seat?
It's a six year old Renault..... Soon the lights will all go off when driving, the windows will open and close on their own and the wipers will switch on and off for no reason ...
Ahhh, the magnificent masterstroke of design that is the Renault UCH
Bee stuck in the engine bay?
12" purple headed womb ferret under the passenger seat?
Is it the fan?
I have no idea if cars even have fans these days?
Definitely the fan.
I was going to guess fan overrun...but it wouldn't kick in unless the engine was up to temperature.
Even vague modern cars do a bit of housekeeping under the bonnet when you turn them off. The buzzing could come from a number of sources, but the usual ones are:
1) EGR valve doing a pot shut down cleaning cycle
2) Coolant run on pump, er running on
3) Throttle body or idle air valve carrying out position adaption
All emit a faint hum which you can generally hear with the bonnet up, but generally not with it down.
Car should be fully asleep and quiet except for anti-theft/passive entry systems (ie alarm etc) after a max of about 10min
My Berlingo does it, apparently it's supposed to
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Modern diesels have throttle valves in the inlet and gas recirculation systems. In theory it's possible for a Diesel engine to continue running on oil vapours that leak out turbos and what not rather than the fuel injected. So on shut down, you have to stop both the fuel and air, which is where the valves come in. The valves are controlled with pulse width modulation signals (high frequency pulses of voltage). These pwm signals and the valves responding to them is what you are hearing.
The engine will shut the valves close for a period, to ensure the engine is fully stopped and no air getting in, then after a while it'll open them to let vapours clear, then it'll reset to its off position.
Generally modern diesels use the EGR throttle at key-off to give a smoother run down. Otherwise the engine can "bounce off the next compression stroke" at low speed and the crank turns backwards a bit, which all leads to a nasty shake, perceivable in the cabin to the occupants. When you key off old dervs that don't do this it's often really rather noticeable, and Stop Start systems means modern engines are stopping a lot more often. By closing this throttle just before they turn the fuel off, they build a vacuum in the plenum, and so there is nothing to compress, and hence no bounce back event.
Modern diesels all seem to have a post switch-off routine. My sprinter makes a noise a noise a bit like a startled pheasant. Transits do a little kitten sneeze.
Could be the bottom thruttock valve has worn causing fintle rattle.
fisha - Member
Modern diesels have throttle valves in the inlet and gas recirculation
Is that the long winded way to write "dozer valve", Don & Maxtourq ? 😛
All turbo encabulators do this.
Wife's rampant rabbit recharging in glove box?
Love eggs in the glovebox?
Rabbit eggs in the .....
o no wait
It could be the fan - though I wouldn't describe the fan noise as a buzzing noise - it's most definitely a loud fan noise. My SMax has always done this and it is a definite high pitched electronic buzzing noise that is on for about 30 seconds then goes off then comes back on again intermittently with a crisp relay click sound when it switches on and off. I asked about this alot when the car was new (to me) and the dealership, as usual, were about as much use as a slap in the face with a wet fish. I have done frantic googling and querying other self-proclaimed specialists, but still not got a satisfactory answer or explanation. What I have managed to establish is that it is not a fault, is normal, has done it since i've had the car (now 6 years old) so i've just learned to ignored it.
Various suggestions i've had are that it is the climate control vent servo's closing the climate control vents. This is BS as the noise is intermittent and goes on for some time after the car is switched off. If it were the climate control vents it would do it once after engine shut down then not again.
It could be a small pump in the fuel system that manages the very high fuel pressure once the engine is shut off by circulating the fuel around the system to prevent coking of fuel in the hot parts of the system and to maintain fuel pressure while the engine is off so that it starts when you come back to the car to start it - this sounds a bit more plausible as it does happen for a time after the car is switched off and then stops occurring, maybe about an hour or so after shut down, so could happen so long as the fuel in the manifold is at an elevated temperature and stops once it's cooled.
Anyway whatever it is it's not been a problem even if i've left the car on the drive for 2 weeks or so, so doesn't run down the battery or anything.
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My 10yo Mazda Diesel does a wee buzzing thing for about 3-4 mins after turning off, my 2 yo Nissan Van also.
"Could be the bottom thruttock valve has worn causing fintle rattle."
Probably this.
Our petrol Scenic did that, I assume it was related to why the battery would randomly go flat even though at the service it tested okay.
Perchy
Have you checked in the boot?
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My sprinter makes a noise a noise a bit like a startled pheasant.
My diesel used to do a very similar thing, kind of like a crow caught by the nadgers.
My Kangoo did this, it was the electric fuel pump running on.
I think it does it to keep the diesel fuel parts cool after you switch off.
Hamster warming down on the turbo?