colladacool

Hey guys,

I've had my s4 for about 7 months now and almost everything after turning the car off, the fans stay running for what i'd like to say is 1-3 minutes (different everytime). Do you guys also have this happen?
Also, just recently for about 5 minutes before i turned the car off and back on, i had a "audi presense restricted. Restricted sensor vision due to surroundings" message pop up one time, this happened randomly while driving with nothing around me at all. It went away after turning the car off and back on. Does this happen to any of you?

Thanks

markcincinnati

Normal.

The last dozen Audis, maybe more, that I've had did this.

The cause is heat.

It the sensors detect "heat" (I assume radiator heat) above some threshold, the fan stays on (or turns on) until the heat is dissipated.

If the fan doesn't come on or stay on, the reason is that there is insufficient heat to trigger the fan's operation after shut down.

biador619

yea thats typical for vehicles with turbo chargers. turbo chargers pretty much recirculates the exhaust for boost causing more heat in the engine bay. the fan stays on after you turn of the engine to help dissipate that heat.

India Whiskey Charlie

All cars with electric fans do this. My first was a 1978 Ford Fiesta... LOL!

TT-S4

Yes. Turbochargers are driven by the engine's exhaust pressure.

A slight correction if I may, for those who may think that a turbo engine "recirculates" exhaust.

Turbochargers do not "recirculate" exhaust. For the turbo operation, the engine's exhaust drives the turbo and then moves into and out of the exhaust system, and does not recirculate back into the engine.
Engine exhaust is driven into the turbo, in this engine there is a "twin scroll" single turbocharger.
A turbo has two sides/turbines, a hot-intake side and a cold-compressor side. The two sides/turbines are connected and sealed off from each other, and held by a bearing within the larger housing..
Exhaust from both banks of cylinders feeds into and drives the turbo from the hot side, which also spins up the cold intake side.
The cold side compresses fresh air in the intake system.



Hot exhaust side in red.
Cold compressor side in blue.

markcincinnati

Perhaps we could say a car with a turbocharger has the exhaust "redirected" or rerouted so that the above explanation by TT-S4 can happen.

TT-S4

We could say that, if it helps someone to understand how a turbo is driven compared to a normally aspirated engine.
However, in a turbo system, by design, the exhaust is directed into the turbo, not "re-directed".

Perhaps the poster was thinking about the "diverter-recirculator" valve, which is designed to "re-circulate/divert" the already compressed air back into the intake side, when the throttle is closed and the compressed air has to have somewhere to go.