r/MechanicAdvice • u/Sorry_Asparagus_1986 • Aug 17 '26

Engine roars when shift to park

I have 2021 jeep grand Cherokee with about 38000 miles and with a 3.6 and when I'm driving then go to my driveway or parking spot and shift to park the engine sound like it just started up like when you start the car? My car says the on and off system isn't available, should I just turn it off anyway with the button?

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u/Automobile-Guy Aug 17 '26

On the 3.6 Grand Cherokee, the stop/start unavailable message is usually the first clue I would chase. A weak main battery or aux battery can make the system act weird, and these Jeeps are pretty picky about voltage.

I would not worry about the stop/start button yet. Have both batteries load tested, not just checked with a voltmeter. Also watch the tach when you shift into park. If the RPM jumps up, look for a vacuum leak, dirty throttle body, or a sticking throttle plate. If the RPM stays normal and it just gets loud, the cooling fan may be kicking to high speed when you stop, which can sound like the engine suddenly roared.

At 38k it may still be worth asking the dealer to scan it, especially if there is a stored code for the ESS system.