Post-battery change 'knock'

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RJDriver

New Member
Joined
Aug 18, 2017
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1
Car
CLK240
The car: a 2003 CLK240. I recently had a new battery fitted. Reset the the windows, no need of a new code for the radio - all good. But....after the engine starts, there is a 'knocking' sound coming from somewhere behind centre console. I can only like the knock to one hitting an empty tin can with a pen - but here's the thing, it is alsways 50 'knocks' and then it stops. It is always 50 knocks, never 49 or 51.

Any ideas what's causing it and how to stop it? Needless to say, it has only appeared since the battery was fitted.
 
Knocking from behind the dash is commonly a malfunctioning air distribution flap motor. The system will attempt to reposition the flap a number of times then give up.

Get the codes read using STAR would reveal which motor. It may be the system needs resetting. The flaps in my S203 went 'out of sync' and needed resetting.
 

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