Have Mercedes Questions? Ask a Mechanic for Answers ASAP
1st thing to check that if the main battery in the car is up to charge and holding at least 12V during cranking
if its not then try charging it up or possibly consider replacement if its over 5 years old
if this is OK then try a vehicle reset, where you remove the battery cables and secure them together for 10 mins to discharge all the capacitors around the car
and then when you reconnect the battery , ensure that the keys are in your hand as the alarm may go off
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