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Remote may not work if battery voltage is too low or key fob battery is low or key fob is damaged
there is a red dot blinking when any button is depressed on the key fob (keyless entry transmitter)
Can you operate any of the buttons and observe if red light is flashing
make sure battery is charged and point your key to left door handle Infra red receiver, vehicle should unlock, this will pint to key battery problem.
if battery is disconnected but you can still hear chirping noise, then the Alarm horn was activated. it is located under wheel well cover behind passenger front wheel
the low chirping noise is explained as internal Alarm Horm battery is exhausted and has low charge, this one cannot be repaired and has to be replaced.
The signals for the radio remote-controlled central locking system are demodulated and digitized by amplifier module 1, window antenna (A2/71).The data prepared thus are sent over a separate data line to the electronic ignition switch control module (N73) and forwarded there to the CAN interior (CAN-B).During demodulation, the useful signal is separated from the high-frequency carrier frequency (transmitter frequency).
Mercedes Star dignostic Scan tool is used to monitor key signal, but I suggest you check if keyfob light is blinking when you press any key, if not replace keyfob battery first.
Please Check and Let me know