How do I unlock car doors while vehicle battery is flat?

Do they work with the key fob, do you have one of those? They lock when put into gear an unlock when put into park because the BCM - body control module does that .

Door Lock System Components
The power door lock system consists of the following components:
• Driver door lock switch
• Front Passenger door lock switch
• Body Control Module (BCM)
• Relays: Driver Door Unlock -- on vehicles with RFA, Door Unlock, and Door Lock
• Door Lock fuse 15A
Door Lock System Controls
The power door lock system can be controlled by any of the following:
• A power door lock switch activation
• A keyless entry command -- if equipped with keyless entry


Driver and Passenger Door Lock Operation
When any of the door lock switches is pressed to the lock position, the BCM door lock/unlock signal circuit changes from an idle voltage of ~3.4 volts to 0.0 volts generating a lock command. The BCM then applies battery positive voltage to the Door Lock Relay, which in turn applies battery positive voltage to the Door Lock Actuator lock circuit of all the Door Lock Actuators. Since the Door Lock Actuator unlock circuits are held to ground through the resting Door Unlock Relay(s), the actuators execute the lock command, locking the doors.
The lock function can also be accomplished by the BCM having received a keyless entry door lock command, if the vehicle is equipped with keyless entry.


Driver and Passenger Door Unlock Operation

When any of the door lock switches is pressed to the unlock position, the BCM door lock/unlock signal circuit changes from an idle voltage of ~3.4 volts to ~1.7 volts generating an unlock command. The BCM then applies battery positive voltage to the Door Unlock Relay and the Driver Door Unlock Relay when equipped with keyless entry, the relay(s) in turn apply battery positive voltage to the Door Lock Actuator unlock circuit of all the Door Lock Actuators. Since the Door Lock Actuator lock circuits are held to ground through the resting Door Lock Relay, the actuators execute the unlock command, unlocking the doors.
The unlock function can also be accomplished by the BCM having received a keyless entry door unlock command, if the vehicle is equipped with keyless entry. Keyless entry personalization allows the driver door to be unlocked individually before unlocking the passenger doors. When this feature is active, the BCM will require a repeated unlock command to unlock the passenger doors.


Automatic Door Lock/Unlock
The automatic door lock/unlock function is a Vehicle Personalization feature with the following four programmable modes of operation:
The automatic door lock feature is disabled.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON, and all of the doors Unlock when the vehicle is shifted into Park.
All of the doors lock when the vehicle is shifted out of Park with the ignition ON, and only the driver door Unlocks when the vehicle is shifted into Park.
For information on programming the automatic door locks, refer to Vehicle Personalization in Personalization.

Try locking the car using the key in door. Then unlocking. This has worked on a number of vehicles especially if the battery has been allowed to go flat. Eg pagero wouldnt jump start until door locked then unlocked.

put key in ignition turn to number 2 and press the fob buttons open close etc. see if that reset system. also if you charged the batter while on the vehicle you can only charge them with a tried and tested charger from mercedes as you can damage the engine management unit and the voltage control module fitted to the vehicle. failing that you will need to remove the negative lead on battery and leave off for an hour or so. and reconnect, the alarm will still go off until its internal battery goes flat ruf 30min or so. when reconnecting battery make sure the doors are all unlocked and boot is unlocked, you also will need the code for the radio and other units that can be in the vehicle from manufacture. if this does not work then you may need another unit to replace before the engine will start again as it has been damaged. when battery connected sit in the vehicle and turn ignition to number 2 and press fob to lock unlock doors then try to start engine if all goes well the engine and alam will not be a problem anymore

battery may be flat in the fob or the vehicle has forgotten the code for the fob. and will need resetting. change the battery use the key to open the door put key in the ignition. ( fob Ir old type leave fob off the key) turn to number 2 and press fob till doors lock and unlock. then its reset. dont be worried if the alarm goes off while doing this it will go off when the code is restored. if you have 2 fobs you will need to rest that one to.

why not get into the passenger side and open the hood that way.have your battery and charging system checked and repaired. then get the door mechanism repaired so you can use the key

Hi Lara, have you tried unlocking your vehicle by inserting the key in the drivers door lock and turning? If it will not turn try the passengers door lock.

No not if its dead flat, that why you have a Steele key that unclips out of your electronic key to unlock the car to replace the vehicle battery.

Go to http://www.hmaservice.com/ and register (vehicle by VIN). Afterward, you'll have access to technical information (manuals, wiring diagrams, service bulletins, etc) about your vehicle. Unfortunately, you'll find the system which controls the door locks is the ETACS Module (which also controls many other circuits which would become disabled if you pulled its fuse).
I've run into the problem you describe. Frequently it turned out to be a bad switch in the driver's door lock/unlock actuator.... Unless I diagnose the problem myself (or some other qualified technician does it), it could be something else entirely.

U can get in by using a tool called a "slim jim"

I'd like to come into contact with to purchase your vehicle