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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4317
Experience:  Mercedes Benz Qualified Diagnostic Technician
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Paul, Same problem with W209 500 - Replaced fob batteries

Customer Question

Same problem with W209 500 - Replaced fob batteries in both keys, no action. I tried to get into the car using the wee metal pull-out key but was afraid it might break in the lock. So can't get into car by doors or by boot. Essentially, b***ered.
Submitted: 4 years ago.
Category: Mercedes
Expert:  Shantal-Mod replied 4 years ago.

Hello Bob,

I've been working hard to find a Professional to assist you with your question, but sometimes finding the right Professional can take a little longer than expected.

I wonder whether you're ok with continuing to wait for an answer. If you are, please let me know and I will continue my search. If not, feel free to let me know and I will cancel this question for you.

Thank you,


Expert:  MB Paul replied 4 years ago.
Hi Bob,

Sorry for any delay in you getting an answer - I am not online much at the moment due to Christmas family comittments but will try to assist!

First of all try aiming the key directly at the drivers door handle at short range - as well as the long range radio signal there is also a short range infra red signal sent to a reciever in the drivers door lock. Sometimes if the radio signal stops working this may still operate the central locking. (if the system has failed completely or the car battery is flat then this will still not work however but is worth trying)

The metal key in the mechanical door locks is the only way into the car without breaking entry - due to the fact that they are almost never used it is not unusual for these to seize up however which sounds like what has happened in your case. Depending on how seized the lock is you can sometimes free them off by spraying some WD40 or similar lubricant into the lock & working the key in & out while trying to turn. A pair of pliers on the key blade helps when doing this. Do not use too much force but spend a bit of time just keep tring to move the key - you may get lucky & free it off.

I have also got entry into cars by sliding welding wire in through the window and hooking the door handle to open it - you will need some plastic trim tools to prise the window away from the body & be careful not to break the glass! Also using some cardboard as a guard to prevent damage to the body, seals or glass when you slide the wire in. Personally I would recommend leaving this to a professional to avoid damage!

Let me know if you need anything else - I may not be around much but will try to reply as soon as I can

Best regards, Paul
Customer: replied 4 years ago.

Hi Paul, and Happy Christmas.

I couldn't wait for your reply so I tried the WD40 trick in both door and boot prior to your reply - without success.

Then I got a neighbour who is an auto mechanic to try - I suspect the WD40 had been working cos he got the boot lock to work (but not the door). Neither have ever been tested before so I guess they had seized.

Fortunately the mechanic is in his early 20s and was able to crawl in and open the door from inside..

Opening the bonnet was a different challenge, sorted by bashing the stuch side of the bonnet front with the flat of a hand while operating the lever from inside the car. This was followed up by more WD40 and lashings of graphite grease.

I have subsequently put the battery on charge, charged up a spare battery, and a booster yellow box. Tomorrow I'll see if anything will work to start the engine (it's pretty cold and I'll maybe wait for some heat in the air as I've got a few days off and don't need the car.

I'll let you know of progress as and when.

Thanks again,


Expert:  MB Paul replied 4 years ago.
Hi Bob,

its quite a common problem with the locks seizing up.

hopefully when the battery is charged all will be good again!

let me know if you need anything else

Best regards, Paul