W203 Randomly Unlocking and Locking Doors

[Eric Price]

Hello,

This is my first post in the forums although I have been lurking for several weeks. I have a problem on my '06 W203 C-Class (180K saloon) regarding some weird locking issues and I hope that somebody else has had a similar problem to mine and been able to solve it.

When I first purchased the vehicle the remote didn't want to unlock the vehicle. There was no sign of life and so I replaced the battery in the key (I only had one). That was great, I now got a flashing red led on the key but still no unlocking on the car. I then went to check all the fuses and strangely not only was the 7.5 amp fuse for the remote receiver missing but there was also a bag of fuses in the boot with the Mercedes label on it saying 'Lock Kit'. I put the fuse in the slot and hey presto everything is working.

During the past few weeks as I tidy up some little niggles on the vehicle I have thought I have seen it randomly lock and unlock itself. I didn't give this enough attention thinking I had accidentally knocked the key in my pocket.

This evening however I get on a knock on the door from a neighbour saying that the boot/truck is open. I go to investigate and the car is locked. I close the boot, test the locks a few time, give it a quick Google and then sit in the back seat and tap against the rear fuse box, something about a SAM module that can get knocked and cause this to happen but nothing.

I am wondering now if it is a fault with the key I got with the vehicle so I have removed the batteries from it and swapped it with the spare I had made just after I got the car (but never used).

Has anybody got any ideas about this? Maybe this has already been reported elsewhere in these forums but I missed it.

Thanks in advance,
Eric

 

[BillyBoy]

I had something similar in my W220, where the boot popped open when I shut the back door on occasions, then eventually refused to shut, so I had to take the fuse out. It turned out to be a microswitch in the boot lock assembly that detected when it was latched. The garage replaced the microswitch and all was good afterwards. The boot lock on the W220 was a complicated arrangement of switches and pneumatics, and the wrong signals from the sensors played havoc with the locking mechanism.

 

[Eric Price]

Update: I started getting the same issue with the second key and I read in another forum that an owner had found the buttons on their remote were easily pressed when the keys were in their pocket. I recall that the keys had always been in a pocket when the issue could have occurred so I purchased two signal blocker bags for them.

https://smile.amazon.co.uk/gp/product/B078ZJH32B/

It has only been four days since I got them but so far no more issues. I will give it another couple of weeks before I will be sure that they have solved the issue. I never had this problem with my other car (Volvo S40) but I guess the buttons on that remote are more resilient.