Trunk randomly opens.
Thread Starter
Junior Member
Joined: Mar 2010
Posts: 58
Likes: 0
From: Springpatch, IL
2003 Mercedes CLK500
Trunk randomly opens.
Ok, so this question is for my shop because were all stumped and are running out of options. We have a C240 here and the trunk will pop open all on its own, while driving, stopped, sitting outside locked, any time. And conveniently when the trunk opens, the alarm goes off. We changed out the rear SAM with a known good one, unplugged the trunk latch itself, but the relay still clicks telling us its still getting signal. The last thing we can think of is the EIS module but we dont want to change that out unless were sure thats the issue.
Any ideas???
Any ideas???
Super Moderator
Joined: Jun 2008
Posts: 19,942
Likes: 192
From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
These are awful problems to diagnose. It could be the EIS.
Disconnect the drivers door trunk switch & see if this helps. The switches sometimes fail & short/contact intermittently.
Disconnect the battery carefully & reconnect to hard reboot all modules. You will then have to resynch things as per the sticky at the head of the forum.
What year is this C240? Early models had very fragile SAM's so be careful disconnecting the battery. Best way is to change out a battery with a quiescent current device to keep the car powered up but then you can't achieve a reboot of the electronics.
Good luck!
Disconnect the drivers door trunk switch & see if this helps. The switches sometimes fail & short/contact intermittently.
Disconnect the battery carefully & reconnect to hard reboot all modules. You will then have to resynch things as per the sticky at the head of the forum.
What year is this C240? Early models had very fragile SAM's so be careful disconnecting the battery. Best way is to change out a battery with a quiescent current device to keep the car powered up but then you can't achieve a reboot of the electronics.
Good luck!
MBWorld Fanatic!
Joined: Jul 2008
Posts: 8,384
Likes: 800
2019 G70 6MT & 2022 Ford Maverick XL
My car won't open the trunk with the car in motion from the drivers side door button. Wouldn't that rule out the door switch as your problem? Hrm.. this is really tricky and would be highly annoying (and dangerous).
Senior Member
Joined: Jan 2010
Posts: 283
Likes: 2
From: Mississauga, Ont.
2007 C280 4matic Avantgarde
I’m really confused now. I can open my trunk when car is in motion. Have not try on hwy yet 
. I have dodge and trunk will not open if transmission is in any position but P.
. I have dodge and trunk will not open if transmission is in any position but P.
MBWorld Fanatic!
Joined: Jan 2005
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From: Orange County
2005 C Wagon (No snickering please!)
The switch in the key can become dicey after years of use. It can be infused with pocket lint that holds moisture leading to corrosion.
Try taking the battery out of the key to see it the relay still engergizes with the car sitting still. To examine the key you can use a video camera to observe the infrared LED in the end of the key. It it illuminates randomly the key is not working properly. You can also "listen" to the key RF signal with a scanner radio. Different countries have different frequencies, so you need to check the WIS to see where to tune the scanner.
Try taking the battery out of the key to see it the relay still engergizes with the car sitting still. To examine the key you can use a video camera to observe the infrared LED in the end of the key. It it illuminates randomly the key is not working properly. You can also "listen" to the key RF signal with a scanner radio. Different countries have different frequencies, so you need to check the WIS to see where to tune the scanner.
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Super Moderator
Joined: Jun 2008
Posts: 19,942
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
Matt - Correct - The trunk release should lock out when in motion. My car won't. However some cars will open at any time. Damn Benz inconsistency with programming. This can be set with a Star.
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Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
Ok, so this question is for my shop because were all stumped and are running out of options. We have a C240 here and the trunk will pop open all on its own, while driving, stopped, sitting outside locked, any time. And conveniently when the trunk opens, the alarm goes off. We changed out the rear SAM with a known good one, unplugged the trunk latch itself, but the relay still clicks telling us its still getting signal. The last thing we can think of is the EIS module but we dont want to change that out unless were sure thats the issue.
Any ideas???
Any ideas???
Did you fixed this problem? I have same issue on same car. 2002 C240 and trunk will open on its own. Does someone know what's the root of this issue?
Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
I don’t think it’s the driver door control module. If the car is locked the driver side button to open trunk is not operational. In other words if the car is locked I’m not able to open trunk with button on driver side door. Also car alarm is going off if the trunk open itself. I inspected the lock and it looks ok. I think The rear sam send false signal to the lock.
