E-Class Coupe (C238) & Cabrio (A238) 2017 - E200, E220, E300, E350, E400, E450 [Coupes &Cabriolets]

2020 E450 Convertible Alarm Gremlin

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Old Aug 26, 2025 | 08:05 PM
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2020 E450 Cabriolet
2020 E450 Convertible Alarm Gremlin

My W213 convertible shows 13,375 miles on the odometer and looks and runs like a brand new car, just like a 13,000 mile car should. About 3 weeks ago, the alarm went off at 2 am. I turned it off, checked the car, nothing. Since then, the alarm has continued to go off every couple of days at random times of the day, only twice at night and always in my house, never anywhere else. Last week I took the car to the dealership (I have an extended warranty), they kept it from Tuesday until Thursday, ran every diagnostic in the book and found absolutely nothing. Batteries are good, FOB batteries are new, charging system is perfect, all sensors work, no fault codes, etc. The service advisor called me today and said that the shop foreman, who was off last week, would like to check one more thing and gave me an appointment for the day after tomorrow, Thursday, August 28. Does anybody have any ideas?
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Old Aug 26, 2025 | 08:15 PM
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Originally Posted by Copepe
My W213 convertible shows 13,375 miles on the odometer and looks and runs like a brand new car, just like a 13,000 mile car should. About 3 weeks ago, the alarm went off at 2 am. I turned it off, checked the car, nothing. Since then, the alarm has continued to go off every couple of days at random times of the day, only twice at night and always in my house, never anywhere else. Last week I took the car to the dealership (I have an extended warranty), they kept it from Tuesday until Thursday, ran every diagnostic in the book and found absolutely nothing. Batteries are good, FOB batteries are new, charging system is perfect, all sensors work, no fault codes, etc. The service advisor called me today and said that the shop foreman, who was off last week, would like to check one more thing and gave me an appointment for the day after tomorrow, Thursday, August 28. Does anybody have any ideas?
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I wonder if some item is triggering the keyfob panic alarm button in your jacket or bag but why only midnight. Check the spare key as well. Is your cat triggering it? Any other pets? Are they playing with the fob at night? Other possibilities is through Mercedes Me sound and honk feature used to find the car.
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Old Aug 26, 2025 | 08:22 PM
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Thank you for your comments

It only happened twice at night but always in my house. No, the 2 key fobs can't be pressed inadvertently where they are kept. One of the instances when the alarm went off I was walking by the car about 7 to 10 feet from it. There was nothing around, not even a light breeze.
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Old Aug 26, 2025 | 11:14 PM
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From: MBworld
bone stock E55 AMG
moved to A238 forum...
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Old Aug 27, 2025 | 02:47 AM
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Originally Posted by Copepe
It only happened twice at night but always in my house. No, the 2 key fobs can't be pressed inadvertently where they are kept. One of the instances when the alarm went off I was walking by the car about 7 to 10 feet from it. There was nothing around, not even a light breeze.
It is always twice and consistently?
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Old Aug 27, 2025 | 07:05 AM
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Originally Posted by W205C43PFL
It is always twice and consistently?
When I said it's only happened twice at night, I didn't mean the same night. I meant to say that since the issue began it has only happened at night in 2 occasions, the rest has been during the day. Having said that, last night it happened again, so now it's thrice at night.
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Old Aug 27, 2025 | 07:27 AM
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Originally Posted by Copepe
When I said it's only happened twice at night, I didn't mean the same night. I meant to say that since the issue began it has only happened at night in 2 occasions, the rest has been during the day. Having said that, last night it happened again, so now it's thrice at night.
I see that is strange, I wonder if there is some sort of interference.
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Old Aug 27, 2025 | 07:34 AM
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I do too because it has never happened anywhere else other than my house.
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Old Aug 27, 2025 | 07:34 AM
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Originally Posted by Copepe
I do too because it has never happened anywhere else other than my house.
let me think, what systems do you have in your garage by chance?
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Old Aug 27, 2025 | 07:40 AM
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No garage. The car sits on the driveway...as it has since January 2 of this year.
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Old Aug 27, 2025 | 08:58 AM
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Originally Posted by Copepe
No garage. The car sits on the driveway...as it has since January 2 of this year.
Loud noises nearby? I am scratching my head as much as you right now.
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Old Aug 27, 2025 | 09:04 AM
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Loud noises like fireworks for example can make the alarm sound.
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Old Aug 27, 2025 | 09:33 AM
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Nothing that wasn't there during the 7 previous months. Besides, I was 10 feet from the car for one of the events. There was nothing. We live on a 1 way street across from a passive park.
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Old Aug 27, 2025 | 10:15 AM
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Originally Posted by Copepe
Nothing that wasn't there during the 7 previous months. Besides, I was 10 feet from the car for one of the events. There was nothing. We live on a 1 way street across from a passive park.
Another thing I can think of is...
MB is very sensitive to electrical voltage swings, so my question is, is the vehicle 12V battery sufficiently charged to avoid maybe causing a glitch in the system?
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Old Aug 27, 2025 | 10:24 AM
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Originally Posted by W205C43PFL
Another thing I can think of is...
MB is very sensitive to electrical voltage swings, so my question is, is the vehicle 12V battery sufficiently charged to avoid maybe causing a glitch in the system?
According to Mercedes Benz of Cutler Bay and to a Mercedes-only independent mechanic, yes, the battery and the charging system are in perfect state and working per specs.
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Old Aug 27, 2025 | 10:25 AM
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Originally Posted by Copepe
According to Mercedes Benz of Cutler Bay and to a Mercedes-only independent mechanic, yes, the battery and the charging system are in perfect state and working per specs.
I guess I will just go with the not all dealerships are created equal and suggest trying a different MB dealership to see if they can find the issue.
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Old Aug 27, 2025 | 10:36 AM
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I get it, but the independent mechanic concurred.
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Old Aug 27, 2025 | 11:06 AM
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Originally Posted by Copepe
I get it, but the independent mechanic concurred.
I guess now we can just wait for that one more thing they are checking ...
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Old Aug 27, 2025 | 11:45 AM
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I will keep you abreast.
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Old Aug 27, 2025 | 11:51 AM
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Originally Posted by Copepe
I will keep you abreast.
All the best
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Old Aug 27, 2025 | 12:22 PM
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Originally Posted by W205C43PFL
All the best
Thank you
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Old Sep 6, 2025 | 06:49 PM
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Originally Posted by W205C43PFL
All the best
I took the car back on Thursday, August 28. They called on Wednesday, September 3, and told me that they'd dug deep and found that a module in the console showed that the alarm had gone off because the console's clamshell doors were opened, which obviously wasn't true. They checked the clamshell doors "switches" or contacts or whatever, found that one was sending the false reading, replaced it and they held the car until the end of the day on Thursday to make sure the false reading didn't come back. I picked up the car and, so far, it's been fine. However, since they had the car there, I also asked them to replace the battery, which seemed to be fine but my car is a 2020 model year and it had the original factory battery, so who knows.
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Old Sep 6, 2025 | 09:26 PM
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Originally Posted by Copepe
I took the car back on Thursday, August 28. They called on Wednesday, September 3, and told me that they'd dug deep and found that a module in the console showed that the alarm had gone off because the console's clamshell doors were opened, which obviously wasn't true. They checked the clamshell doors "switches" or contacts or whatever, found that one was sending the false reading, replaced it and they held the car until the end of the day on Thursday to make sure the false reading didn't come back. I picked up the car and, so far, it's been fine. However, since they had the car there, I also asked them to replace the battery, which seemed to be fine but my car is a 2020 model year and it had the original factory battery, so who knows.
Thanks for the update OP. I am just glad they found the issue.
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