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Discussion Starter · #1 ·
I have recently run into this issue. If I turn off the car, the system is not turning completely off. If I had the AC turned on, the light will still be illuminated after taking the key out, and an audible buzzing sound can be detected until pressing the button and disabling the AC (all while the car is off). The P light on the gear shifter stays illuminated all the time as well, and I thought I remember that turning off after a few moments of powering down. I have no idea what is happening and I really don't want the car to end up bricked. Any ideas? I am at 18800 miles, second owner. It is old enough it is probably not covered under warranty anymore unfortunately.
66284


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Something has to be up.
The a/c goes off as soon as the key is off with the shifter light going off a few seconds after.
Unfortunately both of those are controlled by the Sam unit via data bus if I’m not mistaken.
You may have to pull a battery cable temporarily to see if it helps.
 

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Discussion Starter · #3 ·
the battery was completely drained earlier tonight and I had to jump it. Would it still be worth unplugging completely? I feel it would produce a similar effect.
 

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It would.
I would still try a different battery just in case as these cars do some weird stuff when the battery starts to go bad(trust me I found out the hard way with mine when I got it)
I may be in the key switch unit but not sure.
Most of the parts for these cars can be got easy but depending on what it is will likely need programming with the Mercedes scan tool.(Sam unit definitely would)
You may want to check the grounds in the car and at the battery.
 

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Discussion Starter · #5 ·
Do people obtain their own Mercedes scan tools or will that need a trip to the dealership? Good call on checking a new battery, that might take care of it if we are lucky.
 

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You can get clones of it though they still aren’t cheap and from what I’ve seen requires a computer to work.
You may get lucky at you local Mercedes dealer but I doubt they will loan one out(they will scan the car though)
Yes a weak battery in these cars causes all kinds of weirdness(had mine light the cluster idiot lights up due to a bad battery with the key out which freaked me out when it first did it as I had just been listening to the radio)
I think(it’s been a few months since it did that) that it did keep the shifter light on dim like when it lit up the cluster lights.
I had it recently do the no odometer display due to a failing battery(which was replaced under warranty)
I hope that’s the cause of the issue as it’s sure likely it(battery can develop a bad cell and it will drag the good cells down quick)
Replace the battery and make sure the cables are tight on it and see if it helps.
Good luck.
 

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Discussion Starter · #7 ·
I think you hit the nail on the head. Took the car to O'Reilly's and they said the battery was toast. Put a new one in and everything seems to be working like normal again.
 

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That’s great news.
Remember the car will warn you before the battery goes.
Be glad it did before the battery got you out somewhere and couldn’t or wouldn’t start the car.
Trust me I’ve been there before and it’s not fun.
 
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