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Premium Member 2012 SLK350
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752 Posts
Discussion Starter · #1 ·
I've done a search with negative results.
I have used my key fob with the red triangle panic button for years. Recently the battery died, so I started using my back up key fob that has the red circle panic button, didn't notice the difference at the time. I have been using the back up fob for months with no problems. Today, I finally got around to replacing the cr2025 battery in my red triangle key fob, but now it doesn't work at all. The only sign of life in that fab is a small flash of red light below the red triangle.

Any thoughts on why it won't work?

:crying:
 

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*Premium Member
2007 SLK55 AMG
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146 Posts
If you look directly into the Infra Red window at the end of the key (the bit that goes into the hole in the dashboard) through your phones camera, can you see it blinking when you press the lock or unlock buttons?
 

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*Premium Member
2006 SLK55 AMG
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415 Posts
When you say "doesn't work" do you mean it won't start the car or that the remote function's won't work?

Note that the battery in the key fob has no affect on starting the car.
 

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*Registered
2005 SLK350
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174 Posts
Have you double checked the polarity of the batteries? Try putting in another set and see what happens. Could be the "new" set that you put in weren't as fresh as you thought.
 

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Registered 2005 SLK 350
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31 Posts
I have the same problem with one of my FOBs for my 2005. It wasn't working so I changed the battery and now it will only start the car. It won't unlock or lock it. Tried three sets of batteries and ended up with the same result. I wanted two keys so I bought a new one at the local dealer to the tune of $250.
 

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*Premium Member
2019 SLC300
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2,862 Posts
!If you can no longer lock or unlock the vehicle with the SmartKey, the batteries in the SmartKey are discharged, the SmartKey is malfunctioning, or the vehicle battery is drained.
 Check the batteries in the SmartKey and replace them if necessary ( page 391).  Use the mechanical key to unlock the driver’s door ( page 387) and the trunk ( page 388).  Use the mechanical key to lock the vehicle ( page 388).  Have the vehicle battery and the battery connections checked ( page 415). If the SmartKey is malfunctioning, contact Roadside Assistance or an authorized Mercedes-Benz Center. iWithout the antenna on the left rear side of the vehicle installed, the SmartKey signaling range is considerably reduced. Hold the SmartKey in close proximity towards the antenna base when locking or unlocking the vehicle.
iYou can also open and close the retractable hardtop using the SmartKey* ( page 244).
iUSA only:
This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions:
(1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.
Any unauthorized modification to this device could void the user’s authority to operate the equipment.
iCanada only:
This device complies with RSS-210 of Industry Canada. Operation is subject to the following two conditions:
(1) This device may not cause interference, and (2) this device must accept any interference received, including interference that may cause undesired operation of the device.
Any unauthorized modification to this device could void the user’s authority to operate the equipment.

Or possible try this.

Restoring to factory setting  Press and hold buttons lock and un-lock simultaneously for about 5 seconds until battery check lamp (page 94) flashes twice.
 

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We used to have a Vauxhall Vectra back in the day , to re code the key put it in the ignition , turn on , don't start the engine , press the lock then the un lock buttons , might be worth a try ???
 

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*Premium Member
2007 SLK55 AMG
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146 Posts
We used to have a Vauxhall Vectra back in the day , to re code the key put it in the ignition , turn on , don't start the engine , press the lock then the un lock buttons , might be worth a try ???
R171 keys aren't that generic. They have to be coded by Mercedes-Benz. Dealers can't do it. You will need to give the dealer your VIN and proof of ownership, they can then request a replacement from MB.

Sent from my 0PJA10 using Tapatalk
 

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Premium Member 2012 SLK350
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752 Posts
Discussion Starter · #16 ·
I have read the owners manual and it does not address what to do when the replacement battery doesn't work.

I called the dealership and they said to bring it down and have the mechanic look at it.

Really? When I asked if this is normal for the fob to not sync when new batteries were put it in, they did not have an answer.

What gives?
 
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