jwickert

Hello all,

Yesterday I shut my 2011 C300 4matic Sport off after driving to work and I noticed the key fob wasn't working at all. Couldn't lock/unlock doors, trunk, or start the car again. I took the fob to my mechanic who tested it and said that it was sending out a signal. The indicator lights on the fob do illuminate when you use it. My other fob works just fine. I put a new battery in the first fob and no change. Anyone have any ideas short of me dropping 250 dollars on a new fob?

Jonathan

MacVidMB-V8

You should test both IR and RF portions.

Rare to have both quit at once.

IGB

You can easily check to see if the IR (edited) transmitter is working. Start the camera app on your phone and press buttons on the key while pointing it towards the camera lens. If IR is working, you should see a purplish glow.

It's not a very clear picture but you get the idea. See the purple glow?



Are you sure the battery you put in it is full?

Have you recently dropped it or spilled something on it?

And how did the mechanic test it whereby he was able to establish it was "working"?

MacVidMB-V8

This is not always useful advice.

In fact, it is IR you see if that test works.

RF is "Radio Frequency" and not going to be seen by a camera.

And I can tell you for a fact that my iPhone 7 does not see the glow from either of my working keys.

IGB, which phone are you using?

IGB

I did state RF at first which was a slip... but in the second line, I did state IR

Using a Note-5...

Edited to add: I don't know about an iPhone 7 but on previous models, it used to be that the front camera could see IR

MacVidMB-V8

you're right.

front camera can see, back can not

good catch

jwickert

Hell all and thanks for the responses. My mechanic had a hand-held device for testing fobs. He set it to scan, clicked my fob, and the scanner immediately said RF signal detected. I did take a photo of the fob while clicking a button and both lights showed up. I've also tried the following re-sync sequence:

If your SmartKey isn't working, you might need to re-sync it. The main symptoms are the key won't unlock the doors or start the car. You may see a blinking red light when you press a button.

Insert the key and turn it to the "ON" position, then press and release the lock button on the key.
Press and hold the remote's unlock button.
In 1-2 seconds, press the remote's lock button five times in a row while holding the unlock button.

When doing the re-sync I've tried it rolling the ignition forward 1 and 2 clicks. Hasn't worked yet, but sometimes these cars are finicky. Anything I'm missing in that sequence? If I can't get that to work I'm thinking I'll just have a service dept. order me a new key. I'd hate to drive an our to the dealer for them to troubleshoot it and tell me that I need to order a new key anyways. BTW, I didn't drop the fob or get it wet lately. Over the past few weeks I noticed the fob would need a few clicks to open the trunk and doors. Then when I got to work I took the key out of the ignition and it didn't work. What do you think?

Jonathan

MacVidMB-V8

Please let us know what comes of this.

Might be worth pulling the PCB out of key and getting a pic.

It is rare for BOTH parts of key to quit at once. The starting function is powered by the car through magnets and uses IR. The distant locking and unlocking uses RF and batteries in key. For both to quit at same time is odd.

Most keys I have received for repair had obvious water damage. This appears as white crusty stuff between IC legs or actual green crusty traces on PCB where metal salts get moved by electricity and create new path, killing key.

Sometimes I have been able to fix with a toothbrush and alcohol, removing all traces of these salts. A cracked button is the usual place this water gets in, driver washes hands, doesn't bother with electro dryer, pushes button, a little dirt and moisture gets in, etc.

days

This exact problem happened to my son's 2009 C300. The key FOB's checked out (at least the battery and IR), and I checked the 7.5 amp antennae module fuse, which was normal. I had it towed to a friends shop, who specialize in Mercedes and BMW, and it turned out to be a blown 100 amp fuse, located by the battery. It comes as a module and costs approximately $300 USD to purchase from Mercedes. Takes just a few minutes to replace. I did a lot of searches regarding this problem and there was nowhere that mentioned the 100 amp fuse as a possible fault. I hope this helps someone out who is having the same problem.

John Wu

iphone 4 can see IR, iphone 6 can not see IR, it depend on the lens filter.