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Mercedes Key Fob Not Working

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Mercedes-Benz key fob not working? The first thing you need to do is change the keyless remote battery. We assume you have already done that part by now. Is your Mercedes key fob not working after a battery change? This article will help you troubleshoot problems where the Mercedes key fob doesn’t work or no longer unlock/locks doors or trunk. In most cases, the key can start the car but not work as a keyless entry remote. Generally speaking, when Mercedes key fob is not working, it’s because either because the key is defective or the All Activity Module (AAM) is not recognizing the key signal, or it is not receiving signal due to an antenna issue.

If you need a replacement battery note that Mercedes-Benz uses CR2025 battery type.

Common Mercedes Key Fob Problems

  • Mercedes key fob not working after battery change
  • Mercedes remote doesn’t work anymore
  • Keyless remote doesn’t lock/unlock the car
  • Mercedes key fob won’t unlock doors
  • Panic button doesn’t work
  • Trunk unlock doesn’t work

Troubleshooting / Possible Fix

Step 1: Check Remote

Ensure you have new batteries in your key fob. Next, look carefully at your Mercedes-Benz key. When you press the button on your key you should see a small RED led light. The light should light up every time you press any of the buttons (Lock, Unlock, Panic, Trunk).mercedes keyless lock unlock not working

Does the red LED light turn on? 

If the light doesn’t turn on, then you have a bad key fob remote.

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If the light comes on, then continue to the next step.

Step 2: Check Infra-red signal using your phone

Next, we need to check if the remote is sending out a message. The remote emits infrared waves. While you can’t see infrared light with your eyes, there is an easy way to check. Grab your phone and turn on the camera. Point the camera to your phone and carefully see if you notice a light every time you turn you press a button on the remote.

Do you see the infrared light? 

If you don’t see infrared light, then you have a defective key.

If you see the infrared light, then the problem is elsewhere so continue to the next step.

Watch the following video to learn how to test if Mercedes key fob is working properly.

Step 3: Check Central Locking Fuse

Remove the metal key from the keyfob and use it to manually unlock the doors.  Next, you need to check the fuse for the central locking circuit. Not only that but also look at the fuse for the Antenna Module and AAM.  Because your MB receives the lock / unlock signal via the antennas installed on your car, a bad antenna module fuse can also cause Mercedes key fob to stop working. Depending on the MB class, this fuse can be found in one of the fuse boxes located in the engine bay, side of dashboard, under rear seat or trunk. If you find a blown fuse replace it. Always replace blown fuses with the same ampere rating fuse. Don’t use a higher ampere rating than what is recommended.

Step 4: Program / Synchronize Remote

To synchronize a Mercedes-Benz key to your car all you need to do is insert the key into the ignition for a few seconds. This works in most cases but every now and then you may need to follow further instructions to synchronize your Mercedes key fob remote with your car. Even the new keys that are purchased from the dealer should function properly once you insert them into the ignition.

There are a few cases when you need to program your key fob remote to your Mercedes-Benz. Below you will find general instructions on how to synchronize a Mercedes key fob. For model specific instruction check your owner’s manual.

Instructions on how to sync Mercedes remote:

  1. Insert the key into the ignition.
  2. Quickly remove key from ignition and within 10 seconds hold down the lock button.
  3. Continue holding the lock button, and at the same time press, the unlock button five times.
  4. Next release all buttons and press the gate/trunk button one time.
  5. Your Mercedes remote should be synchronized. Test to see if lock / unlock functions are working.

Step 5: Diagnose All Activity Module (AAM)

The last step is to diagnose the AAM module. Now, this is where this repair can get expensive because you either need to go to a mechanic or purchase diagnostic scanners. You will need to start by reading the fault codes from the AAM module. You can accomplish this using a diagnostic scanner such as iCarsoft MB II. Hopefully, you will be able to pinpoint the issue and fix it yourself. If the AAM module is defective or any programming is necessary the iCarsoft MB II scanner won’t be much help other than just reading and clearing codes. You will either need to take your MB to a shop that has MB Star Diagnostic Scanner or has an advanced scanner such as Autel Maxidas or SnapOn Solus.

Mercedes-Benz owners who have the following problems will find this article helpful:

  • Mercedes class key fob not working
  • Mercedes ml key fob not working
  • Mercedes CLK key fob not working
  • Mercedes E C CLS key fob not working
  • Mercedes a160 key fob not working
  • Mercedes C-Class C220 C230 C300 key fob not working
  • Mercedes CLS key fob not working

10 comments

  1. I have a 2007 C 230 and my fob is not unlocking the doors the fob lights up the infrared works as well but the fob will not turn ignition its seem like no signal is being sent or received my battery under the hood was low on volts so i bought a $150.00 battery and still nothing

  2. Hi there, my W204 c-class fob would not lock the car. even though the fob unlock it if I manually lock the 4 doors. Before now, if I remove the silver key from the fob and I use it to unlock the car manually, it begins to sound an alarm, but now it doesn’t sound that alarm anymore. the fob unlocks and opens the trunk, but it just wouldn’t lock the car.

  3. How do I continue to step 3 if my key is not working and I therefore can not get to my fuse box at all or in the car what so ever??

  4. My key fob will unlock car wont start ignition though on opening key fob up a very thin strip of metal smaller than a needle with a plastic xovering has fell out doea anybody know where this has come from

  5. My 03 cl55 amg headlight not bright enough can barely see . Any idea what this problem could be,?

    • The HID bulb may need to be replaced. That’s where I would start. Especially if the bulb is getting ignited properly.

  6. I have a SRT6 Crossfire which shares the R170 platform (SLK32 AMG). The batterys leak in the alarm causing the alarm to go off randomly. One way to shut it off is pull #9 fuse under the hood. But this fuse also disables the key fob.
    So check #9 fuse isn’t bad if your key fob isn’t working. A long with the key fob batterys.

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