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).
Does the red LED light turn on?
If the light doesn’t turn on, then you have a bad key fob remote.
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:
- Insert the key into the ignition.
- Quickly remove key from ignition and within 10 seconds hold down the lock button.
- Continue holding the lock button, and at the same time press, the unlock button five times.
- Next release all buttons and press the gate/trunk button one time.
- 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
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- 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