How to Identify Mercedes FBS3 vs. FBS4 Before Key Programming Using Autel?

When it comes to Mercedes-Benz key programming, knowing which immobilizer system you are dealing with—FBS3 or FBS4—is critical.

FBS3 and FBS4 are not interchangeable, and your diagnostic or programming tool must support the specific system in the vehicle.



How to know if your Mercedes Benz is FBS3 or FBS4 before programming keys with Autel IM508/IM608?



Step 1: Connect to the Vehicle

To begin, establish a connection between your Autel MaxiIM device and the vehicle.

Connect your Autel IM608 or IM508 to the vehicle’s OBDII port.

Ensure the device is powered on and communication is established.



Step 2: Navigate to the Mercedes-Benz Immobilizer Menu

Once connected:

On the Autel home screen, go to IMMO (Immobilizer functions).

Select Mercedes-Benz from the list of manufacturers.




Step 3: Select Automatic Detection (VIN Method)

Instead of diving straight into key programming, we use the VIN to identify the system:

Choose Automatic Selection (or a similar option that allows VIN input).

The tool will prompt you to enter the vehicle’s 17-digit VIN.



Step 4: Input the VIN

Enter the VIN carefully using the on-screen keypad. Once entered, confirm and press Enter.

The Autel tool will analyze the VIN and return one of two critical pieces of information:

Scenario A: FBS3 Detected

The screen will display information indicating the vehicle is equipped with FBS3.

It may also show the chassis/system number, confirming the generation.

Outcome: You can proceed with key programming using the FBS3 protocol.





Scenario B: FBS4 Detected

The screen will display the FBS4 status.

Important: As shown in the demonstration, the tool may explicitly state: “Currently this model is not supported by FBS4.”

Outcome: If the tool indicates the model is not supported for FBS4, there is no way to successfully program a key for that specific vehicle using this method.







We can also tell FBS3 or FBS4 from the key.

We can also determine whether it is an FBS3 or FBS4 key from this part of the key. Here is a string of numbers.

With a letter “K” means it’s a smart key, without “K” means semi-smart key.



3 numbers before this space indicate it’s an FBS3.5 semi-smart key.



4 numbers before this space indicate an FBS4 semi-smart key.



“K” at the beginning means it’s an FBS3 full keyless smart key.


“K” in the middle means FBS4 full keyless smart key.