Mercedes-Benz OEM Smart Key Fob – 4C Chip, 315 MHz, HU64 Blade

By Mohammad H. Abdelhadi, ALOA-Certified Master Locksmith, mobile automotive locksmith. Reviewed by Ray Obar, Master Locksmith. Updated June 1, 2026.

Used across a wide range of Mercedes-Benz platforms spanning from the A-Class to the G-Class and several EQ-series electric vehicles, the Mercedes-Benz OEM Smart Key Fob serves as the factory-original proximity key for passive entry and push-button start. Each Mercedes-Benz OEM Smart Key Fob integrates a 4C transponder chip for immobilizer authentication and transmits at 315 MHz for remote keyless entry functions. For automotive locksmiths, this unit presents a layered programming sequence that involves both RF pairing and transponder enrollment through Mercedes proprietary diagnostic protocols. A correctly paired Mercedes-Benz OEM Smart Key Fob enables proximity-based door unlock, trunk release, and engine start authorization via the vehicle’s keyless-go system.

Mercedes-Benz OEM Smart Key Fob: Technical Specifications

The core of this smart key relies on a 4C transponder chip embedded within the fob housing. The 4C chip handles the cryptographic handshake between the key and the vehicle’s immobilizer module, which must verify the transponder’s identity before the engine control unit will authorize ignition. On the wireless side, the fob operates at 315 MHz — the standard North American frequency band for Mercedes-Benz keyless entry systems.

The integrated emergency blade uses the HU64 keyway profile. This blade allows manual access to the driver’s door when the fob battery is depleted or the remote functions are otherwise unavailable. The HU64 is a track-style sidebar key with precise internal milling, and cutting it requires either a code-cut from the vehicle’s key data or impression/decode from the lock cylinder itself. Locksmiths working with the HU64 should note that Mercedes sidebar lock cylinders demand tight tolerances, and even slight deviations in cut depth will prevent the blade from operating the lock.

Validated Vehicle Fitments

The following Mercedes-Benz models and year ranges have been validated as compatible with this fob:

• Mercedes A-Class (2018)
• Mercedes AMG GT (2014–2022)
• Mercedes AMG GT (2015–2020)
• Mercedes AMG GT (2018–2025)
• Mercedes C-Class (2021)
• Mercedes CLE-Class (2024)
• Mercedes E-Class (2023)
• Mercedes EQA-Class (2021)
• Mercedes EQB-Class (2021)
• Mercedes EQC-Class (2019)
• Mercedes EQE-Class (2022)
• Mercedes G-Class (2018)

The spread across both combustion and electric platforms — from the AMG GT performance coupe to the EQA and EQE battery-electric models — reflects a shared keyless-go architecture within the Mercedes-Benz platform strategy. The overlapping AMG GT year ranges in the fitment list correspond to generation updates and mid-cycle refreshes, each of which may carry slightly different module firmware versions even though they accept the same physical fob.

Programming Considerations for Locksmiths

Enrolling a new smart key to any of the above Mercedes-Benz platforms requires access to the vehicle’s Electronic Ignition Switch (EIS) module or its successor, the Electronic Steering Lock (ESL/ELV) module, depending on model year. The 4C transponder within the device must be written with vehicle-specific key data before the immobilizer will recognize it.

Professional-grade diagnostic tools capable of Mercedes key programming — such as the Autel IM608 Pro II with the appropriate Mercedes software license, or the AVDI ABRITES with MN032 — are typically required. The procedure involves reading the EIS/EZS data, calculating key values, writing the transponder, and then performing an on-board key teach-in through the instrument cluster or COMAND system.

One critical step that technicians should not overlook: after programming the fob’s transponder, the RF remote functions need to be synchronized separately. The 315 MHz remote pairing is a distinct process from the immobilizer enrollment. In many Mercedes models, the RF sync is initiated through the diagnostic tool by entering a dedicated key learning mode, then pressing a button sequence on the fob itself.

The HU64 emergency blade should be cut and tested in the driver’s door lock before handing the key off to the vehicle owner. Even though most owners will never use the blade under normal circumstances, verifying mechanical access ensures a complete job and protects against a scenario where the fob battery dies in a parking structure without roadside assistance available.

HU64 Keyway Profile Details

The HU64 is a high-security sidebar keyway used across numerous Mercedes-Benz models. It features internal track cuts on both sides of the blade, with the sidebar mechanism acting as a secondary locking element independent of the wafer tumblers. Duplicating this blade from a working original requires a tracer-guided key machine with the correct HU64 jaw set, while code-cutting from BSNI or EIS data demands an electronic key machine with Mercedes code tables loaded.

Aftermarket blank availability for the HU64 profile is generally good, but quality varies significantly between suppliers. OEM-spec blanks from reputable manufacturers will have the correct nickel-silver alloy and precise dimensional tolerances. Budget blanks sometimes exhibit slight width or thickness deviations that can cause binding in the sidebar mechanism, particularly in newer-production lock cylinders with tighter manufacturing standards.

OEM vs. Aftermarket Considerations for Vehicle Owners

Vehicle owners seeking a replacement for this smart key face a choice between OEM-sourced units and aftermarket alternatives. The OEM fob guarantees exact compatibility with the vehicle’s hardware and firmware, eliminates the risk of housing fit issues around the emergency blade slot, and meets Mercedes-Benz’s original specifications for RF power output and transponder response timing.

Aftermarket smart key shells paired with a separately sourced 4C transponder board can reduce cost, but introduce variables: housing quality, antenna coil alignment, and button membrane durability all differ across manufacturers. For the AMG GT, G-Class, and newer EQ-series vehicles, where replacement key costs from the dealer can be substantial, an aftermarket alternative programmed by a qualified locksmith represents a practical middle ground — provided the locksmith verifies transponder compatibility before beginning the programming procedure.

Regardless of the sourcing path, the programming step itself requires specialized equipment and expertise. This is not a DIY-programmable key. Vehicle owners should expect to engage either a Mercedes-Benz dealership or an automotive locksmith with Mercedes-specific tooling and training.

Battery and Maintenance

The fob uses a coin-cell battery — typically a CR2025 or CR2032 depending on the specific housing revision — to power its 315 MHz transmitter and proximity detection circuit. When the battery voltage drops below operational threshold, the vehicle’s instrument cluster will display a key battery warning. Even with a depleted battery, the 4C transponder inside the device is passive and will still respond to the immobilizer’s interrogation field at close range, allowing engine start by holding the fob directly against the steering column or start button.

Replacing the battery involves prying apart the fob housing along its seam — a task that benefits from a plastic trim tool to avoid scratching the housing. After battery replacement, the fob should not require re-programming; the RF pairing and transponder data are stored in non-volatile memory.

Related help: car key replacement, car key programming.

Compatible and related keys: Mercedes-Benz OEM 4-Button Smart Key Fob, related key: Mercedes-Benz Transponder Key (chip 4A).