Honda OEM 4-Button Smart Key Fob (FCC ID KR5V21) – Key Details

Used across select Acura platforms including the ILX, RDX, and TLX (2015–2020), the Honda OEM 4 Button Smart Key Fob 4-Button Smart Key Fob (FCC ID KR5V21) serves as the factory proximity remote for passive entry and push-button start systems. Each Honda OEM 4-Button Smart Key Fob (FCC ID KR5V21) integrates an ID47 transponder chip for immobilizer authentication, transmitting on a 315 MHz carrier frequency to communicate with the vehicle’s Body Control Module. For technicians, the fob presents specific registration steps that differ slightly between the Acura models it covers. Owners looking to replace the device after loss or damage should be aware that a correctly programmed Honda OEM 4-Button Smart Key Fob (FCC ID KR5V21) must pass both the RF handshake and the cryptographic challenge from the immobilizer before the engine will crank.

Technical Specifications of the Honda OEM 4-Button Smart Key Fob (FCC ID KR5V21)

The FCC ID KR5V21 designates a specific four-button smart key configuration manufactured under Honda car keys & fobs‘s OEM specifications. The four buttons typically correspond to lock, unlock, trunk release, and panic functions. Operating at 315 MHz, this remote falls within the standard frequency allocation used by Honda 4-Button Keyless Entry Remote (MLBHLIK6) | Low Rate Lo and Acura vehicles sold in the North American market. The ID47 transponder chip embedded inside the fob handles the rolling-code cryptographic exchange required by the immobilizer system — without a valid ID47 handshake, the vehicle’s Engine Control Unit will refuse to authorize ignition.

Unlike older Honda remotes that used separate transponder keys and standalone key fobs, this unit combines both functions into a single proximity device. The integrated emergency key blade (housed inside the fob body) allows mechanical access to the driver’s door in the event of a dead battery, though it does not bypass the electronic immobilizer. Technicians should note that battery replacement on the KR5V21 typically requires a small flathead screwdriver or coin to separate the case halves, exposing the CR2032 cell inside.

Vehicle Compatibility and Fitment Details

Based on validated fitment data, the KR5V21 is confirmed to work with the following Acura models:

• Acura ILX — compact sport sedan equipped with Honda’s smart key passive entry system
• Acura RDX — compact luxury crossover SUV utilizing proximity-based keyless access
• Acura TLX (2015–2020) — midsize luxury sedan spanning the first generation of the TLX nameplate

All three models share underlying Honda platform architecture, which explains the common FCC ID across what might appear to be distinct vehicles. The smart key protocol and immobilizer handshake are functionally identical across these fitments, though menu-level feature availability (e.g., remote engine start integration) may vary by trim level and model year.

Programming Considerations for Locksmiths

Registering the Honda OEM 4-Button Smart Key Fob (FCC ID KR5V21) to any of the supported Acura models requires a diagnostic scan tool capable of accessing Honda’s immobilizer subsystem. The ID47 transponder chip uses an AES-based encryption scheme, meaning the fob cannot be cloned through simple transponder duplication methods that worked on older Honda fixed-code chips. Instead, the programming tool must initiate a seed-key exchange with the vehicle’s immobilizer ECU to register the new device into the approved key table.

Most professional-grade automotive locksmith platforms — including widely used tools from established diagnostic manufacturers — support KR5V21 registration on these Acura models. The typical workflow involves connecting to the OBD-II port, navigating to the immobilizer module, reading the current key count, and then following the on-screen prompts to add a new smart key. Depending on the tool and whether existing keys are present, the procedure may require all registered fobs to be on hand during the enrollment session, as some platforms re-register the entire key set simultaneously.

A few technical points worth noting for field work:

• The 2015–2020 TLX and the RDX share nearly identical programming flows, but the ILX can occasionally present different menu paths depending on the tool firmware version.
• If the vehicle battery has been disconnected for an extended period, the BCM may require a brief relearn period before accepting new proximity key registrations.
• The emergency key blade profile is shared across the supported Acura models, so a single blade cut will mechanically fit all three vehicles when the fob is assigned to that VIN.

OEM vs. Aftermarket Considerations

Because this is an OEM-specification product carrying Honda’s factory part designation and the registered FCC ID KR5V21, it meets the original equipment standards for RF output power, transponder response timing, and encryption protocol compliance. Aftermarket alternatives with the same FCC ID do exist in the supply chain, and while many function identically after programming, build quality of the case, button membrane durability, and battery contact reliability can vary between manufacturers.

For vehicle owners, the practical difference between a genuine Honda OEM fob and a quality aftermarket clone often comes down to long-term reliability. The OEM unit typically features tighter case tolerances, a factory-quality rubber button pad, and consistent transponder performance over thousands of lock-unlock cycles. Aftermarket units may save on upfront cost but occasionally require earlier battery replacement or exhibit reduced RF range compared to the original.

Locksmiths advising their customers should weigh the client’s budget against these durability factors. The programming procedure itself is identical regardless of whether the fob is OEM or aftermarket — the ID47 chip and 315 MHz transmitter must pass the same cryptographic enrollment either way.

When to Contact a Professional Locksmith

While battery replacement on the KR5V21 is a straightforward owner-level task, programming and registration require professional equipment and training. Dealership service departments can perform the registration, but independent automotive locksmiths frequently offer faster turnaround and on-site service — particularly valuable when the fob is the only key available and the vehicle cannot be driven to a dealer. A qualified locksmith with the appropriate scan tool can register the device at the vehicle’s location, verify full functionality of all four buttons, and confirm the immobilizer handshake before leaving the job site.