Add Second Smart Key to BYD Sealion 5 DM-i via LAUNCH X431 IMMO Plus

Published: May 26, 2026

If you own a BYD Sealion 5 DM-i and need a spare smart key, the LAUNCH X431 IMMO Plus offers a powerful DIY alternative to an expensive dealership visit. Adding a second smart key to your BYD Sealion 5 DM-i via LAUNCH X431 IMMO Plus is a realistic weekend project for anyone comfortable using professional diagnostic tools. The entire procedure—from PIN retrieval to remote synchronization—typically takes between 15 and 30 minutes, and it can save you 50 to 70 percent compared to what a dealer would charge. Before you begin, you will need the tool, a compatible blank key, and a small number of online credits to unlock the required immobilizer functions.

Understanding the Challenge: Why a Second Key Isn't a Simple Errand

Modern vehicles, especially plug-in hybrids like the Sealion 5 DM-i, use sophisticated security systems to prevent theft. This makes adding a key far more complex than just cutting a blade.

• The Economics of a Spare Key: Losing your only key or simply wanting a backup for a spouse or emergency can be costly. A dealership will typically charge between $150 and $300 for a new smart key, and you often have to book days or weeks in advance. The DIY route with a LAUNCH X431 IMMO Plus brings the cost down to roughly $50 to $80 — the price of a blank key plus online credits.
• Advanced Security Protocols: BYD uses an immobilizer system built around the Body Control Module (BCM). This system does not accept just any key fob. It requires a unique cryptographic handshake, protected by a vehicle-specific PIN code. Without this PIN, the car will refuse to recognize the new key.
• The Right Tool Matters: You cannot do this with a generic OBD2 code reader. You specifically need the LAUNCH X431 IMMO Plus software package loaded on a compatible tablet (such as the Pad VII or X431 V+). The standard diagnostic software on the tablet will not include the key programming or PIN retrieval functions.

Prerequisites: Everything You Need Before You Start

Failing to prepare is preparing to fail. Before you connect the scanner, gather the following hardware and software components.

Hardware Checklist

Software & Account Setup

Your LAUNCH tablet needs to be ready for the job. This goes beyond just having the app installed.

1. Register and Subscribe: Make sure your LAUNCH device is registered with an active IMMO Plus subscription. Without this, the key programming menu will not appear.
2. Purchase Online Credits: This is a critical step that many first-timers miss. The BYD PIN retrieval function requires a server-side calculation. You will need to buy 1 to 2 credits from the LAUNCH online store or through your tool dealer. These credits are consumed each time you request a PIN.
3. Stable Wi-Fi Connection: The IMMO Plus tool communicates with the LAUNCH cloud server to decrypt the security code. A weak or intermittent connection can cause the PIN retrieval to fail, wasting a credit.

How to Add a Second Smart Key to BYD Sealion 5 DM-i via LAUNCH X431 IMMO Plus

This section walks you through the programming procedure. Perform each step carefully and do not rush.

Step 1: Connect and Identify the Vehicle

1. Locate the OBD-II port under the driver's side dashboard. Plug the LAUNCH X431 main cable into this port.
2. Connect the other end of the cable to the diagnostic tablet.
3. Turn the ignition ON by pressing the Start button once without touching the brake pedal. This powers up the BCM without starting the engine.
4. Launch the IMMO Plus application on the tablet.
5. Select "BYD" from the manufacturer list, then choose "Sealion 5 DM-i" from the model menu. If your tool supports auto-VIN detection, let it scan the vehicle automatically.

Step 2: Retrieve the Immobilizer PIN Code

This is the most technically demanding step. The tool must read the BCM and request a decryption code from the LAUNCH server.

1. From the main IMMO Plus menu, navigate to "Special Functions" and select "Read Security Code" or "Read PIN" .
2. The tool will begin communicating with the BCM. Do not disconnect or turn off the ignition during this process.
3. If the automatic read fails, the tool will prompt you to enter the Vehicle Identification Number (VIN) manually. Type the full 17-character VIN exactly as it appears on the dashboard or driver's door sticker.
4. Once the server processes the request, the screen will display a 4-digit or 6-digit Security Code (PIN) .
5. Write this PIN down on a piece of paper immediately. You may need it again if the tool times out during the next stage.

Step 3: Execute the Add Key Function

With the PIN secured, you can now instruct the BCM to accept a new key.

1. Go to "Special Functions" → "Key Programming" → "Add Key" .
2. The system will display the current number of learned keys. A pop-up will ask you to confirm the total number of keys you want the car to recognize after the procedure. Select "Two Keys" (your original plus the new one).
3. Place the original working master key in the designated reader zone. On most BYD models, this is the cup holder at the front of the center console. Follow the on-screen instruction to confirm the key is detected.
4. The tool will then ask you to place the new blank smart key in the same cup holder zone. Hold it there until the screen confirms detection.
5. The tool will now communicate the learned key data to the BCM and write the new key information. This takes about 30 to 60 seconds.

Step 4: Synchronize the Remote Control Functions

In many BYD models, programming the immobilizer chip (which allows the engine to start) is a separate process from programming the remote buttons (lock, unlock, trunk release).

1. Look for a sub-menu labeled "Remote Control Sync" or "RKE Programming" within the key programming section.
2. Select this function. The tool will instruct you to press and hold either the "Lock" or "Unlock" button on the new remote for approximately 3 seconds.
3. Release the button. The vehicle's hazard lights should flash once to confirm the radio frequency signal is synchronized.
4. Test both the lock and unlock functions on the new remote while standing next to the car.

Step 5: Verify and Finalize

This is the moment of truth. You need to confirm that both the remote and the immobilizer are working correctly.

1. Disconnect the LAUNCH X431 scanner from the OBD port.
2. Exit the vehicle and close all doors.
3. Test 1 — Remote Range: Press the lock button on the new key fob. The doors should lock, and the side mirrors should fold (if your vehicle has this feature). Press unlock and confirm the doors open.
4. Test 2 — Keyless Entry: Walk up to the driver's door with the new key in your pocket. Touch the door handle sensor. The door should unlock.
5. Test 3 — Engine Start: Enter the vehicle with the new key. Press the brake pedal and press the Start button. The engine should start without any "Key Not Detected" warning on the dashboard.

If all three tests pass, congratulations — you have successfully added a second smart key to your BYD Sealion 5 DM-i using the LAUNCH X431 IMMO Plus.

Troubleshooting Common Failures

Even experienced technicians encounter problems during key programming. Here are the most frequent issues and how to resolve them.

"Communication Error" with IMMO Plus

• Cause: A loose OBD connection or low battery voltage.
• Fix: Verify the OBD cable is fully seated in both the vehicle port and the tablet. Reboot the tablet and the vehicle. Most importantly, connect your 12V battery charger. The BCM is sensitive to voltage drops, and anything below 12.5V during the handshake can cause a communication failure.

"Incorrect PIN" or "PIN Retrieval Failed"

• Cause: This is the most common complaint when programming newer BYD models. Generic or universal PIN codes almost never work.
• Fix: You must purchase specific LAUNCH credits from the official store. Do not attempt to use a PIN from a different vehicle. Double-check the VIN entry — ensure there are no spaces and that all characters match the vehicle's sticker exactly.

New Key Starts the Engine but Remote Buttons Don't Work

• Cause: The immobilizer chip was learned successfully, but the radio frequency (RF) sync for the remote buttons failed.
• Action: Reconnect the LAUNCH tool and navigate directly to the "Remote Control Sync" function. Skip the PIN retrieval and key learning steps. During this procedure, hold the new key very close to the Start button inside the vehicle before pressing the lock button.

Original Key Stops Working After Programming

• Cause: You accidentally selected "Delete All Keys" instead of "Add Key" from the menu. This erases all existing key data from the BCM.
• Action: Do not panic. This is recoverable. Run the entire "Add Key" procedure again, but this time you must learn both the original key and the new key together in the same cycle. The tool will prompt you to learn each key sequentially.

Topical Depth: Understanding the "Relay Model" of BYD Immobilizers

Why is the battery charger so critical? Why does it need an internet connection? The answer lies in how the BYD immobilizer actually works.

The Sealion 5 DM-i does not use a standard CAN-bus system where keys are stored directly in the BCM. Instead, it uses a "Relay Model" . When you initiate key programming, the IMMO Plus tool reads a "seed key" from the BCM. This seed key is then encrypted and sent to the LAUNCH cloud server. The server holds the cryptographic algorithms needed to calculate the correct response. It sends this response back to the tool, which then relays it to the BCM.

If the battery voltage dips even slightly during this exchange, the BCM enters a low-power protection state and rejects the cryptographic handshake. This is exactly why a stable power supply is non-negotiable. It also explains why you cannot perform this procedure offline — the server must authorize every single key write.

Comparing Dealer vs. DIY: Cost, Time, and Convenience

To help you make an informed decision, here is a direct comparison of the two approaches.

Related Posts

• How to Clone a BYD Dolphin Transponder Chip with LAUNCH X431 X-PROG3
• How to Program a Keyless Entry Remote for BYD Han DM Using LAUNCH X431 Key Programmer
• How to Read PIN Code of BYD Yuan Plus EV Using LAUNCH X431 IMMO Elite
• How to Connect LAUNCH X431 to BYD Sealion 7 OBD-II Port for Key Programming
• BYD Qin Plus DM-i Key Matching with LAUNCH X431 IMMO Elite | Step-by-Step Guide