Mechanic Wiki: How to Resolve BYD IMMO Security Code Errors with LAUNCH X431

Fix BYD IMMO security code errors during key programming with LAUNCH X431. Step-by-step guide covering software updates, vehicle selection, manual code entry, and advanced troubleshooting.

Published: May 26, 2026

Quick Answer

If your LAUNCH X431 shows a BYD IMMO security code error during key programming, the culprit is usually outdated scanner firmware, incorrect vehicle model selection, or a locked ECU after multiple failed attempts. To fix it: update your X431 to the latest BYD software, select the exact BYD model and year (not just “BYD”), use the dedicated IMMO function, and if the code still fails, try the online security code reset or contact LAUNCH support for a manual unlock.

Understanding BYD IMMO Security Codes and LAUNCH X431

What is BYD IMMO?

BYD (Build Your Dreams) vehicles use an immobilizer system (IMMO) that prevents the engine from starting without a correctly programmed key. The system relies on an encrypted transponder chip in the key fob and a security code stored in the engine control unit (ECU). When you attempt to program a new key with a diagnostic tool like the LAUNCH X431, the scanner must either read that security code from the ECU or accept a manually entered code. If the code is wrong, the ECU rejects the key and throws a “Security Code Error.”

Common reasons this error pops up:

The security code you have is in the wrong format (e.g., 4-digit vs. 6-digit).
The ECU has locked itself after three or more failed attempts.
The vehicle has aftermarket parts (e.g., a replaced ECU) that don’t match the original PIN.
The scanner is using an outdated security algorithm for that specific BYD model.

How LAUNCH X431 Handles BYD Key Programming

The LAUNCH X431 series (PAD, V, Pro, etc.) is one of the most popular multi-brand diagnostic tools because of its extensive BYD coverage and cloud-based IMMO functions. When you navigate to the IMMO menu, the X431 can:

Read the security code directly from the ECU (online or offline).
Accept a manual security code if you already have one.
Calculate the code from the VIN using an online server (subscription-dependent).
Perform key learning and erase old keys.

The key is to use the dedicated “IMMO” menu rather than a generic “Key Programming” function under a different system. BYD’s immobilizer is tightly integrated with the BCM (Body Control Module) and sometimes the engine ECU, so the X431 needs to know exactly which protocol to use.

Typical Error Codes You Might Encounter

When things go wrong, the LAUNCH X431 will display one of these messages:

Error Message	What It Usually Means
“Security Code Error”	The entered code does not match the ECU’s stored code.
“Invalid Key”	The transponder chip is not recognized – either wrong type or faulty key.
“Communication Failure with ECU”	The scanner cannot talk to the IMMO module – check connections, voltage, or protocol.
“Code Not Accepted”	The ECU rejected the code – often due to lockout or wrong algorithm.

Prerequisites Before Programming

Before you even connect the LAUNCH X431, take these steps to avoid wasting time:

Tool Requirements: Make sure your X431 model has the latest BYD package installed. Most X431 units support online updates – check under Menu > Settings > System Info. If the BYD software is older than six months, update it.
Vehicle Preparation: The battery voltage must be above 12.5V. Low voltage is a common cause of “Communication Failure” errors. Keep the ignition on (engine off) and close all doors to avoid CAN bus interference.
Key Considerations: Verify the transponder type in your new key. Common types for BYD include 4D70, Hitag2, and 46 chip. Using a key with the wrong transponder will always fail.
Backup Security Code: If you can get the original security code from the dealer (or a reliable third-party service), write it down. Even if the X431 can read it automatically, having a known good code is your safety net.

I once worked on a BYD F3 that kept showing “Security Code Error” because the customer had bought a cheap aftermarket key with a 4C chip instead of the required 46 chip. Double-checking the key type saved hours of troubleshooting.

Step-by-Step Troubleshooting for Security Code Errors

Step 1: Confirm Scanner Software and Database Version

Open your LAUNCH X431 and go to Menu > Settings > System Info. Look for “BYD” under “Installed Software” and note the version number. Then connect to Wi-Fi and open the Update Center. Download any available BYD software updates – these often contain new algorithms for newer BYD models.

Common mistake: Many technicians update the LAUNCH’s Android OS but forget to update the diagnostic application itself. Always update the “X431 Diag” app and the specific BYD package.

Step 2: Correct Vehicle Selection

Do not select the generic “BYD” brand and hope for the best. You need the exact model and year – for example, “BYD F3 (2009-2015)” or “BYD Tang (2020-2023).” Some models have multiple ECU variants (e.g., Bosch vs. Continental). The LAUNCH X431 usually prompts you to choose based on the VIN if you use the “VIN Scan” option. If not, match the VIN manually:

Locate the VIN on the dash or door sticker.
Use the X431’s “VIN” entry field in the vehicle selection screen. It will automatically select the correct model if it’s supported.

Pro tip: If the scanner offers two similar models (e.g., BYD F3 with engine A vs. engine B), try the one that matches your vehicle’s production year first. If that fails, try the other – sometimes the database has a typo.

Step 3: Enter the IMMO Function Properly

Navigate as follows:

IMMO (main menu)
BYD (or sometimes under “China” brands)
Key Programming
Read Security Code

If “Read Security Code” works, great – the scanner extracts the code and displays it. Write it down before proceeding. If it fails (common on locked ECUs), you’ll see “Security Code Error” immediately. In that case, try “Enter Security Code Manually” if you have the PIN.

If the scanner asks for the original key count or number of keys to program, answer accurately. Some BYD models require you to enter the total number of keys you want to have working (including the old ones).

Step 4: Manual Security Code Entry – What to Do When It Fails

Format: Most BYD security codes are 4 digits, but some newer models (like the Han or Tang) use 6 digits. Enter the code exactly as provided – no leading zeros, no spaces.

Lockout: If you’ve already failed 3–5 attempts (the count varies by model), the ECU will lock itself for 15–60 minutes. The LAUNCH X431 usually shows a timer. Do not keep trying – wait it out or disconnect the battery for 30 minutes to reset the lockout counter (though this doesn’t always work).

Security Code Reset: Some X431 versions have a “Security Code Reset” function under the IMMO menu. This function attempts to unlock the ECU by sending a special command – it often requires an online authorization. If available, follow the on-screen instructions; it may ask for your LAUNCH account credentials.

Step 5: Programming the New Key

Once the security code is accepted, the X431 will guide you through “Start Learning” or “Program Key.” The usual process:

Place the new key in the ignition (turn to ON position, not start) or hold it near the key reader coil (for push-to-start models, usually near the steering column or start button).
Follow the on-screen countdown – typically 30 seconds.
The scanner will beep or show “Key Learned” when successful.

Critical: Almost all BYD models erase all existing keys when you program a new one. That means you must have all your keys present during the session. After programming the new key, immediately re-add the old keys one by one. If you forget, the old keys will no longer start the car.

Step 6: Clear Error Codes and Finalize

After programming, use the LAUNCH X431 to clear any fault codes from the IMMO ECU (under “Clear Codes” in the IMMO menu). Then test each key:

Start the engine.
Check remote lock/unlock.
Verify immobilizer warning light goes off.

If a key fails to start the car, repeat the learning procedure for that key.

Advanced Troubleshooting When Standard Steps Fail

Causes of Persistent Security Code Errors

Even after following all steps, you might still hit a wall. Here’s why:

ECU Locked Permanently: Some BYD ECUs require a dealer-level reset. The LAUNCH X431 can sometimes do this via the Online IMMO Support feature, but not all models are supported.
Wrong Security Algorithm: BYD uses different encryption algorithms depending on the ECU supplier (PRD, Bosch, Continental, etc.). If the X431 is using the wrong algorithm, the code will be rejected even if it’s correct. Try selecting a different “IMMO System” option within the same model – some X431 firmware versions list multiple entries for the same car (e.g., “BYD F3 IMMO 1” and “BYD F3 IMMO 2”).
Firmware Corruption: In rare cases, the ECU itself may have corrupted firmware. The X431 has an “ECU Update” function, but DO NOT use it unless you have a backup or a known working file. I’ve seen technicians brick an ECU this way.

Using LAUNCH X431 Online IMMO Support

If standard steps fail, use the Online IMMO Support feature:

Connect your X431 to the internet.
Go to IMMO > Remote Unlock or Online Support.
The tool will generate a diagnostic log and VIN report.
Contact LAUNCH technical support via the app or phone and provide the log.
They will send a temporary security code or a special unlock file that you load into the X431.

This service usually requires an active subscription (X431’s “Online IMMO” package). It’s very effective for stubborn locked ECUs.

Alternative Methods for Stubborn Errors

Switch to a different X431 model: If your old X431 Pro can’t handle it, try an X431 PAD V or X431 V. Sometimes the newer hardware has better protocol support.
Use a dedicated BYD key programmer: Tools like the Autel IM608 or Xtool X100 PAD have dedicated BYD modules that may bypass obstacles.
Check OBD wiring: A broken or corroded pin can cause intermittent communication. Verify pins 4 (chassis ground), 5 (signal ground), and 16 (battery power) are intact.

Tips for LAUNCH X431 BYD IMMO Success

Always run a full system scan before entering the IMMO menu. This ensures all modules are communicating and gives you a baseline of fault codes.
Keep the tool connected to the internet – the X431 often queries an online database for updated security algorithms.
For keyless (push-to-start) vehicles, locate the key reader coil. It’s usually a small plastic ring around the start button or under the steering column shroud. Hold the key exactly there during programming.
Document original key count: Before programming, note how many working keys the customer has. After programming, verify you didn’t lose any.

Frequently Asked Questions (FAQ)

Q: Why does my LAUNCH X431 keep saying “Security Code Error” even though I have the correct code?

The most common reasons are: (1) you selected the wrong vehicle variant – try a different model year or engine option; (2) the ECU has locked after too many failed attempts – wait 30 minutes; (3) the code you have is a dealer PIN that needs conversion – some X431 versions have an “IMMO Password” sub-function that converts dealer codes to ECU codes.

Q: Can I program a BYD key without any security code?

No, the BYD immobilizer always requires a security code. However, some LAUNCH X431 software can automatically calculate the code from the VIN if you use the “Auto Code” or “Compute PIN” feature under the IMMO menu. This works for many popular models like the BYD F3 and S6.

Q: How many key attempts do I have before the ECU locks?

Typically 3 to 5 attempts. After that, the ECU will lock for 15 to 60 minutes. The LAUNCH X431 usually displays a countdown timer. Do not attempt to bypass this – it’s a security feature.

Q: Do I need to bring all existing keys when programming a new one?

Yes. Most BYD models erase all stored keys when a new key learning process starts. You must have all existing keys available to re-add them during the same session. If you don’t, the old keys will stop working.

Q: My X431 cannot detect the BYD IMMO module. What should I do?

First, verify the vehicle is supported on LAUNCH’s official website. Then check the OBD connector – ensure it clicks firmly into place. Test the OBD port fuse (usually in the cabin fuse box). Try switching the X431’s protocol setting between CAN and K-Line (some old BYD models use K-Line). Finally, update the X431 software – compatibility issues are often fixed in updates.

Q: Is it possible to bypass the IMMO system entirely?

Technically yes, using aftermarket ECUs or bypass modules, but it is illegal in most countries and highly unsafe. Bypassing the immobilizer removes a critical anti-theft protection. I do not recommend it for any road-going vehicle.

Q: What is the difference between “Read Security Code” and “Enter Security Code”?

“Read Security Code” attempts to extract the code directly from the ECU. This is the best option because it eliminates human error. “Enter Security Code” requires you to manually type a code you obtained elsewhere. If the read function fails (usually due to a locked ECU), you’ll have to use the manual entry – but only if you have a valid code.

Q: My LAUNCH X431 shows “Online Authorization Failed” during IMMO. What now?

This means your X431 subscription has expired or the internet connection dropped. Check your subscription status in the app (Menu > Account). If active, try switching to a different Wi-Fi network or using a mobile hotspot. If it still fails, contact LAUNCH support – they can issue a manual authorization file that you can load via USB.

Final Thoughts

BYD IMMO security code errors can be frustrating, but they’re almost always solvable with a systematic approach. Keep your LAUNCH X431 updated, double-check your vehicle selection, and always have a backup security code if possible. For the toughest cases, LAUNCH’s online IMMO support team is quite responsive. Document every step – that log could save you hours the next time you encounter the same model.

About the Author: Erwin Salarda is an Automotive Service Equipment Technician based in the Philippines, specializing in computerized automotive diagnostic equipment such as OBD scanners and wheel alignment systems. Since 2012, he has been actively providing technical support, equipment installation, troubleshooting, after-sales service, and hands-on training for automotive service equipment used by workshops and automotive professionals.

He has received specialized training from international suppliers and manufacturers, including Launch X431 in Shenzhen, China, Lawrence Engineering Company in Guangzhou, China, and 3Excel Wheel Alignment Company in Shenzhen, China. Through these trainings, he developed advanced expertise in automotive diagnostics, calibration, wheel alignment systems, and computerized automotive service technologies.

Erwin Salarda provides professional after-sales support and technical training for automotive diagnostic and wheel alignment equipment, helping clients maximize the performance and proper use of their tools and systems. His experience covers equipment setup, software updates, calibration procedures, troubleshooting, and operational guidance for automotive workshops and service centers.

With more than a decade of experience in the automotive equipment industry, Erwin Salarda continues to support automotive businesses by delivering reliable technical expertise and practical training solutions.

For inquiries and equipment purchases, please visit https://carlifterph.com/

For more on key programming basics with LAUNCH tools, check out our guide on [link to related guide on LAUNCH X431 universal key programming steps].
To learn about immobilizer system types across different Chinese brands, see our article [link to related article on Chinese car IMMO systems].