Why the fingerprint sensor on Redmi 9 may fail
The fingerprint scanner on Xiaomi Redmi 9 is a convenient feature for quick unlocking, but sometimes it stops working for no apparent reason. Users face problems: the device does not recognize the fingerprint, the sensor does not respond to touch or is not at all in the settings, the causes can be hidden in software failures and physical damage.
In this article, we will look at all possible causes of malfunction, from the commonplace contamination of the sensor to serious hardware failures, learn how to diagnose the problem yourself, what settings to check first, and when to contact the service center, and pay special attention to the typical user errors that make the situation worse.
If your Redmi 9 has stopped recognizing fingerprints after a MIUI update or a fall, don’t rush to carry it for repair. 80% of the time, you can solve the problem yourself – just follow the instructions below.
1. Pollution of the sensor or protective glass
The most common cause is dirt, grease, or moisture on the scanner surface, and the fingerprint sensor on Redmi 9 is on the back, and it's in constant contact with your fingers, pockets, and surfaces, and over time, it builds up dirt that blocks reading.
How to check:
- 🔍 Inspect the sensor under bright light – visible scratches, stains or greasy plaque?
- 🧴 Wipe the surface with a soft lilaless cloth soaked in alcohol (at least 70%).
- 🚫 Do not use abrasive materials (glass wipes, paper) – they scratch the glass.
If the sensor is working after cleaning, but after a while the problem returned, the reason may be a worn protective glass. On Redmi 9, it often wears off after 1.5-2 years of active use. ~500–800 ₽).
⚠️ Warning: Don't blow on the sensor or heat it up with a hair dryer. This can damage the chips inside the module.
2. Mishapes in MIUI or firmware
Software errors are the second most common cause of a failed scanner, and once the MIUI is updated or reset, the sensor can:
- 🔄 Stop responding to touch.
- 🚫 Disappear from the Settings menu → Passwords and security.
- ⚠️ Error: "I failed to add a print".
How to fix it:
- Reboot your phone (hold Power + Volume up 10 seconds).
- Clear the system cache: Settings → Applications → Application management → Three points → Show system → Biometric service → Storage → Clear the cache.
- Reset the sensor settings: delete all saved prints and add them again.
If the problem has occurred after the MIUI update, try to roll back to the previous version via Settings → About Phone → System Update → Three points → Select an update pack. Download the old firmware from the official Xiaomi website (section Redmi 9, encoding lancelot).
How to find an old firmware for Redmi 9?
3. Conflict with shell or third-party applications
Some applications (especially launchers, antiviruses, or ad-blocking software) can block biometric sensors, such as Nova Launcher or 360 Security, which sometimes conflict with Xiaomi services.
How to identify the culprit:
- 🛡️ Start your phone in safe mode (hold power). → Click "Switch off" → If the sensor is running, the problem is with third-party software.
- 🔍 Check permissions for applications: Settings → Annexes → Permits → Body. → Biometric data.
- 🗑️ Remove newly installed programs (especially those that requested access to security settings).
If the conflict is caused MIUI-shell (for example, after installing a custom theme), reset the theme settings to standard: → Display. → Style of design → By default.
💡
Before removing apps, check reviews in Google Play – users often write about such bugs.
4. Physical damage: falls, moisture, wear and tear
The fingerprint sensor on Redmi 9 is connected to the motherboard with a thin plume.Even a minor impact or fall can disrupt contact.
- 💥 The sensor does not glow when touched (on Redmi 9 it is illuminated with white).
- 🔌 The phone doesn't respond to any prints, even after being reset.
- 💧 There were signs of corrosion (green plaque) around the sensor after moisture hit.
What to do:
- If the phone falls, don't take it apart. The sensor plume is fragile, it's easy to damage.
- If moisture is ingested, do not turn on the device for 24-48 hours and take it to the service for cleaning.
- If the sensor is physically damaged (cracks, dents), you will need to replace the module (cost) ~1 200–1 800 ₽).
⚠️ Warning: Do not try to "fix" the sensor with heat or pressure. This can lead to a short circuit of the board.
| Type of damage | Signs. | Decision | Cost of repair |
|---|---|---|---|
| The plume rupture | Sensor doesn't respond, but it glows. | Pillowing the plume | 800–1 500 ₽ |
| Corrosion after moisture | Green raid, phone bugging. | Cleaning with ultrasound + replacing the sensor | 1 500–2 500 ₽ |
| A crack in the sensor glass | Visible damage, false positives | Replacement of glass or module | 500–1 800 ₽ |
| Contact dump on the board | Sensor's working in a second. | Contact soldering | 1 000–2 000 ₽ |
5. Resetting and flashing
If the software methods didn't work, the last step before you went to the service is to completely reset the settings, which will delete all the data, but it will return the factory parameters of the MIUI, including the sensor.
How to reset:
Save important data to your PC or cloud |Remember the username/password from Mi-account | Charge your phone at least 50% | Turn off two-factor authentication in Mi-account-->
- Go to Settings → About Phone → Resetting → Erase all data.
- Enter the password from Mi-account (if you forgot, restore it via account.xiaomi.com).
- Confirm the reset. The phone will reboot and start setting up from scratch.
If the reset didn’t work, you’ll have to flash through Fastboot, which is a complicated procedure that requires PC and command knowledge, and see the steps in Xiaomi’s official documentation (Unlock & Flash).
💡
Setting reset deletes all data, including photos and messages. Always back up before the procedure!
6. When to contact the service center
If you’ve tried all the techniques, but the fingerprint sensor on Redmi 9 still doesn’t work, it’s time to contact the specialists.
- 🔧 The sensor is not detected in the diagnostic menu (#4636## → "Testing of equipment").
- 💻 The error appears on the screen: Hardware error: Fingerprint sensor".
- 🔄 The phone spontaneously reboots when you try to add a print.
Where to repair:
- 🏢 Xiaomi service centers – 6-12 months warranty, but more expensive (diagnostics) ~500 ₽).
- 🔧 Local workshops are cheaper, but check reviews and spare parts availability.
- 📦 Replace yourself – only if you have soldering experience (the sensor module for Redmi 9 is worth it). ~1 000 ₽ AliExpress).
Average cost of repairs in Russia (2026):
- Diagnosis - 300-500 ₽.
- Replacement of sensor – 1,200–1,800 ₽ (work).
- Repair of the plume - 800-1 500 ₽.
7. Alternative ways of unlocking
While the fingerprint sensor is not fixed, use alternative unlock methods:
- 🔐 PIN-A code or pattern lock is the most reliable option.
- 👤 Facial recognition (less secure but quick) is enabled in Settings → Passwords and security → Facial recognition.
- 📱 Smart Lock – Automatically unlock in trusted places (home, work). → Passwords and security → Smart Lock.
If you use Mi Band or other Xiaomi devices, you can set up unlocking through them:
- Connect the gadget to the phone via Mi Fit.
- Activate the option Unlock the phone in the bracelet settings.
⚠️ Attention: Don't turn it off PIN-The code is complete, even if the sensor is not working, and it will make your phone vulnerable to data theft.