Why the fingerprint scanner on Xiaomi Mi 9S stopped working – deal with the expert
You're used to unlocking the Xiaomi Mi 9S with a single touch, but suddenly the fingerprint scanner stopped responding? The situation is familiar to many owners of this smartphone - the problem can manifest itself after updating the firmware, and for no apparent reason. In 80% of cases, software failures are to blame, but sometimes it is hardware malfunctions of the module or the plume.
In this article, we will take a look at all possible causes, from the commonplace contamination of the sensor to damage to the controller chip, and you will receive step-by-step instructions for diagnosis and recovery, and when to contact the service center. 9S, where the scanner is integrated into the screen and sensitive to overheating of the Snapdragon 855 processor+.
Before you start repairing, check if the sensor responds to touch with a vibration or an audible signal, if so, a software problem, if not, probably hardware. We'll go over both scenarios next.
1. Software glitches: from updates to application conflicts
The most common reason for the disappearance of a fingerprint is a MIUI malfunction, especially after automatic updates, when new firmware versions conflict with old data from the biometric module, for example, after upgrading to MIUI 14, many Mi 9S users complained about missing saved fingerprints.
Other program triggers:
- 📱 Install custom firmware (such as LineageOS or Pixel Experience) without the right sensor drivers.
- 🔄 Conflict with applications requesting access to biometrics (banking programs, password managers).
- 🗑️ Cleaning the system cache through Settings → Warehouse → Cleaning with removal of critical module files.
- 🔋 Battery discharge up to 0% followed by improper session recovery.
The first thing you need to do is to restart your smartphone in safe mode.
- Press the power button before the off menu appears.
- Press and hold the “Switch Off” option (or “Reboot” in new versions of MIUI).
- Confirm the transition to safe mode.
If you're in safe mode, it's the third-party app's fault, and you can delete the newly installed programs one by one, starting with the ones that requested access to the biometrics.
Hardware malfunctions: from pollution to plume break
The Xiaomi Mi 9S uses an ultrasonic fingerprint scanner built into the screen, which is more reliable than optical counterparts, but is sensitive to physical damage.
| Type of malfunction | Signs. | Can I eliminate it on my own? |
|---|---|---|
| Sensor pollution (dust, fat, moisture) | The scanner does not respond or it will work again. | Yes. |
| Damage to the connection plume | There is no vibration/lighting when touching. | No (repair needed) |
| Cracks in the scanner area (even microscopic) | It only works from a certain angle. | No. |
| Overheating of the processor (Snapdragon 855+) | The scanner is turned off at high load | Partially (cooling) |
For diagnosis:
- Light a flashlight on the scanner area at an angle - visible scratches or stains indicate contamination.
- Try registering a new fingerprint: if the process is interrupted during the scanning stage, it is a hardware problem.
- Check the body temperature with the AIDA64 app. If the CPU is heated above 60°C, the scanner can shut down for protection.
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If the scanner stopped working after the fall of the phone, do not shake or knock on the body - this can permanently damage the plume.
3. Resetting biometric settings: step-by-step instructions
If the scanner is physically fit but the prints are not saved or recognized, biometric data resetting can help, a technique that works in 60% of software failures.
Instructions:
- Go to Settings → Passwords and Security → Fingerprints.
- Remove all the fingerprints (if they are displayed).
- Go back to the main settings menu and select Applications → Application Management.
- Find com.android.biometrics (or BiometricService) and open its settings.
- Click on “Clear Data” and “Clear Cache”.
- Reboot the phone.
After you restart, try adding the fingerprint again, and if the process is smooth and the scanner is still not working, move on to the next step.
Remove all fingerprints from the system
Clear the cache of the BiometricService application
Reboot the phone
Check the scanner in safe mode-->
4. Update firmware and rollback to stable version
Firmware errors are the second most common cause of scanner problems. For example, MIUI 12.5.3 for the Mi 9S had a bug that stopped the biometric module from initializing after sleep, so the solution is to upgrade to the latest stable version or roll back to the working version.
How to update the firmware correctly:
- 📲 Use the official Update app (not third-party utilities!).
- 🔋 The battery charge must be at least 50%.
- 📶 Connect to Wi-Fi – Downloading on the mobile network may be interrupted.
- 🔄 After the update, reset the biometric data (see previous section).
If the problem occurs after the update, try to roll back:
- Download stable firmware for Mi 9S (codename grus) from the Xiaomi Firmware website.
- Rename the file to update.zip and place it in the root of the phone’s memory.
- Go to Settings → About the phone → System update.
- Click on the three dots in the upper right corner and select "Select firmware file."
What to do if the update is suspended?
5. Diagnostics of hardware damage
If the software methods didn't work, you'll have to check the hardware, and let's start with the simplest one: cleaning the sensor.
- 🧴 Use isopropyl alcohol (70% or higher) and a lilaless napkin.
- 🚫 Do not use abrasive materials or liquids based on acetone.
- 🔍 Gently wipe the scanner area in circular motions, then let it dry for 5 minutes.
If the cleaning didn’t help, check:
- Connection plume: when it falls, it can move away from the connector on the motherboard.
- Microcracks on the screen: Even invisible damage to the eye disrupts the ultrasonic sensor.
- Scanner controller: if overheating or voltage surges, it can fail (a chip replacement is required).
For a deep diagnosis, use the engineering menu:
#4636## → Testing equipment → Fingerprint TestIf the test shows a Hardware not found or Communication error, the hardware malfunction is a problem.
6. When to contact the service: prices and guarantees
If the manipulations have failed, it is time to contact professionals.The cost of repairing the fingerprint scanner on the Xiaomi Mi 9S varies depending on the problem:
| Type of repair | Cost (₽) | Timeline | Guarantee |
|---|---|---|---|
| Sensor cleaning + plume soldering | 1 500 — 2 500 | 1 day | 3 months |
| Replacement of the ultrasound scanner | 3 000 — 5 000 | 2-3 days | 6 months |
| Controller repair (chip replacement) | 4 000 — 7 000 | 3-5 days | 1 year |
| Replacement of the display module (with scanner) | 8 000 — 12 000 | 5-7 days | 1 year |
When choosing a service, pay attention to:
- 🔧 Original parts (ask for a Goodix or Qualcomm scanner certificate) 3D Sonic).
- 📄 Guarantee of at least 6 months for repair work on biometric module.
- 📊 Reviews of a particular master (in forums) 4PDA or Mi Community).
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Before visiting the service, back up your data via Settings → Additional → Backup. When replacing the scanner, you may need to completely reset your phone.
7. Alternative methods of unlocking if the scanner is not working
While the scanner is being repaired, use alternative unlocking methods:
- 🔐 PIN-code or pattern lock: you can configure in Settings → Lock screen.
- 👤 Facial recognition: less secure but convenient. Included in Settings → Passwords and security → Facial recognition.
- 📱 Smart Lock: Automatically unlock in trusted locations (home, work) or when connected to a trusted device (e.g. Mi Band).
- 🔑 Temporary Password: Some banking applications (e.g. SberBank Online) allow you to generate a one-time login code.
If you forgot. PIN-If you have a code, and the scanner is not working, you have to do a hard reset:
- Turn off the phone.
- Press the Power button + Volume up until the Mi logo appears.
- Select Wipe Data → Wipe All Data from the Recovery Menu.
- Confirm the action and wait for the reboot.
⚠️ Warning: Hard reset removes all data from your phone, including photos, messages and apps. If you have backup enabled in Mi Cloud, restore the data after the reset.