When a smartphone suddenly stops recognizing its owner, it's a natural irritation: You put your finger on the fingerprint scanner, but the device either ignores the touch or gives an error. This problem affects both the budget models of Redmi and the flagship Xiaomi with subscreen sensors. Often the reason is not a failure, but a software failure or contamination.
Owners of MIUI-based devices and the new HyperOS experience this regularly after system updates, and the sensor may not work properly due to a protective film that disrupts sensitivity, or because of a downed screen calibration. Before carrying the phone into service, it is worth eliminating simple software errors.
In this article, we'll look at all the possible causes, from the elemental dirt under your finger to the complex hardware malfunctions of the plume, how to do deep cleaning of the sensor, perform engineering calibration and when to sound the alarm, and in 80% of cases, the problem can be solved by software methods without replacing parts.
The main reasons for failure of biometric authorization
The first thing to understand is that a fingerprint scanner is a complex optical or capacitive mechanism. If the fingerprint sensor stopped working, the system could simply "forget" the reference pattern or cannot read the current one due to interference. Android's built-in protection often blocks biometrics after rebooting or security updates.
A common cause is physical exposure to the screen, shocks, falls or extreme temperature changes can cause layers of the display to be layered, and in models with a subscreen scanner, this is critical, because the sensor reads the pattern through the glass. OLED-Matrix damaged in scanning area, recognition will become impossible.
It is also worth considering the impact of third-party software: Aggressive “memory cleaners” or power saving programs can force the system processes responsible for security to stop, as a result, the biometric service simply does not start when blocked.
- 📱 Pollution of the screen surface or the finger itself (water, fat, cream).
- 🛡️ Use of thick or poor quality protective glasses that block the signal.
- ⚙️ Failure of the system module com.android.keyguard after the update.
- 🔋 Aggressive energy saving, disabling the scanner's background services.
Software solutions and settings MIUI
Start with the software part. Often, just overloading the device is enough to reset temporary errors in the Touch ID module. However, if a simple reboot did not help, a deeper intervention in settings will be required.
Try to remove old prints and write them back. When you re-write, try to touch the sensor with different parts of your finger, changing the angle of inclination. The system will create a more complete digital profile, which will increase the likelihood of successful unlocking. Don't ignore the system's requests to add additional touch angles.
In some cases, it helps to turn off the “Increased Sensitivity” function in the screen menu if it is active, or, conversely, turn it on when using films. Go to Settings → Screen → Fingerprint mode (the path may vary depending on the version of MIUI). Experiment with these parameters, checking the result after each change.
☑️ Diagnostics PO
Note that there are updates to the system. Xiaomi often releases patches that fix biometrics bugs. If you have a beta version of the firmware installed, consider rolling back to a stable version, as test builds are more likely to have bugs.
Impact of protective glasses and screen calibration
One of the most common reasons why a fingerprint scanner doesn't work is because of the protective glass; underscreen sensors (especially optical sensors) are extremely sensitive to the thickness and quality of the material; cheap glass can have an air layer or insufficient transparency for infrared radiation.
If you've recently put on a new glass and the problem comes right after that, it's the problem. Try temporarily removing the protection and checking the sensor. If without the glass everything works perfectly, you'll need a glass labeled "Compatible with fingerprint sensor" or sensitivity adjustment.
⚠️ Note: After replacing the display or protective glass on models with a subscreen scanner, professional calibration through the engineering menu is often required. 50-70%.
To improve the grip of the finger on the glass, the screen settings sometimes have a calibration option, and although it's hidden in the stock firmware, there are special codes for entering the engineering menu, where you can run the Fingerprint Sensor Test, which will allow you to see if the system can see the finger at the hardware level.
Engineering code for verification
Hardware malfunctions and problems with the plume
If software methods are powerless, there's a high probability of physical failure. In smartphones with scanners in the switch (side) the problem is often oxidation of contacts or a plume break, and moisture trapped inside the case quickly disables these thin conductors.
In models with a subscreen scanner, the situation is more complicated: the sensor itself is soldered under the display or glued to the inside of it, if you hit it hard, the connector of the plume going to the motherboard could move away, in which case the phone may not see the fingerprint at all in the system.
It's also not possible to rule out the sensor module itself, which is less common, but it's possible when voltage surges or production fails, and if the device manager or diagnostics app (like Device Info HW) displays the scanner as "Not Found" or "Error," it's hardware.
| Type of scanner | Frequent cause of breakdown | Difficulty of repair | Probability of success |
|---|---|---|---|
| Sideways (in the button) | Oxidation of contacts, break of the plume | Low. | Tall. |
| Rear (separate module) | Mechanical damage, peeling off | Low. | Tall. |
| Subscreen (Optical) | Display damage, calibration failure | Medium | Medium |
| Underscreen (Ultrasonic) | Detachment of glue, damage to the controller | Tall. | Low. |
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If the scanner stopped working after water hits, drying rice will not help - urgent opening and cleaning of contacts with ultrasound in the service is necessary.
Specificity of the work of subscreen scanners
The technology of subscreen scanning requires the perfect fit of the display layers. Over time, the glue that captures the screen can dry out, forming micro-gaps. These gaps distort the light signal, and the optical sensor can not build a clear picture of the topography of the finger.
Another nuance is the brightness of the screen. Underscreen scanners often only work at a certain level of backlight. If you have Read or Vision Protection mode on, which makes the screen yellow or dim, this can interfere with the sensor. Try to maximize the brightness when you unlock.
Xiaomi owners with 120Hz refresh rate sometimes note crashes. High screen sensor survey frequency can conflict with print poll frequency. Try temporarily reducing refresh rate to 60Hz in screen settings and check if the problem disappears.
- 💡 Make sure the screen brightness is not minimal when unlocking.
- 🎨 Turn off dark themes and night mode for the test.
- 🔄 Reduce the screen refresh rate to 60Hz for stability check.
- 🧼 Wash the screen with microfiber before using the scanner.
When a visit to the service center is required
There are situations where self-repair is useless and even dangerous. If your Xiaomi smartphone fell from a height, the screen is broken or the body shows signs of a strong impact, the problem is almost certainly hardware.
Also, a visit to the master is mandatory if the scanner does not work after getting liquid, even if the phone continues to charge. Corrosion of the contacts of the scanner develops gradually: today it works once, and after a week the phone will cease to turn on completely due to a short circuit.
⚠️ Warning: If the phone is warranty, do not open it or try to flash unofficial firmware. Any interference with the software or violation of seals will void the manufacturer's warranty obligations.
In the service, specialists will diagnose plumes and, if necessary, replace the scanner module or display assembled. For underscreen scanners, screen repainting is often required, which is almost impossible to do at home.
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Before you go to the service, make sure to make a full backup of data to the cloud or PC. When you replace the display or board, data can be lost.
Prevention and proper operation
To ensure that biometric protection works long and reliably, follow simple rules of operation. Regularly wipe the screen and finger from fat and moisture. Do not overheat the device, as high temperatures negatively affect the adhesive layer under the display.
Use only high-quality security glass designed for your model. Cheap analogs can not only degrade the image quality, but also disrupt the sensor. When buying, check compatibility with the fingerprint scanner.
Don't store more than 5 fingerprints on your phone. The more profiles you have in your memory, the more CPU load you have compared, and the more likely you are to make a mistake. Leave only your thumbs and index fingers on both hands, which is enough for comfortable use.