The situation when suddenly goes out during a conversation on Xiaomi Redmi 9, familiar to many users and often causes irritation or panic. In most cases, this is a standard security behavior designed to block accidental clicks of the cheek, but sometimes the functionality stops working correctly. If the display does not light up after the distance of the phone from the ear or, conversely, fade in the hands, the problem lies in the proximity sensor or software conflicts of the MIUI shell.
This failure cannot be ignored, as it can lead to missed calls, call resets or the inability to use speakerphones. In this article, we will discuss in detail the physical and software causes of the malfunction, as well as provide step-by-step instructions for restoring the normal operation of the smartphone.
The principle of operation of the proximity sensor and its role in the system
The main culprit behind the screen going out is the infrared proximity sensor at the top of the body, which is designed to measure the distance to the object: when you hold the phone to your ear, the sensor detects the obstacle and signals the system to turn off the display. On the Redmi 9, this sensor is often embedded directly in the screen or under the protective glass, making it sensitive to contamination and external influences.
So technically, the process is this: the emitter emits invisible light that bounces off the object and hits the receiver. If the reflection is strong, the system thinks the phone is in the ear, and activates the energy saving mode, quenching the matrix. The calibration failure leads to false positives, where the screen responds even when there is no real obstacle, and understanding this mechanism is important for choosing a solution method.
Technical nuances of the sensor
It is worth noting that MIUI software takes precedence over hardware signals, which means that even a good sensor can be ignored by the system if a conflicting application is running in the background or a cache of errors is accumulated, so software factors must be excluded before disassembling the device.
The influence of protective glasses, films and covers on the operation of the sensor
The most common reason why the screen goes out is because of the wrong protective film or glass. Many accessories, especially those with a black edge or a full top stick, block the area of the sensor, which results in the sensor constantly “seeing” the obstacle and keeping the display off even when the phone is in your hand.
And it's also affected by pollution: greasy spots, dust, or water droplets in the area above the speaker can distort the readings. If you recently replaced the protective coating and the problem came right after that, it's almost certainly the quality of the materials that plays a key role: cheap glass can have insufficient transparency for infrared rays.
- 📱 Check if the protective glass covers the area above the speaker.
- 🧼 Carefully wipe the top of the screen with a degreaser or an alcohol wipe.
- 🛡️ Remove the protective film to test the hypothesis about its effect on the sensor.
- 📵 Make sure that the cover does not have protruding elements in the upper end area.
💡
Try to temporarily remove the case and wipe the screen: if the problem disappeared, then it was in the accessories, not in the breakdown of the smartphone.
In some cases, it helps to glue the glass using a thinner analogue that does not have a black frame.
Software calibration of the sensor through the engineering menu
If physical obstacles are eliminated, you need to perform software calibration, there is a hidden engineering menu in the MIUI shell that allows you to test and customize components, and a special code is used to enter it, which allows you to access diagnostic tools.
Open the Phone app and dial ##6484##. In the menu that opens, select Proximity sensor. Here you will see the current value: if it changes when you bring your hand to the screen (e.g., from 5.0 to 0.0), then the sensor is physically healthy. To reset the settings, click Calibration.
☑️ Algorithm of sensor calibration
After calibration, the system overwrites the trigger thresholds, which often helps if the screen goes out spontaneously, but if the sensor shows a constant value of "0" or "5" in the engineering menu, regardless of the position of the hands, this may indicate a hardware plume break or a sensor failure.
System settings and software updates
Often the problem lies in the bugs of the operating system itself. Xiaomi developers regularly release updates that fix driver errors. Go to Settings → About Phone → MIUI version and check for updates. Sometimes even re-installing the current firmware version through the restore menu helps.
Also worth checking is the lock and call settings. Some versions of the software have a random tap lock option that may conflict with the sensor. → Lock screen can solve the problem, although it will reduce the protection in the pocket.
| Action. | The way is on the menu | Efficiency |
|---|---|---|
| Clearing the cache | Settings → Storage → Cleaning | Medium |
| Resetting settings | Settings → Advanced → Reset | Tall. |
| Repeal of updates | Settings → The phone. → Three points. | Medium |
| Safe regime | Clip the switch off button | Diagnostics |
💡
Clean firmware installation with the removal of all data is a radical, but the most effective way to eliminate software conflicts.
Don’t forget that third-party calling apps (like Truecaller or Viber) may have their own screen management settings. Check the permissions of these apps in Settings → Apps → Permissions and make sure they have access to sensors.
Hardware malfunctions and problems with the plume
When software methods fail and the screen continues to go out, it can be a physical breakdown. In Redmi 9, the proximity sensor plume is often integrated into the plume of the display or lower board. Falls, bumps or moisture could damage the contacts. Visually, this is difficult to determine, it requires disassembly of the device.
⚠️ Warning: Self-disassembly of the smartphone voids the warranty. If the device is warranty service, immediately contact an authorized service center.
A common problem is that the plume connector is moving away from the motherboard. Careful reseating often returns performance. It's also worth looking at the sensor itself: if there are cracks or traces of oxidation on its surface, a replacement component will be required. In budget models, replacing the sensor separately may not be economically feasible, and the masters suggest replacing the entire display plume.
Another nuance is that the processor is overheated, and if you talk long or use navigation, the smartphone can get hot, causing temporary sensor failures, and if the screen goes out only after the screen is overheated. 15-20 minutes of talk, possibly a problem in the thermal interface or cooling system.
Third-party applications and software conflicts
It's not just system settings that affect display behavior, but applications that control battery brightness, battery frugality, or access calls can intercept sensor control, such as various "optimizers" or design themes that change system files.
To check, run your smartphone in Safe Mode, press the off button, and then hold your finger on the "Stop" item on the screen for a long time until you suggest that you go to Safe Mode, and if the screen is behaving correctly in this mode, then one of the apps you installed is to blame.
Remove newly installed programs one by one, check the results. Pay special attention to applications related to calls, contacts and interface management. Sometimes even memory cleaners can cause such failures due to aggressive optimization of processes.