The problem of the Xiaomi Redmi Note 9 smartphone screen continuing to burn during a phone call is familiar to many users. It is not just uncomfortable, but can lead to accidental cheek pressing, resetting a call or turning on the hands-free at the most inopportune moment. The proximity sensor responsible for locking the display can work incorrectly for various reasons, from banal contamination to software failures in the MIUI shell.
In most cases, you can fix things yourself without going to the service center, and often just wipe the top of the screen or calibrate it through the engineering menu, but if the software methods don't work, it might be physical damage or a poor protective film that override the sensor.
In this article, we will discuss all possible causes of malfunction and offer step-by-step solutions. You will learn how to diagnose the Redmi Note 9, use hidden system functions and when to think about replacing hardware components. 80% of the time the problem is solved by software calibration or cleaning the sensor area.
Principle of operation of the proximity sensor and causes of failures
To understand the problem, you need to understand how the screen shutdown works. At the top of the display, next to the speaker, there's a special infrared sensor that emits invisible light and reads its reflection. When you hold the phone to your ear, the beam bounces off the skin surface, and the system receives a signal that the device is near the face. MIUI algorithms instantly respond to this change, extinguishing the display to avoid false presses.
However, in the Redmi Note 9, as in many other Xiaomi smartphones, this sensor can behave unpredictably. Sometimes it "thinks" that the phone is still near the ear even when you removed it and the screen remains black. Other times, which is more common, it simply does not see the obstacle, and the display continues to glow. This can be due to pollution, software bugs or physical damage after a fall.
⚠️ Attention: Constantly burning screen during a conversation is not only annoying, but also significantly accelerates battery discharge, since the display is one of the most energy-intensive elements of the smartphone.
A common cause of failure is malfunctioning of the operating system after an update. A new security patch or Android version may conflict with sensor drivers. It is also worth considering the influence of third-party applications that can intercept control of the sensor or change the energy saving settings, preventing the correct operation of the infrared sensor.
Diagnostics and check of sensor serviceability
Before you start complex manipulations, you need to make sure that the sensor is physically healthy and capable of responding to objects. Xiaomi smartphones have built-in engineering mode, allowing you to test all hardware components without installing third-party software, this is the most reliable way of initial diagnosis.
To enter the test mode, open the Phone app and enter a special code. Type ##6484#. Immediately after entering the last digit, the CIT menu will open. In the test list, find a item called the Proximity sensor or Approximation Sensor. Click on it to start checking.
In the window that opens, you'll see a numerical value. Usually, when nothing covers the top of the screen, the value is 5.0. If you close the sensor area with your palm or finger, the value should change to 0.0. If the numbers change, then (the iron) is good, and the problem lies in the software part or calibration. If the value remains unchanged (for example, constantly 5.0), this can indicate a physical breakdown or severe contamination.
- 🔍 Make sure that the protective glass or film does not overlap the area of the sensor located next to the speaker.
- 🧹 Wipe the top of the screen with a soft cloth, removing fat and dust that can distort readings.
- 📱 Check if the film is incorrectly (shifted), which often happens after replacing the display in the service.
Programmatic calibration of the proximity sensor
If testing shows that the sensor is responsive, but the screen is not going out in real calls, you need to calibrate, which is a process where you train the system to correctly define the boundaries between "screen open" and "screen closed." In Redmi Note 9, this procedure is performed through the same CIT engineering menu.
When you're in the Proximity sensor, press Calibration. The system will ask you to remove your hand from the sensor and then close it. Follow the instructions on the screen. It's important to do things clearly and slowly. Once you've calibrated, the phone can automatically restart or suggest you save the results. Resetting the sensor often solves the problem of desynchronization.
What to do if the calibration does not pass?
If after a few attempts the system writes "Fail", try to completely turn off the smartphone, wait 10 seconds and turn on again. Sometimes it helps to temporarily turn off the battery (if you have experience disassembling), but for the Redmi Note 9, a normal reboot is enough. If the error persists, it's possible that the sensor is flooded or has a microcrack. There's also an alternative way of calibrating through a hidden engineering test menu, accessible through settings. Go to Settings. → The phone. → Version. MIUI and quickly press 10 times on the assembly number. In the menu that appears, select "Single-item Test" →"Proximity sensor. The same way of doing it is: close, open, confirm, system settings and avoiding accidental pressing. MIUI There are functions that can conflict with the operation of the sensor or, conversely, help it. First of all, check your settings to prevent random switching. This feature uses the accelerometer and proximity sensor data to lock the screen in your pocket, but sometimes it doesn't work correctly. Go to the Settings menu → Lock screen. Find the option "Mode in your pocket" (or "Preventing accidental taps"). Try to switch this switch: if it's on, turn it off, and vice versa. Reset the device and check the screen during the call. Sometimes, simply resetting this setting to a default value eliminates a logical error in the operation of the systems. In some versions MIUI for different regions (Global, China, EEA) The impact of protective accessories and cases One of the most common but frequent causes of the problem is improperly selected accessories. 3D-The proximity sensor in this model is very close to the edge of the speaker, and even a minimal patch of glass can block the IR beam. If you have recently changed the security glass, try to remove it carefully and check the phone without it. Glass with a black perimeter frame ("full glue" or frame) is especially often the culprit of the malfunction, as the black stripe can be wider than the design of the smartphone requires. Optical gap between glass and sensor is critical. Accessory type Probability of problem Solution Tempered glass with frame High Replace with glass without frame or cut out the hole Hydrogel film Low Check the quality of the sticker (bubbles) Thick silicone case Medium Remove the case during the call or replace with a thin magnetic holder (ring) Medium Do not glue the ring on the upper part of the body ⚠️ Warning: If you use a hydrogel film, make sure that there are no air bubbles underneath it in the sensor area, and the bubble acts as a lens and can distort the sensor readings. If none of the above methods worked, there may have been a deep software failure or application conflict in the system. Some memory cleaners, antiviruses or call management applications can intercept the sensor. Try to start your phone in Safe Mode. To do this, press the power-off button, and when the power-off icon appears on the screen, press and hold it for a few seconds until you have a suggestion to go to Safe Mode. Safe Mode is only running system applications. Call someone. If the screen goes out correctly in this mode, it means that one of the apps you installed is to blame. Start removing newly installed programs, especially those related to calls, recording conversations or optimization. 💡Before you completely reset, make sure to back up your contacts and photos to your Google or Mi Cloud account, as all data will be deleted.A cardinal but often effective solution is a complete factory reset.Go to Settings → The phone. → Resetting settings → Erase all data. This will bring the Redmi Note 9 software back to its original state by removing all configuration errors. If the problem persists, there's a 99% chance it's hardware. When you need to repair and replace parts, situations where software methods are powerless also happen. If the sensor does not respond to CIT-The menu (value does not change), the screen is broken at the top, or the phone fell into the water, you need to replace the part. In the Redmi Note 9, the proximity sensor is often integrated into the charging port plume (in some versions) or is part of the top plume going to the main board. Replacing this part requires the ability to disassemble the smartphone, you need to carefully disconnect the plumes, remove the battery and replace the sensor module. If you are not sure of your abilities, it is better to contact an authorized service center, so as not to damage other components. 💡If calibration and reset didn't work, and in the engineering menu, the sensor shows a static value, you need to replace the hardware component. Why does the screen go out only in messengers (Viber, WhatsApp), but it works in a regular call? API A standard call takes priority over a system, and messengers (VoIP) can work through other services. Try updating a particular application or clearing its cache in the application settings. Can an Android update break the sensor? Yes, sometimes new versions MIUI Android or Android contain bugs that incorrectly process data from sensors. In such cases, waiting for the next security patch or, conversely, rolling back on the previous version of the firmware (which is more complicated and requires unlocking the bootloader) helps. Does the ambient temperature affect the operation of the sensor? Extremely low or high temperatures can temporarily disrupt the operation of electronics, including infrared sensors. If you are in the cold or in the direct sun, try warming or cooling the phone to room temperature and check again.