The proximity sensor issues on Xiaomi smartphones, particularly the popular Redmi Note 9S, are one of the most common reasons to contact service centers and support forums. The situation when the screen goes out on its own or, conversely, does not turn off during a conversation, allowing the cheek to accidentally press the reset or volume button, is familiar to many owners. It is not just a small bug, but a serious inconvenience that can lead to unplanned costs for mobile communications or the loss of important contacts.
In most cases, the hardware is in good shape, and the problem is that the software fails or the light sensor is not calibrated correctly. Android on the MIUI shell sometimes misreads data from the top end of the case where the module is located. Fortunately, 90% of the time, you can fix the situation yourself without having to repair or re-flash the gadget. We'll look at all the effective diagnostic and adjustment methods.
Before embarking on radical measures such as factory resets, it is worth trying software correction methods. Often, just retrain your smartphone to determine the distance to an object. In this article, we will discuss in detail the step-by-step algorithm of actions that will help return the Xiaomi Redmi Note 9S to normal operation. Follow the instructions carefully to avoid errors.
Diagnostics and check of sensor performance
The first step is always to make an accurate diagnosis. Don't wonder if the sensor is working or not, use the built-in tools of the system to get objective data. On Xiaomi devices, there is a hidden engineering menu that is accessed through the standard dialing interface, and this is the most reliable way to know whether the hardware sees your finger or the security glass.
To enter the test mode, you need to dial a special combination of characters. Open the Phone app and enter the code ##6484##. Immediately after entering the last star or grille (depending on the firmware version), the CIT menu (Customer Integration Test) will open. Here is a complete list of all the components of the device. You need to find the item associated with the Proximity Sensor or Approximation Sensor.
Inside the test, you'll see a digital value. When you don't touch anything at the top of the screen, it should be close to 0 or 5.0 (depending on the software version). If you put your hand in the area of the speaker, the numbers should change. If you don't respond, it means the problem may be hardware or caused by severe pollution. It's also worth checking if the sensor is covered with a protective film or a case.
⚠️ Attention: If the test shows a constant "0" in the engineering menu, even when closed with your hand, the sensor plume may have moved away after falling.
After the initial test, you can switch to software calibration, which forces the system to remember current readings as "normal" and "proximity," and often resetting these readings solves the problem of false positives during calls.
Calibration through CIT Engineering Menu
The most effective way to set up the proximity sensor on the Xiaomi Redmi Note 9S is to use the same CIT engineering menu, but with a calibration function. This method allows you to overwrite the calibration data directly in the module memory.
Re-enter the menu with code ##6484## and select "Proximity Sensor" and the "Calibrate" or similar button will appear on the screen. Before starting the process, make sure that the front panel of the smartphone is completely clean.
The algorithm of actions during calibration is as follows:
- 📱 Click the “Calibration” button in the test menu.
- 👐 Remove your hand from the screen and wait for the “Pass” message or green indicator to appear.
- ✋ Close the sensor with your palm (without touching the screen) and wait for confirmation again.
- ✅ If the test is successful, the system will automatically save the new parameters.
It's important to understand that calibration is not a magic button, but a process of writing reference values. If the problem persists after the procedure, you may need to reset the data completely or check for conflicting applications. Sometimes the system can't calibrate the sensor correctly because of software errors in the current session.
☑️ Checklist before calibration
Reset sensor data through the developer menu
If standard calibration fails, you can try a deeper reset through the developer menu, which is especially relevant if the sensor is not working properly after the MIUI update, and we need to find a hidden option that compulsorily clears the sensor cache.
To start, activate the developer mode. Go to Settings → About Phone and quickly click 7 times on MIUI Version. Once you have become a developer, go back to the main settings menu. Go to the "Additional" section and select "Developers".
Inside the developer menu, scroll down to the section that's associated with input or touch panels, and we're interested in the option of Disable proximity sensor. Some versions of the firmware may call it something else. Activating this slider completely ignores the sensor, which is a temporary solution, but helps diagnose the problem.
But we're interested in another aspect, and this is also a menu that often has the option of resetting sensor calibration, and if you find Sensor calibration or Reset sensors, press it, and then the phone can reboot, and this action brings all sensors (accelerometer, gyroscope, approximation) back to factory values.
⚠️ Warning: Do not change other settings in the developer menu unless you are sure of their purpose. DPI Animations or animations can make the interface uncomfortable to use.
It’s worth noting that on newer versions of Android, some items can be hidden or renamed.If you don’t find the right option, try using third-party utilities that have access to these features through special permissions.
Use of third-party applications for calibration
When Xiaomi’s built-in tools fail, Google Play Store apps come to the rescue, using the same system calls but providing a more user-friendly interface and additional logging features. One of the most popular and proven tools is the Proximity Sensor Reset/Fix app.
The principle of such programs is to force the sensor service to restart, and the application requests permission to change the system settings and performs a reset, which often helps if the system has accumulated software "junk" that interferes with the correct operation of the equipment.
The process of using third-party software is usually simple:
- 📥 Download a high-rated app (such as from Kieron developer or analogues).
- 🔓 Provide the necessary permissions at the first launch.
- 🔄 Press the big button “Calibrate” or “Reset».
- 📵 Wait for the process to complete and restart the device.
If the sensor is flooded with water or broken, no program can make it work, but as a software crutch for fixing MIUI bugs, they work perfectly.
Why are third-party apps working?
Influence of protective glasses and covers
One of the most common but common reasons for sensor failure on the Redmi Note 9S is poor-quality protective glass. The design of the smartphone is such that the sensor is located very close to the edge of the speaker. If the glass is black or just too thick, it blocks the infrared beam.
So the phone thinks it's in your pocket or your ear, and it turns off the screen immediately after dialing, and it's easy to check that, take off the case and wipe the top of the screen, and if the problem's gone, it's the accessories, and in some cases, sticking a special transparent sticker to the sensor area helps, but it's a temporary solution.
Also, consider the presence of magnetic latches on bookcases. The magnetic field can (interfer with) the magnetometer and other sensors, causing the system to behave chaoticly. If you use such a case, try removing it and checking the phone's performance in its naked form.
The table below will help you quickly determine the likely cause of the problem depending on the symptoms:
| Symptoms. | Probable cause | Method of decision |
|---|---|---|
| The screen goes out immediately after the set | Dirt or thick glass | Cleaning or replacing glass |
| The screen doesn't go out when you ring. | Calibration failure | CIT's Engineering Menu |
| Accidental cheekstrokes | Wrong trigger threshold | Resetting through the application |
| The sensor doesn't respond at all. | Hardware cliff | Service centre |
| This table is of a reference nature |
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Try temporarily disabling Safe Mode or Pocket Mode in the lock settings to check if the system is blocking the sensor programmatically.
Radical measures: resetting and reflashing
If none of the above methods work, the last software option is a complete data reset (Hard Reset), which will delete all user data, so be sure to back up important information before starting the procedure.
To perform the reset, go to Settings → About Phone → Settings Reset → Erase all the data. It takes a few minutes. After turning on the phone, don't rush to install all the applications at once. First check the sensor on the clean system. If it works, there was a problem in one of the installed applications.
In extreme cases, when even the reset doesn't work, users resort to flashing the device, whether it's switching from the global MIUI to the Chinese version or vice versa, or installing custom firmware, but it's a complicated procedure that requires unlocking the bootloader, which can lead to a loss of warranty.
⚠️ Warning: Flashing your phone without proper qualifications can turn your device into a brick. If you are not sure of your abilities, you better consult a specialist.
It is also worth mentioning that some versions of MIUI firmware have known proximity sensor bugs that only patch security updates.
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95 percent of sensor problems are solved by cleaning glass and calibrating through an engineering menu, and hardware breakdowns are much less common.