The situation of the screen going off while talking on the Xiaomi Redmi 9C is familiar to many budget smartphone users: you hold the phone to your ear, the display turns off as it should, but when you remove the device, the screen stays black. It causes panic: you can't see who is calling, you can't complete a call or switch to speakerphone. The problem is very uncomfortable, turning a normal conversation into a fight with a gadget.
The most common culprit for this behavior is not hardware failure, but software failure or sensor contamination. The Redmi 9C uses an infrared proximity sensor that is built into the top of the display. If the system is reading data wrongly or if there is film on the glass, the screen will go out just in case, blocking control. It is important to understand the reasons to return the phone to normal functionality.
In this guide, we will discuss all possible methods of solving the problem in detail, you will learn how to calibrate sensors, clear the cache of system processes and check whether the MIUI shell malfunctions. We will not use complex debugging tools, all actions can be performed using standard smartphone tools.
Why the screen goes off on Xiaomi Redmi 9C: the main reasons
Before we go to radical measures, we need to understand the physical nature of the process. The screen goes out because of the proximity sensor. It's a tiny module that emits infrared light. When you bring the phone to your head, the light bounces off the surface and returns to the receiver, telling the system to lock the display. If this mechanism is not working correctly, the screen can go out spontaneously or not turn on again.
One of the common reasons Redmi 9C models use is the use of protective glass or low-quality film. Some accessories overlap the sensor area or create glare that confuses the sensor. Even a microscopic crack in the top speaker area can distort the readings, making the phone think it is near your ear.
Software failures are also important, because after you upgrade your Android operating system or your MIUI shell, your calibration settings can get lost, and even the clean screen will not respond correctly, and sometimes the problem lies in the background applications that intercept sensor control or create conflicts in the system.
Basic inspection and cleaning of the sensor area
The simplest and most often ignored step is physical cleaning. Dust, skin fat and dirt accumulate at the top of the smartphone, where the sensor is located. First, wipe the screen with a soft microfiber cloth, paying special attention to the area above the speaker. Don't use aggressive chemistry, just a slightly wet wipe.
If your Xiaomi Redmi 9C has a protective glass, carefully examine its edges, it may have peeled off or shifted by blocking part of the sensor, try temporarily removing the accessory and checking the phone without it, often it is the thickness or quality of the adhesive layer of the film that causes the IR emitter to malfunction.
Check if there's any mechanical damage to the top of the body, and even if the glass is intact, the impact could have displaced the sensor plume inside the body, and in those cases, software techniques may not work, and you'll need to visit the service center, but if there's no external damage, we'll move on to software setting.
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Use a cotton swab lightly soaked in alcohol to gently wipe the narrow strip over the speaker, often accumulating invisible dust blocking the sensor.
Instructions: Calibration of the proximity sensor through the engineering menu
The most effective way to get the screen to stop going out at the wrong time is to calibrate. Xiaomi smartphones have a hidden engineering menu that allows you to adjust the sensitivity of the sensors. To access it, open the Phone app and type in a special code. This is safe and does not require root rights.
Once you enter the command, the CIT (Customer Integration Test) menu will appear on the screen. Find the "Proximity sensor" or "Proximity Sensor" item in the list. You will be asked to close the top of the screen with your hand (the sensor should show a value of 5.0 or "Near") and remove your hand (a value of 0.0 or "Far"). Press the "Calibrate" button to write the new reference values.
After successful calibration, be sure to restart the device, which is necessary for the MIUI system to apply new hardware parameters. If after the reboot the problem persists, you can try resetting the sensor to the factory settings in the same menu, if this option is available in your version of the firmware.
☑️ Checklist of sensor calibration
Set up system parameters and clean up the cache
Sometimes the problem is the accumulated garbage of system applications. Clearing the cache of the service "Phone" and "Contacts" can eliminate the software conflict. Go to Settings → Apps → All applications, find "Phone" and select "Clear cache." Similar procedure repeat for the application "Contacts".
Note the Pocket Mode feature. In some versions of MIUI, it can be too aggressive, locking the screen whenever you move in your bag or pocket. Turn off this option in your lock settings to see if it affects the sensor's performance during calls, which will help to eliminate software error from the security algorithms.
Also, check whether the "Loudening in your pocket" or similar audio enhancement options that may conflict with sensors are enabled. In Settings → Sound and Vibration, turn off all experimental functions. After each change, check if the screen goes out when you bring it to your ear.
What to do if the engineering menu code doesn’t work?
Table: Comparison of methods of solving the problem
For ease of perception, we have systematized the basic methods of troubleshooting, choose the one that best suits your situation and level of technical training.
| Method | Difficulty | Efficiency | Risk of data loss |
|---|---|---|---|
| Cleaning the sensor | Low. | Medium | No. |
| Calibration via CIT | Medium | Tall. | No. |
| Resetting settings | Tall. | Maximum | Total loss. |
| Glass replacement | Tall. | Depends on the cause. | No (if careful) |
Radical measures: Resetting and updating software
If the software settings didn’t help, there may have been some critical errors in the system, in which case a full factory reset helps, and before that, be sure to back up all important data, as formatting will delete all files, photos and contacts from the device’s internal memory.
Check for system updates. Xiaomi developers regularly release patches to fix sensor errors. Go to Settings → About Phone → MIUI Version and click "Check Updates." If a new version is available, install it by pre-charging the battery to at least 60%.
⚠️ Note: Before performing a full reset, make sure you remember the password from your Mi Account and Google account. Once reset, the phone will require them to prove ownership, and without this data, you will not be able to use the device.
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Hard Reset eliminates 95% of sensor-related software errors, but takes time to recover data and reconfigure applications.
Hardware problems and sensor repair
In rare cases, the problem is physical. In the Redmi 9C, the proximity sensor is soldered into or near the display plume, and if the phone falls or is exposed to moisture, the contact may oxidize or move away, and visually, it's difficult to determine, it requires disassembly of the device.
If the screen goes out chaotically, even when you're not holding the phone in your hands, and the calibration doesn't help, it's likely that the sensor is faulty. In a service center, it can be replaced or soldered. Self-repair is not recommended, as you can damage the display plume, which will lead to more expensive repairs.
A temporary solution for hardware failure may be to use third-party applications to manage calls that lock the screen programmatically, ignoring the sensor readings. However, this is only a “crutches”, and for full work it is better to consult specialists.
⚠️ Warning: Do not try to disassemble your smartphone yourself if it is under warranty. Violation of seals will lead to denial of free service. If you suspect a defect, immediately carry the device to an authorized center.
Can the proximity sensor be permanently disabled?
Additional Tips for Operating the Redmi 9C
To avoid future sensor problems, try to keep the device from overheating. High temperatures can affect electronics, causing false alarms of sensors. Also avoid using magnetic holders in a low-quality car, strong magnets can work Hall sensors and approach.
Check the condition of the protective coating regularly. If there are chips on the glass at the top, it is better to replace it. Cracks can let moisture or dust into the body, which will eventually lead to corrosion of the sensor contacts. Careful attitude will prolong the life of your Xiaomi.
Keep an eye out for updates to the Phone and Contacts apps on Google Play. Often Google releases patches for its services that affect basic call functionality. The latest version of the software is the key to the stable operation of the entire system.
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Regular prevention, including cleaning the speaker and software updates, reduces the risk of proximity sensor problems by 80%.