Xiaomi’s Redmi 9 series is well-deservedly popular for its excellent price-performance ratio, but even reliable devices can cause hardware failures. One of the most annoying problems for users is the incorrect operation of the proximity sensor, which is responsible for cancelling the screen during a conversation. If the screen does not turn off when you hold the phone to your ear, you can accidentally press the end button or launch an unnecessary application, which leads to interruption of communication or unnecessary costs.
In this article, we will take a look at how to test the proximity sensor on Redmi 9 using built-in system tools and special engineering codes, how to distinguish a software failure from a physical failure, and get step-by-step instructions for calibrating the sensor without going to the service center.
Before we start a deep diagnostic, it is important to understand that in the Redmi 9, this sensor is located at the top of the front panel, often hidden under the black bezel of the display. Pollution of this area, the use of poor-quality protective glasses or banal dust can cause false positives. Testing the sensor is the first step that must be done before you suspect the failure of expensive components of the board.
Primary visual and physical diagnostics
Before diving into complex menus and codes, you need to rule out the most common causes of malfunction, which occur in 80% of cases. Often users forget that the protective film or glass can overlap the sensitive element, especially if the accessory is not matched to a particular model or is skewed. Carefully examine the top of the screen when the display is turned off: the sensor area usually looks like a dark spot next to the speaker.
Clean the top of your smartphone with a soft, slightly moist microfiber fabric. Fat spots from your fingers or contamination in the speaker area can distort the infrared radiation that an infrared sensor uses to determine the distance to an object. If after thorough cleaning the problem persists, remove the protective glass and check the module's operation in a "clean" form.
⚠️ Note: Do not use aggressive chemical solvents or alcohol in large quantities to clean the sensor area, as liquid can leak under the display frame and damage the plumes.
Also worth noting is the case. Some silicone or leather cases have too high sides that can partially overlap the sensor's area of operation. Take off the case and see if the screen's response to the arm's approach has changed. If the physical integrity of the device is intact and the screen has no cracks in the top, you can proceed to software tests.
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Use a flashlight to illuminate the sensor area at an angle: if you see a small black window that doesn’t glow like a camera, you’ve found the right piece.
Using the CIT Engineering Menu for Testing
The most reliable way to test the proximity sensor on Redmi 9 is to use the built-in CIT (Customer Integration Test) engineering menu, which is designed for factory diagnostics and allows you to check each hardware module separately, without third-party applications, accessed through a special menu of the phone, which is hidden from the average user.
To enter the test mode, open the standard Phone app and enter the universal code ##6484#. If the code is entered correctly, the system will automatically redirect you to the CIT menu, where you will find a list of all the components of the device.
In the window that opens, you will see the numerical value and color indication. When your hand is removed from the screen, the value should be close to 5.0 or displayed in green. When you hold your palm to the top of the screen (at a distance of 2-3 cm), the value should change, and the indicator should turn red or show "Near".
☑️ Checking in CIT menu
If the CIT sensor works perfectly (values change instantly and clearly) but the screen does not go out in normal calls, then the problem lies in the software conflict or system settings, not in the hardware.
Secret codes and additional verification methods
In addition to the main CIT menu, there are alternative ways to enter diagnostic modes in the MIUI shell that can be useful if the standard code fails or is blocked by the operator. One such method is using the code ##4636##, which opens the Testing menu, although it is more often used to check the network and battery, in some versions of the firmware there you can find advanced information about the sensors.
Another option is to use the Service & Feedback app, which is pre-installed on all Xiaomi smartphones, and go to Check device inside the app, which is more user-friendly because the interface is fully translated and adapted.
There is also a method of checking through the hidden engineer menu, available through the settings:
- Go to Settings. → The phone.
- Quickly click on the "Kernel Version" or "MIUI Version" option several times until a message appears to turn on the developer mode (although this is more for debugging over USB, sometimes opens access to logs).
- More direct: In the Phone app, type ##64663## (works on some regional versions).
⚠️ Warning: Be careful when changing your settings in the engineering menu, do not click on the "Clear Data" or "Reset" buttons, if you are not sure about your actions, this can reset important network settings.
If none of the codes work, your firmware version may have limitations.In this case, it is recommended to download the official Xiaomi app. ADB/Fastboot Tools on the computer, but it already requires a PC and USB-cable.
Procedure for calibration of the proximity sensor
If the diagnostics show that the sensor is responding but with a delay or incorrectly (for example, the screen is only turned off point-blank), the sensor must be calibrated. This procedure "trains" the memory controller to correctly determine the threshold values of distance. On Redmi 9, calibration can be done in two ways: through the CIT engineering menu or through a special application.
The method through CIT (checkout menu):
1. Enter the CIT menu with ##6484##.
2. Select "Proximity sensor".
3. In the top corner of the screen (usually on the right or left), find the "Calibration" or "Calibration" button.
4. Follow the instructions on the screen: first remove your hand from the sensor and press "OK", then close the sensor with your palm and press "OK" again.
5. Upon successful completion, the message "Calibration Success" will appear.
The second way is to use the Approximation Sensor (often called Proximity Sensor Reset or similar) app, which you can find in the Google Play directory. These apps automate the command-entry process. Once installed, launch the app, put the phone on a flat surface without covering the top, and click Calibrate.
| Calibration method | Difficulty | Demands a PC. | Efficiency |
|---|---|---|---|
| Through the CIT menu | Low. | No. | Tall. |
| App from Play Market | Low. | No. | Medium |
| Through ADB teams | Tall. | Yes. | Maximum |
| Resetting settings | Medium | No. | Depends on the case. |
After calibration, be sure to restart the device.Reboot is a critical step, since new values of sensitivity thresholds are recorded in the controller’s memory only after a full cycle of switching off and on the power.
Program conflicts and system settings
Sometimes the hardware is good, but the software conflict keeps the sensor from working properly. There are settings in the MIUI shell that can affect the screen. First of all, check if the In-Pack mode is on. This feature is designed to prevent accidental taps, but when using dense cases, it can block the sensor.
Path to setup: Settings → Lock screen → Mode in your pocket. Try turning off this switch and check the phone's performance in the call. Also worth paying attention to the design topic. Third-party themes downloaded from Themes store may contain code errors that disrupt the system sensors. Switch to the standard theme "Classic" or "Default" for verification.
Another reason could be background apps that intercept screen control, like if you've recently installed call management apps, conversation recordings, or smart blockers, or try to run your phone into Safe Mode (press the off button, then keep your finger on the off button on the screen for a long time) to turn off all third-party apps, and if the sensor is working perfectly in safe mode, one of the apps installed is to blame.
What is a safe regime?
Also, don’t forget the trivial system update. In About Phone → MIUI, check for updates. Xiaomi engineers regularly release patches that fix sensor errors in new versions of Android.
Radical measures: dumping and hardware repairs
If neither calibration nor settings checks work, there are two options: a full data reset or a service call. A hard reset will remove all the software errors that have accumulated in the system, but with them your photos, contacts and applications will disappear. Before that, make sure to back up your data to the Mi Cloud cloud or your computer.
To reset, go to Settings → About Phone → Settings Reset → Clear all data. Once the process is complete, the phone will look like new. If the proximity sensor on Redmi 9 is not behaving correctly after that (does not go out when you bring it to your face or, on the contrary, it goes out on its own), the probability of hardware failure is 99%.
Hardware breakdown may be related to:
- 📱 Sensor plume departure from the motherboard (often after falls).
- 💧 Oxidation of contacts due to moisture.
- 🔌 Failure of the sensor module (requires replacement).
- 🛠 Display plume damage, as in Redmi 9, the sensor is often integrated into the screen plume.
⚠️ Attention: Self-disassembly of the Redmi 9 requires skills and tools. The back cover is glued and the plumes are very thin. Inept intervention can cause the plume to rupture and the phone to fail completely.
In case of hardware problems, it is recommended to contact an authorized service center. Replacing a sensor or plume is a quick procedure and usually not expensive, especially compared to buying a new device.
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If after resetting to factory settings and checking in CIT-The sensor does not respond to the menu, the problem is physical and requires a replacement of the component in the service.