Owners of Xiaomi’s flagship smartphones often face a situation where the screen does not go out during a conversation, and important calls are dropped with the cheek or a loud communication is accidentally activated. This is a classic sign of a failure in the approach sensor, which in the Mi 9 Pro model has its own specific location and design. Understanding exactly where this sensor is located is critical for the proper diagnosis, cleaning or calibration of the device.
Unlike budget models, where the sensor is often displayed in a separate hole in the upper frame, Xiaomi Mi 9 Pro engineers used technology hidden placement under the display glass. This solution allows you to maintain the aesthetic appearance of the front panel without unnecessary cuts, but makes the device more sensitive to the quality of protective films and the cleanness of the screen.
If you notice that the phone is not behaving correctly during calls, you should not immediately carry it to the service center. In most cases, the problem is solved by software calibration or simple cleaning of the sensor area from contamination. Next, we will discuss in detail the design features, testing methods and ways to eliminate software failures that interfere with the correct operation of the distance sensor.
Design features of the sensor in Xiaomi Mi 9 Pro
The Mi 9 Pro is a frameless device that dictates its own optical environment, and the proximity sensor is an infrared emitter and receiver hidden under a layer of display, requiring high transparency of materials and fine-tuning of the software algorithms that determine when the touchscreen is turned off when the phone is held to the ear.
The physically active area of the sensor is located in the upper center of the screen, occupying an area about 1-1.5 centimeters wide under the speaker. It is in this area that infrared radiation passes through the display glass. Any foreign objects, including thick protective glasses with a black frame, can block the path of the rays, causing a false alarm or, conversely, ignoring the proximity of the object.
Importantly, this model uses a combined system where the light sensor often pairs with the proximity sensor, but their physical reading points may differ slightly. A single element's malfunction often affects the overall screen control algorithm during a call. Understanding this relationship helps to better diagnose the problem: if the automatic brightness is also not working correctly, the problem may lie in the contamination of this upper region.
💡
Use only protective glass with a cutout for sensors or completely transparent at the edges, so as not to block the IR radiation of the sensor.
Exact location and sensitivity area
To successfully calibrate or manually verify, you need to know the exact geometry of the sensitive zone. In the Xiaomi Mi 9 Pro, this area is invisible to the eye when turned off, but its coordinates are rigidly specified in the firmware. The center of the sensitivity zone coincides with the center of the upper end of the device, just below the metal frame of the case.
If you draw a conventional vertical line from the center of the speaker down the screen, there will be an active point of the optical sensor at a distance of 5-10 millimeters. When you apply your finger to this area during an incoming call, the screen should immediately go out. If this does not happen, or the screen goes out when you press other parts of the display, you need to adjust the parameters.
Often users mistakenly paste this area with stickers or allow dust to accumulate in the speaker grid, which indirectly affects the work of neighboring elements. The purity of the glass in the upper third of the screen is a prerequisite for stable operation. Dirt or greasy spots in this area can scatter the infrared beam, creating the effect of "constant proximity" of the object.
Diagnostics of performance through the engineering menu
Before you start complex manipulations, you need to run a hardware test, and the MIUI has a special diagnostic module built in to test the response of all sensors without installing third-party software, and this is the most reliable way to determine whether a problem is a physical failure or a software failure.
To run the test, you need to open the Phone app and enter the universal code ##6484##. Once you enter the combination, the CIT menu will open. In the test list, you need to find the "Proximity Sensor" or "Approximation Sensor" item. When you click on it, you will be taken to the diagnostic window, where the current state of the sensor will be displayed.
In the test mode, the screen will change color or show the distance in centimeters. Hold your palm to the top of the screen (2-3 cm) and remove it. If the values change (for example, from 5.0 cm to 0.0 cm or the status changes from Far to Near), then the sensor is physically healthy and the problem lies in the calibration. If there is no reaction at all, there is a possible hardware defect in the plume or module itself.
☑️ Sensor diagnostics
Procedure for program calibration of the sensor
If testing shows that the sensor is responding but is not doing so correctly (e.g., turning off the screen too soon or too late), calibration is required, which trains the memory controller to set the correct trigger thresholds for your particular device instance.
When you're in the sensor test menu (described in the previous section), press Calibration or Calibration. The system will ask you to remove your hand from the screen to record the "far" state, then completely close the top of the screen with your palm, leaving no gaps, and confirm the action.
Once successfully calibrated, the phone can automatically restart or suggest restarting the device manually, which is necessary to apply new parameters to the system configuration files. Ignoring the reboot can cause the old settings to remain in the cache and the problem will not go away.
⚠️ Warning: During calibration, make sure there is no thick edge protective film on the screen, otherwise you will calibrate the sensor to take into account the obstacle and it will not work properly after it is removed.
Hardware causes of malfunctions and their elimination
In the case when software methods do not help, it is worth considering physical factors. Xiaomi Mi 9 Pro has a complex internal layout, and sometimes the sensor plume can move away from the connector of the motherboard after falls or vibrations.
A common cause of false positives is poor-quality protective glass. If the black glass frame covers even a millimeter of the sensor's active zone, the phone will think that it is constantly in the ear, in which case it helps to neatly scrape the black paint from the inside of the glass in the sensor area or replace the accessory with a more suitable one.
The table below shows the main symptoms and probable causes of malfunctions:
| Symptoms. | Probable cause | Method of decision |
|---|---|---|
| The screen doesn't go out when you ring. | Glass contamination, calibration failure | Cleaning, calibration through CIT |
| The screen goes off immediately when dialing | The security glass override the sensor | Glass replacement, film removal |
| No reaction to the arm in the test | Trail break, module malfunction | Replacement of the plume, repair in the SCC |
| Chaotic screen switching on | Programmatic conflict, MIUI bug | Resetting, flashing |
If you suspect a physical breakdown, such as a plume drifting away, self-opening of the device is not recommended without experience and tools, as you can damage the fragile plumes of the display or disrupt the tightness of the case.
Can I turn off the proximity sensor completely?
Impact of MIUI Updates and Third Party Launchers
Sometimes the problem arises after an operating system update. New versions of MIUI may contain bugs in sensor control drivers. In such cases, users often report massive problems on forums. Checking the history of updates and reviews of other Mi 9 Pro owners helps to determine whether the problem is global for the current version of the software.
Also consider the impact of installed launchers and call management applications. Third-party callers may have their sensor signal processing priority conflicting with the system one. If the problem occurs after installing a new application, try removing it or checking your hardware access settings.
In rare cases, a full reset to factory settings (Wipe Data) helps, but before that, be sure to back up all important data. This eliminates software conflicts in the system configuration files that could accumulate during the use of the smartphone.
💡
90% of sensor problems are solved by cleaning the top of the screen and recalibrating through the engineering menu, without the need to replace parts.