Owners of Xiaomi smartphones often face a situation when during a conversation the screen goes out prematurely or, conversely, the cheek presses the dial buttons. In the Redmi Note 9 Pro model, a special sensor located at the top of the display is responsible for this function. Its incorrect work can turn a regular call into a real test, forcing the user to complete calls with a hands-free connection or constantly wipe the screen.
Diagnosing this component is the first step to solving a problem, and users often confuse a software failure with a physical failure, although in most cases simple calibration is enough, and understanding how the system works allows you to quickly identify the source of the malfunction and fix it without going to the service center.
In this guide, we will take a look at all the test methods available, from embedded engineering codes to third-party applications, learn how to distinguish software errors from mechanical damage and learn how to properly adjust the sensitivity of the sensor for comfortable use.
Principle of operation and location of the sensor
The technology used in the Redmi Note 9 Pro is based on infrared radiation, and the sensor emits an invisible beam and reads its reflection from objects. If the beam reflects, the system recognizes that the phone is in the ear, and turns off the touchscreen. In this model, the component is hidden under the display glass, making it less visible but more sensitive to contamination.
The main purpose of the device is to prevent accidental tapping of the cheek or ear during a conversation. The infrared port is paired with the MIUI shell software. When an incoming call arrives, the system polls the sensor several times per second. If the object is closer to 2-3 centimeters, the screen is locked.
The location of the sensor at the top of the screen, next to the speaker, dictates certain requirements for accessories. Protective glass with a thick frame or poor-quality cases can overlap the work area, causing false positives. It is important to make sure that the area above the speaker is clean and not closed with foreign objects.
⚠️ Warning: Using thick, black-framed protective glasses is the most common cause of problems. The frame can block the IR emitter, making the phone think it's in the ear all the time.
Understanding the physics of the process helps in diagnosis, so if you put your finger up to the top of the screen and it goes out, the mechanism works, and if you don't react even when you press it tightly, it may be that the component is out of order or that it's contaminated from the inside.
Diagnostics through the Engineering Menu
The most reliable way to check the condition of the equipment is to use the built-in CIT engineering menu, which is available on all Xiaomi devices and allows you to test each module separately, and you do not need root rights or a computer connection to run the diagnostics.
You open the standard Phone app and dial a special character combination, and once you enter the last digit, the menu will open automatically, and here's a complete list of tests, from the screen to the vibrator.
##6484##The list that opens will show you the item associated with the Proximity Sensor, which is usually at the top of the list or in a section labeled "Single Item Test," and you click on it and you'll be in real-time mode, where you'll see the current readings.
☑️ Checking in CIT menu
In the test mode, you'll see a digital value. When the hand is removed, the value should be 5.0 (or close to 0 in some versions, but more often 5.0 means "far away"). When you cover the top of the screen with your palm, the value should change to 0.0 ("close"). If the numbers don't change or change randomly, this indicates a problem.
Using the code to check for approximation
There is an alternative, faster code that immediately runs a test of a particular module, bypassing the main menu of engineering verification, which is convenient if you need to quickly assess the situation without unnecessary clicks on the menu.
##7726##Entering this combination in the Phone app immediately switches the device into proximity sensor check mode. The screen can go out or change color, which is normal behavior. In this mode, the system ignores other touches, focusing only on the reaction of the top edge of the display.
For proper verification, follow the following steps:
- 📱 Close the upper third of the screen where the speaker is located.
- 👀 Watch the reaction: the screen must react instantly.
- 🔄 Remove your hand, the screen should light up again.
- 📉 If there is no reaction, try to wipe the speaker area with an alcohol napkin.
It's important to test in bright light to see the changes on the display, and if the sensor is perfect in this mode and it's buggy in normal calls, the problem is with the system settings or third-party apps blocking the screen.
⚠️ Warning: During the test, the phone may get very hot at the top.This is normal for diagnostic mode, but don't keep the test running for longer. 2-3 momentarily.
Third-party testing applications
If the built-in methods don’t seem informative enough, you can use third-party software from Google Play. These utilities often provide a more detailed schedule of changes and reading history, which is useful for identifying intermittent problems (when the sensor is working, it is not).
One popular solution is the Proximity Sensor Test or Sensor Test app from various developers, which displays raw sensor data in the form of numbers or color indicators, green usually means "no object", red - "object nearby".
Why can third-party apps show other data?
The advantage of these programs is that they can calibrate, and some of them allow you to set a sensitivity threshold if you don't like the standard settings of Xiaomi, but it's worth remembering that deep calibration requires caution.
When choosing an app, pay attention to permissions. Testers don't need access to contacts or a microphone, only access to sensors. Avoid installing questionable programs with a lot of advertising.
Calibration of the sensor on the Redmi Note 9 Pro
If the diagnostics show that the sensor is responding but not correctly (e.g., extinguishing the screen 5 cm before the face), calibration is required, which resets the reference distance values stored in the device's memory.
Calibration is also done via the ##6484## engineering menu. Find the Proximity Sensor and click the Calibration button. Make sure there is nothing in front of the screen before you start.
Step instructions:
- Place the phone on a flat surface with the screen up.
- Make sure there are no objects above the screen, including hands.
- Click the “Start” or “Calibrate” button in the test menu.
- Do not touch the phone until the process is complete (usually 5-10 seconds).
- After the message “Success” restart the device.
| Symptoms. | Possible cause | Method of decision |
|---|---|---|
| The screen doesn't go out when you ring. | Pollution or software failure | Wipe and calibration |
| The screen goes out in your pocket | High sensitivity | Resetting calibration |
| Phone drops calls | Constant “sticking” of the sensor | Checking the protective glass |
| No reaction to the arm. | Physical breakdown | Replacement of module in the service |
💡
Calibration should only be done on a clean device lying on a table, and the presence of hands or objects nearby will distort the reference values.
After the reboot, be sure to check the sensor on a real call. If the problem persists, you may need to reset to factory settings, but this is a last resort.
Problems and frequent errors
Even after calibration, there can be situations where the Redmi Note 9 Pro is acting strangely, often unseen factors are the culprits, such as static electricity accumulating on the screen can interfere with the IR beam, and regular wet cleaning of the screen helps solve this problem.
Another common mistake is installing smart cases with a magnetic fastener or thick back wall that deform the body at the top, and the pressure on the frame can be transferred to the internal components, displacing the sensor.
What else can get in the way:
- 🌡️ Overheating of the device: at high temperatures, sensors can work unstablely.
- 📲 Conflicting applications: Memory cleanup programs or “battery savers” can block sensor performance.
- 💾 Covered system cache: Clearing temporary files sometimes returns sensitivity.
If nothing works, it's worth checking if the protective glass at the top has unstuck, and even a microscopic gap can refract the beam incorrectly, in which case only a replacement glass or professional pasting will help.
⚠️ Warning: Do not use chemical solvents (acetone, gasoline) to clean the sensor area.They can damage the oleophobic coating and make the plastic glass speaker cloudy, which will worsen the sensor performance.