Checking the proximity sensor Xiaomi Mi Mix 2s

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Xiaomi Mi Mix 2s is known for its unique design, devoid of an upper bezels, which has created serious engineering challenges for developers. One of the most common problems of this model is the incorrect operation of the sensor responsible for locking the screen during a conversation. Users often face a situation where the screen does not go out when holding the phone to the ear, which leads to accidental cheek presses and interruptions.

In this article, we will discuss in detail how to diagnose and troubleshoot this module, the proximity sensor in this model is located at the top of the case, hidden under the glass, and its operation depends on many software and hardware factors, and understanding how it works will help you identify the cause of the failure.

For starters, the problem can be both software-based and physical, and service center statistics show that a large proportion of complaints are resolved without replacing components, by simply calibrating or resetting, but ignoring symptoms can lead to more complex breakdowns.

The operating principle and location of the sensor in the Mi Mix 2s

Unlike classic smartphones, where the infrared emitter and receiver are in the visible part of the upper bezels, in the Mi Mix 2s they are hidden. Engineers used ultrasonic sound technology and a miniature sensor integrated into a narrow strip above the display. This solution allowed to increase the screen area, but made the device more sensitive to contamination and software conflicts.

The infrared sensor is constantly emitting invisible radiation and reading the reflected signal. When you hold the phone to your head, the distance to the object is reduced, and the intensity of the reflected signal changes, which tells the system to extinguish the display. Any obstacle, even a thin film or a greasy trail, can distort this reading.

⚠️ Attention: The use of thick protective glasses or glasses with a black frame that covers the upper part often causes false alarms of the sensor.

It is important to understand that the Xiaomi Mi Mix 2s does not have a physical button or visible hole for this sensor in the usual sense. The entire upper part of the body is a work area, and the presence of any foreign objects in this area is unacceptable for the correct operation of the system proximity.

Symptoms of malfunction and primary diagnosis

Before we go to complex engineering menus, we need to clearly identify symptoms, and it's not always a black screen that means a malfunction when you call, and sometimes it's the result of a malfunction in the MIUI operating system or a conflicting application.

The main sign of a malfunction is that the screen doesn't react to the approach of your hands or objects. You can do a simple test: make a test call and slowly hold your palm to the top of the screen. If the display doesn't go out and light up when you remove your hand, you need to intervene.

There are a number of characteristic signs indicating problems with the module:

• 📞 The screen does not turn off during a conversation and you accidentally hit the reset or volume button with your cheek.
• 🌑 The display goes off immediately after the call starts, even if the phone is lying on the table and nothing covers the top of the phone.
• 🔦 The notification indicator (if active) behaves strangely or does not light up when an incoming call is made.
• 📉 Fast battery discharge due to a constantly running screen during.

If you see any of these symptoms, you need to do a deeper check through the system menu, which will separate the software glitch from the physical breakdown.

Using the CIT Engineering Menu to Check

The most reliable way to diagnose is to use the built-in CIT (Customer Integration Test) menu, which is available on all Xiaomi smartphones and allows you to test each hardware component separately from the main operating system.

You don't need a superuser or a computer connection to log into the diagnostic menu, but you just need to type in a special combination of characters in the Phone app, which is the safest and fastest method of initial iron assessment.

Follow the following steps to start the test:

1. Open the standard call app.
2. Enter the code ##6484## or #64663###.
3. In the list you can find Proximity Sensor.
4. Close the top of the screen with your hand and remove it while watching the readings on the screen.

In the test mode, you'll see numerical values or a graphical indicator. When the hand closes the top, the value should change (usually from 5.0 to 0.0 or vice versa, depending on the firmware version), if the values do not change or change randomly, this indicates a problem.

⚠️ Note: Do not click on the Fail or Pass button in the engineering menu if you are not sure of the result, as this may record false statistics in the device’s log files.

Calibration of the sensor through the hidden menu

Oftentimes, the sensor is physically functional, but it's calibrated wrong, and this can happen after a display change, a device drop, or a failed firmware update, and then forced calibration will help.

The calibration process requires precision. You need to ensure that the top of the screen is perfectly clean and that there are no infrared sources nearby (like direct sunlight or incandescent lights). Calibration is the process of putting zero points on the sensor.

Calibration instructions:

• 🧹 Wash the top of the screen with microfiber.
• 📱 Place your phone on a flat horizontal surface.
• 🛠 On the menu. CIT Click on three dots (or the Menu button) and select "Calibration».
• ⏳ Do not touch the phone until the process is complete (usually). 10-15 seconds).

Once the procedure is completed successfully, the device will automatically restart or ask to do it manually, and if the calibration fails, it may be a hardware problem that requires disassembly.

Table of codes and sensor status values

In the case of an engineering menu or ADB-You may encounter different numerical values, and understanding their meaning will help you determine the nature of the malfunction more accurately.

If you see a value of -1.0, it almost guaranteed to indicate a physical disconnect between the motherboard and the sensor. 90% of the time on the Xiaomi Mi Mix 2s, this is solved by soldering the plume or replacing the module.

For advanced users, verification is available through ADB-So if you connect the phone to a PC, you can type in the adb shell dumpsys sensor to see the raw data from all the sensors in real time, and that allows you to track the micro-latency in the sensor response.

Software solutions and resetting settings

If the hardware is fine but the problem persists, the culprit may be a software conflict.The Android operating system or MIUI shell may not process sensor signals properly.

The first step is to update all system components through the Security app or phone settings, and often manufacturers release patches that fix drivers.

List of actions for programmatic correction:

• 🔄 Update the system to the latest available version.
• 🗑 Clear the cache of the “Phone” and “Contacts” application».
• 🚫 Turn off the “Respond with Motion” function in call settings.
• 📵 Check if the antivirus or call recording app is blocking access.

In extreme cases, if nothing helps, you can perform a full reset to factory. Hard Reset will delete all data, so pre-create a backup of important information.

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Before performing a complete reset, be sure to remove SIM-card and memory card to avoid accidental formatting or file system damage.

Hardware causes and physical repairs

When software methods are exhausted, there is a possibility of physical damage. In the Xiaomi Mi Mix 2s, the proximity sensor often fails after falls or moisture, and the cause can also be a departing plume.

Disassembly requires caution, because the back cover is glued and there are many fragile plumes inside, and the sensor itself can be soldered on the display plume or be a separate module, depending on the revision of the board.

Main hardware problems:

1. Mechanical damage to the sensor crystal.
2. Oxidation of contacts due to moisture.
3. A break in the plume connecting the sensor to the motherboard.
4. Poor assembly after previous repair (clamped plume).

⚠️ Attention: Independent disassembly Xiaomi Mi Mix 2s Inexperienced intervention can damage the display or camera plumes.

If you don't have soldering and small electronics skills, you should go to a specialized service, and replacing the sensor or plume is an inexpensive procedure, but it requires a professional tool.

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In most cases, the problem is solved by calibration or cleaning, but if the phone falls, a physical defect in the component is likely.