Where is the proximity sensor in Xiaomi Mi 9: location, functions and diagnostics

The Xiaomi Mi 9, launched in 2019, has become one of the brand’s flagship devices with top-end specs. However, even such advanced gadgets are not immune to minor problems such as proximity sensor problems. This tiny but important element is responsible for automatically turning off the screen during a conversation, preventing accidental tapping of the cheek or ear. If the sensor fails, users face unpleasant consequences: the screen does not go out when you call, buttons are accidentally pressed, and the battery is discharged faster due to constant lighting.

In this article, we will discuss in detail where the proximity sensor in the Xiaomi Mi 9 is located, how it works, what signs indicate it is malfunctioning, and what to do if the sensor has ceased to function correctly. You will also learn how to independently check the sensor’s performance without going to the service center, and what precautions will help to avoid its failure in the future.

Where is the proximity sensor in Xiaomi Mi 9: the exact location

In the Xiaomi Mi 9, the proximity sensor is integrated into the top of the screen, next to the speaker for conversations and the front camera, specifically located under the display glass, to the left of the selfie camera, in the area of the so-called "bangs" (cutout at the top of the screen), this is a typical solution for most smartphones with a frameless design, where manufacturers seek to minimize the free space on the front panel.

Physically, the sensor is a miniature infrared sensor that emits and picks up the reflected signal. When you hold the phone to your ear, the signal bounces off the surface (like the skin) and back, which serves as a command to turn off the screen. The Mi 9 uses STK3311, a popular chip from Sitronix, which is also found in other flagships of the period.

• 📍 Exact location: under glass, left of front camera (on the speaker side).
• 🔍 External signs: there are no visible holes on the screen - the sensor is hidden under the display.
• 🛠️ Access for repair: requires screen removal, as the sensor is soldered to the display plume.

It is important to understand that the proximity sensor in the Mi 9 is not a single module, but part of a single display plume, which means that if it breaks, you can’t replace the sensor alone: you have to change the entire display module or plume assembly, which is why repairs are expensive, and many service centers offer alternative solutions (for example, disabling the sensor software).

How the proximity sensor in Xiaomi Mi 9: the principle of operation

The proximity sensor in the Xiaomi Mi 9 operates on the basis of infrared radiation. Its work can be divided into several stages:

1. Sensor emits infrared waves constantly within a small radius (usually 2-5 cm from the screen).
2. The signal reflection. When you hold your phone to your ear or other object, the waves bounce back.
3. Data analysis: The sensor chip picks up the signal it's returning and sends the command to the processor.
4. Turn off the screen. The system turns off the backlight of the display and blocks touch taps.

In the Mi 9, not only the sensor itself, but also the MIUI firmware, are responsible for processing the sensor signals, which is why after updating the system, some users encounter bugs in the sensor’s operation — for example, the screen does not go out or, on the contrary, turns off too early, this is due to incorrect calibration of the software, not physical failure.

Interestingly, the Mi 9 pairs the proximity sensor with a light sensor that is also located at the top of the screen, and these two sensors are often confused because they perform similar functions (responsible to external conditions), but the light sensor is responsible for automatically adjusting the brightness, not turning off the screen during a call.

💡

If the proximity sensor is activated too early (the screen goes out at the slightest approach of the hand), try calibrating it through the engineering menu. To do this, dial ##6484## and select Proximity Sensor.

Signs of malfunction of the proximity sensor

The Xiaomi Mi 9's proximity sensor is not working properly, and there are several symptoms to be learned, and it's important to distinguish between software failures and hardware failures, as the ways to fix them are fundamentally different.

Main signs of malfunction:

• 📵 The screen doesn't go out when you call, and the most obvious symptom is that the display stays active when you hold the phone to your ear, which leads to random taps.
• 🔄 The screen goes out too soon, like just holding the phone in your hand or tilting it a little.
• 🔋 If the sensor constantly thinks something is coming, it forces the system to continuously process the signals, which increases power consumption.
• 🛠️ Artifacts on screen. In rare cases, a faulty sensor can cause backlight flickering or spontaneous pressing.

You also need to look at how the phone behaves in different environments, for example, if the sensor is working normally in a dark room but starts to glit in the bright sun, the problem may be that the IR sensor is contaminated or that the sensitivity is not properly adjusted, and if the symptoms are constantly on, regardless of the light, it's likely that the hardware is broken.

⚠️ Warning: If the sensor stopped working after a fall or hit the phone, do not try to disassemble the Mi 9 yourself! In this model, the display plume is extremely fragile, and careless actions can lead to damage to the matrix or touch panel.

How to check the proximity sensor on Xiaomi Mi 9

Before you bring your phone to the service, you can diagnose the proximity sensor yourself, and there are several methods for doing this, from simple tests to using an engineering menu.

Method 1: Testing by dialing a number

The fastest way to check the sensor is:

1. Open the Phone app and dial any number (do not press "Call").
2. Hold your hand or finger to the top of the screen (where the sensor is located).
3. If the screen goes out, the sensor works. If it doesn't, move on to the next method.

Method 2: Engineering menu

More accurate diagnosis is available through a hidden menu:

1. Open the phone app and dial the combination: ##6484##.
2. Select Proximity Sensor (approximation sensor).
3. A graph or digital value will appear on the screen (usually 0 is nothing found, 1 or 5 is an object nearby).
4. Put your hand in the sensor, the value should change, and if it doesn't, the sensor is defective.

Check the screen reaction when calling|Run the test with #6484##|Test the sensor in a dark and light room|Make sure there is no dirt or protective film on the sensor-->

Method 3: Applications for testing

Google Play has tools that allow you to test all the sensors on your smartphone, like Phone Doctor Plus or Sensor Test, and these programs show the current values of the proximity sensor in real time, which helps detect unstable work.

If all the tests show that the sensor is not responsive to the approach of objects, the problem is likely hardware, and if the sensor is triggered, but with a delay or incorrectly, the software (for example, downed MIUI settings) is to blame.

Why the proximity sensor breaks down: the main reasons

The proximity sensor malfunctions in the Xiaomi Mi 9 can be divided into two categories: hardware (physical damage) and software (software failures).

Hardware causes

• 💥 Hit or fall, even a minor mechanical impact can damage the plume of the display to which the sensor is connected.
• 💧 The Mi 9 has no official water protection, so condensate or liquid can oxidize the sensor contacts.
• 🔧 Poor repairs. If you've changed the screen or the battery before, the trainer may have damaged the plume or misconnected the connectors.
• 🧴 Pollution of the IR sensor: Dust, fat, or protective film can block the infrared signal.

Programmatic reasons

• 📱 Firmware failure after update MIUI The sensor may not work properly due to driver errors.
• 🧩 Application conflict: Some programs (such as launchers or modified firmware) may interfere with sensors.
• ⚙️ If you had previously manually changed the sensor parameters through an engineering menu, it could lead to unstable operation.

Interestingly, the Xiaomi Mi 9’s proximity sensor sometimes starts to glitches after changing the screen, which is because non-original display modules can come with or without uncalibrated sensors, in which case only a re-replacement with a quality screen helps.

How to fix the proximity sensor: possible solutions

If the diagnostics showed that the proximity sensor in Xiaomi Mi 9 does not work, do not rush to carry the phone to the service.

Programmatic correction methods

1. The simple but effective way is that sometimes the sensor starts working after a normal reboot.
2. Reset. Go to Settings → About Phone → Reset and select Reset all settings (not to be confused with a full reset!) This will return the sensors' factory settings.
3. Calibrate through the engineering menu. Type ##6484##, select Proximity Sensor and follow the instructions on the screen.
4. Update firmware. Check for updates in Settings → About Phone → System Update. Sometimes bugs are fixed in newer versions of MIUI.

Hardware techniques

If the software methods do not help, you will have to resort to more radical measures:

• 🧹 Clean the sensor, gently wipe the top of the screen with a lilac-free wipe dipped in alcohol!
• 🔄 Replacement of protective glass: If the glass is too thick or metallized, replace it with a more suitable one.
• 🛠️ Repairs to the service. If the sensor is physically damaged, it will require replacing the display plume or the entire module. In the Mi 9, it's a complex operation that's best left to the professionals.

⚠️ Attention: Some "masters" suggest that the proximity sensor be disabled software so that the screen does not go out during calls. This is a temporary solution, but it creates the risk of accidental pressing and rapid battery discharge!

💡

If the sensor stops working after falling or getting moisture, self-repair can aggravate the problem.

Frequently Asked Questions (FAQ)