Approximation Sensor in Xiaomi Mi 9T: where is located, how it works and what to do in case of malfunction

The Xiaomi Mi 9T (also known as the Redmi K20 in some regions) has a proximity sensor that automatically shuts down the screen during a conversation. This small but critical detail often causes problems: the screen doesn't go out when you reach your ear, random taps during a call, or the inability to unlock the display after a call is complete. If you experience symptoms like this, the first thing to do is figure out where the proximity sensor in the Mi 9T is located and how to diagnose it.

In this article, we will not only show the exact location of the sensor on the case and under the display, but also explain how it is integrated into the smartphone system. You'll learn if you can replace it yourself, what tools you'll need to do that, and what to do if the sensor doesn't work properly because of software failures. 9T from other Xiaomi models – this will help to avoid errors during repair or configuration.

Xiaomi Mi 9T Anatomy: Where to Look for Approach Sensor

In the Xiaomi Mi 9T, the proximity sensor is built into the top of the display, next to the front camera and speaker. However, unlike many budget smartphones, it is not priced on a separate fee, but integrated into a flexible display plume. This means that when the sensor is damaged, it often requires replacing the entire screen module - it is extremely difficult to buy and install only the proximity sensor separately.

Visually determine its location can be on two grounds:

• 🔍 To the right of the front camera (if you look at the screen) - there is a small hole under the infrared sensor.
• 📱 Under the glass of the display, but not on the matrix itself, but on a flexible printed circuit board (FPC), connects the screen to the motherboard.

For clarity, we give a diagram of the location of the key components of the upper panel of the Mi 9T:

It's important to understand that in the Mi 9T, the proximity sensor is not a separate module, like in the old Redmi Note, it's soldered into a plume along with the light sensor, so when diagnosing a malfunction, both sensors are checked simultaneously, and if the screen does not go out during the call, the problem can be hidden in the sensor itself, and in the damaged plume or connector on the motherboard.

How the proximity sensor in the Mi 9T: technical details

In Xiaomi Mi 9T Infrared proximity sensor (IR proximity sensor, which consists of two key elements:

1. The emitter sends an invisible infrared signal.
2. Receiver – captures the reflected signal and determines the distance to the object (for example, the user’s ear).

When you hold the phone to your ear, the signal bounces back to the receiver. The microcontroller analyzes the delay time and "understands" that the screen needs to be turned off. In the Mi 9T, this process handles a dedicated STK3311 chip (or its analogue), which is also responsible for the light sensor, which is why when one sensor fails, it often "gluts" and the second one.

Specifications of the sensor in the Mi 9T:

• 📏 Response range: 0-5 cm (adjusted programmatically).
• ⚡ Nutrition: 2.8V (from a separate line on the motherboard).
• 🔄 Frequency of the survey: ~10 Hz (depending on firmware).
• 🛠️ Type of fastening: soldered into a flexible plume (replacement requires soldering or replacement of the entire module).

Critical: In the Mi 9T, the proximity sensor doesn’t have a separate connector on the motherboard, it connects through the display plume, which means that if the screen connector is damaged (for example, after a fall), the sensor will stop working even if the sensor itself is working.

Signs of malfunction of the proximity sensor

If the proximity sensor in the Xiaomi Mi 9T is not working properly, you will notice one or more of the following symptoms:

• 📵 The screen does not go out during the call, even when the phone is pressed to the ear.
• 🔄 Spontaneously turning on/off the screen when talking.
• 📱 Automatic locking does not work when the hand approaches the top of the display.
• 🔦 The light sensor has ceased to respond to changes in brightness (often comes "included" with a malfunction of the proximity sensor).
• 🛠️ Message "Approximation sensor not responding"** in the engineering menu.

It's important to distinguish between hardware and software failures, for example, if the screen doesn't go out only in certain applications (like WhatsApp or Telegram), the problem is probably the settings of those programs, not the sensor itself, but if the failure manifests itself in all calls, that's a reason for diagnosis.

⚠️ Attention: In Mi 9T There's a known feature, which is that the proximity sensor can temporarily shut down when you use headphones with a microphone. It's normal behavior, not a malfunction. To return the automatic screen shutdown, turn off the headphones or check the call settings.

You can use the engineering menu to get a good diagnosis.

1. Open the Phone app.
2. Enter the combination: ##6484###.
3. Select the Proximity Sensor.
4. Put your hand to the top of the screen, and the value should change from 5 (far) to 0 (close).

If the values don't change or if there's an error, the sensor is faulty. If there's a reaction, but the screen still doesn't go out, it's the firmware or the system settings.

How to check the proximity sensor without disassembling the phone

Before you disassemble the Xiaomi Mi 9T, try the software diagnostic methods to help determine if the sensor or software problem is to blame.

Method 1: Testing through the Engineering Menu

As mentioned, the combination ##6484## opens the sensor testing menu. Alternative code for Mi 9T: #4636## → Phone information → Equipment check. Here you can see the status of all sensors, including proximity.

Method 2: Diagnostic applications

Install one of these apps from Google Play:

• 📱 Phone Doctor Plus – Checks all sensors, including proximity.
• 🔍 Sensor Test – shows the sensor response in real time.
• 🛠️ CPU-Z — Sensors displays the status of the proximity sensor.

If apps show that the sensor is working but the screen isn’t going out, try:

1. Reset network settings: Settings → System → Reset → Network settings reset.
2. Update the firmware to the latest version (sometimes bugs are fixed in new versions of MIUI).
3. Disable the function of Smart Assistant in call settings (may conflict with the sensor).

⚠️ Note: In some of the firmware for Mi 9T (And especially custom, the proximity sensor can be turned off at the core level. If you're using informal firmware, try to get the stock back. MIUI — That often solves the problem.

Self-replacement of the proximity sensor: step-by-step instructions

If the diagnostics confirm the sensor malfunction and the warranty on the phone is already over, you can try to replace it yourself. However, in the Xiaomi Mi 9T, this is more difficult than in most other smartphones, due to the integration of the sensor into the display plume.

• 🔧 Set of screwdrivers (cross, flat, Torx) T3/T4).
• 🧲 Screen suction cup and mediator (plastic shoulder blade).
• 🔥 Hair dryer or thermo-air station (for softening glue).
• 📱 New display plume with sensor (article: 18051-06-000000-00 analogue).
• 🧴 Isopropyl alcohol (for cleaning contacts).

Step-by-step:

1. Turn off the phone and remove it. SIM-map.
2. Heat the screen edge dryer (~60°C) for 2-3 minutes to soften the glue.
3. Put a suction cup on the screen and carefully separate it from the body, starting at the bottom. Be careful, the plume is very fragile!
4. Disconnect the plume connector from the motherboard (use a plastic blade to avoid damaging the contacts).
5. Remove the metal protection from the top of the plume (twisted with 2-3 screws).
6. Unplug the old sensor (if you are trying to replace it only) or install a new plume entirely.
7. Collect the phone in reverse order, making sure that the plume is not bent.

Important: 90% of the time, replacing the proximity sensor alone in the Mi 9T is impossible without specialized equipment (microscope, soldering station), and it is much easier and more reliable to replace the entire display plume, even if the matrix is working.

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Before disassembling, take a picture of the location of all the screws and plumes. Mi 9T uses screws of different lengths - if you confuse them with places, you can damage the motherboard.

Frequent errors in the repair of the proximity sensor

Even experienced craftsmen sometimes make mistakes when working with the Xiaomi Mi 9T. Here are the most common of them:

• 🔧 Use of inappropriate tools - metal blades scratch the body and damage the plumes. Always use plastic or nylon mediators.
• 🔥 Overheating when removing the screen - if the temperature of the hair dryer exceeds 80°C, you can damage the adhesive base under the battery or melt plastic clips.
• 📱 Incorrect installation of the plume – if the display plume is inserted into the connector is not fully inserted, the proximity sensor will not work, even if the screen is turned on.
• 💧 Liquid on the contacts - isopropyl alcohol must completely evaporate before assembly, otherwise corrosion is possible.
• ⚡ Forget to turn off the battery – when working with plumes, always disconnect the battery to avoid short circuits.

Another common problem is buying a non-original plume, and cheap ones often have incompatible proximity sensors that either fail or are delayed. 9T:

• Original: 18051-06-000000-00 (Xiaomi).
• Quality analogue: LCD-FPC-K20-Proximity (from the manufacturer Shenzhen Yashi).

⚠️ Warning: When you change the plume or sensor, make sure to calibrate the sensor. To do this, in the engineering menu (#6484##), select Proximity Sensor Calibration and follow the instructions. Without calibration, the sensor may fire too early or, conversely, late.

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If the sensor doesn't work after you've been replaced, check the integrity of the tracks on the motherboard, and often, if you're not doing it carefully, the contact areas under the plume connector break off.

Alternative solutions: what to do if repair is not possible

If it is not feasible to replace the sensor or plume (for example, due to high cost), alternative methods can be used:

1.Switching off the sensor programmatically

In some firmware for the Mi 9T, you can turn off the proximity sensor so that the screen does not go out during calls.

1. Install the Xposed Framework (root required).
2. Activate the Disable Proximity Sensor.
3. Reboot the phone.

Cons: You will have to manually lock the screen during a conversation to avoid accidental taps.

2. Use of headphones

If the sensor doesn’t work but you need to call, use a wired headset with a microphone, in which case the screen won’t go out because the phone “understands” that you’re not pressing it against your ear.

Installation of custom firmware

Some custom firmware (like LineageOS or Pixel Experience) have more flexible proximity sensor settings.

• 📱 Set up the delay response.
• 🔄 Disable the sensor only for certain applications.
• 🛠️ Emulate its work through software.

However, keep in mind that installing custom firmware requires unlocking the bootloader and may deprive you of the warranty (if it is still valid).

4. Contact the service

If you're not sure about your skills, you should go to a service center.The average cost of replacing the plume with the sensor in the Mi 9T:

FAQ: Frequent questions about the proximity sensor in the Mi 9T