Approximation Sensor on Xiaomi Redmi 9T: how to adjust, check and fix

The proximity sensor in the Xiaomi Redmi 9T is a small but critical element that is responsible for turning off the screen during a phone conversation. When you hold your smartphone to your ear, the sensor detects the obstacle and extinguishes the backlight, preventing accidental pressing and saving battery power. However, over time, this module can start to malfunction: the screen does not go out when you call, react with a delay or, on the contrary, it turns off for no reason. In 80% of cases, the problem can be solved independently without going to the service center.

In this article, we will explore all the possible ways to adjust the proximity sensor on the Redmi 9T, from software calibration through the engineering menu to hardware methods (cleaning, replacing), you will also learn how to check the performance of the sensor with hidden tests and what to do if standard methods do not help, and pay special attention to the typical user errors that often exacerbate the problem.

If your Redmi 9T stopped extinguishing the screen during calls, do not rush to blame the firmware or MIUI "glitches." In most cases, it is the proximity sensor that is to blame - either its software setting is lost or the sensor is physically contaminated. The first thing to do is to eliminate software failures.

How does the proximity sensor in Xiaomi Redmi 9T

The approach sensor in Redmi 9T is an infrared sensor located at the top of the screen (near the front camera), which consists of two elements: an emitter (sends an IR signal) and a receiver (reflects the signal). When you bring the phone to your ear, the infrared beam reflects from the surface and returns back, the sensor recognizes this as an obstacle and sends a command to turn off the screen.

At Redmi. 9T model sensor STK3311 (Or similar), which is integrated into a common module with a light sensor, and its operation is controlled by the firmware through the driver. proximity_sensor.ko. It is important to understand that failures can be caused by hardware problems (pollution, damage) and software problems (incorrect settings, errors). MIUI).

The default sensor response distance is 3-5 cm If the screen goes out too early or, conversely, does not respond to the approach, this is a signal that calibration is necessary. In rare cases, the problem lies in the incompatibility of the firmware with the version of the sensor driver (relevant for custom ROM).

To understand whether the sensor is to blame for the incorrect operation of the screen, conduct a simple test:

• 📞 Call another phone and bring Redmi. 9T ear-to-ear.
• 👁️‍🗨️ Check if the screen is late or late.
• 🖐️ Try to cover the top of the screen with your palm (without touching the sensor!) – the reaction should be instantaneous.

Checking the proximity sensor through the engineering menu

Before you start adjusting, you need to make sure that the sensor works at all. For this, the Xiaomi Redmi 9T has a hidden engineering menu where you can test all the sensors.

1. Open the Phone app.
2. Enter the combination: ##6484## (or #4636## → "Equipment Testing").
3. Select Proximity Sensor (Proximity Sensor).
4. Cover the top of the screen with your hand – the value should change from 5.00 cm to 0.00 cm.

If the values do not change or if the Failed error is displayed, this may mean:

• 🔧 Software failure – calibration or resetting of settings is required.
• 🧹 Sensor contamination – dust or fat blocks the IR signal.
• 🔨 Hardware malfunction - the module itself or the plume is damaged.

The engineering menu also shows the current value of the trigger threshold (usually 3-5 cm) if it is very different from the norm, you will need to manually adjust it.

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If the engineering menu doesn’t open, check to see if hidden features are disabled in the developer settings. Go to Settings → About Phone → MIUI version and tap 7 times on the line to activate the developer mode.

Calibration of the proximity sensor without root rights

If the sensor is responsive to the approach, but is unstable (for example, the screen goes out with a delay), software calibration will help. In Redmi 9T, it is performed through standard MIUI settings:

1. Go to Settings → About the phone → All specs.
2. Tap 5 times on the kernel line (or MIUI version) to open the test menu.
3. Choose a Single Item Test → Proximity Sensor.
4. Follow the instructions on the screen: the system will suggest covering the sensor and removing the hand to automatically adjust the trigger threshold.

If this method didn’t work, try an alternative method through the Developer Settings:

1. Activate the Developer Mode (as described above).
2. Go to Settings → Additional → For developers.
3. Find the Debugging Approach Sensor (or Proximity Sensor Calibration) option and turn it on.
4. Reboot the phone.

After calibration, check the sensor with a call, if the problem persists, you may need to reset the sensors to the factory.

1. Go to Settings → System → Resetting settings.
2. Select Reset Sensor Settings (not to be confused with a full reset!).
3. Confirm the action and wait for the reboot.

Make sure there is no protective film or glass on the screen.|Clean the top of the screen from dust and fat|Close all background applications|Connect your phone to charge (the battery must be at least 50 times charged%)-->

Manual adjustment of the trigger threshold (for experienced users)

In some cases, automatic calibration fails, and you need to manually adjust the trigger threshold, which requires access to the file system (without root rights, this method will not work). If you have root, follow these steps:

1. Install a file manager with root support (e.g., Root Explorer or Solid Explorer).

2.Cross the path:

/sys/class/sensors/proximity/proximity_threshold

3. Open the file. proximity_threshold and change the meaning:

• 📱 For Redmi. 9T optimal range – 3-7 (where 3 is the minimum response distance, 7 is the maximum response distance).
• 🔧 If the screen goes out too early, increase the value (for example, from 3 to 5).
• 🔍 If the sensor does not respond, reduce the value (for example, from 7 to 4).

4. Save the changes and restart the phone.

If root-rights are not available, you can try to change the threshold through ADB-commands (without unlocking the bootloader):

adb shell


su




echo 5 > /sys/class/sensors/proximity/proximity_threshold

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Attention: Incorrect values in proximity_threshold If the screen stops going out after the changes, return the standard value (3) or reset the settings.

Cleaning and hardware repair of the sensor

If the software didn't work, the problem is probably physical contamination or damage to the sensor. In the Redmi 9T, the proximity sensor is located under the top glass of the display, and over time it accumulates dust, fat or glue residue from the protective film, to clean the sensor:

1. Turn off the phone and remove it. SIM-map.
2. Carefully tuck the top of the screen with a plastic spatula (do not use metal!).
3. Blow dust off the sensor area with compressed air or wipe with a cotton swab soaked in isopropyl alcohol.
4. Make sure there are no scratches or chips on the sensor – if there are any, the sensor should be replaced.

If the sensor does not work after cleaning, check:

• 🔌 The display plume - it could move away during disassembly.
• 🛠️ Integrity of contacts on the board (oxidation, breaks).
• 🔋 Power module - measure the voltage on the sensor contacts with a multimeter (should be ~3.3V).

Replacing the proximity sensor with the Redmi 9T will cost 500-1500 rubles (depending on the service), self-replacement is possible, but requires experience with soldering equipment, since the module is soldered to the motherboard.

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If the proximity sensor stopped working after the phone fell or moisture hit, there's a 90% chance it'll need to be replaced. Software methods won't help here.

Additional ways to resolve the problem

If the standard methods didn’t work, try these alternative solutions:

Disconnection of energy saving mode:

In some versions of MIUI, battery saving blocks sensors. Go to Settings → Battery → Power Saving Mode and turn it off.

Firmware update:

Sensor failures are often fixed in newer versions of MIUI. Check for updates in Settings → About Phone → System Update.

3. Use of third-party applications:

Apps like Proximity Sensor Reset or Sensor Test can help reset the sensor, but beware — some utilities require root rights.

4. Reset to factory settings:

If the problem occurs after installing applications or changing system files, perform a full reset (don’t forget to back up the data!).

Verification for viruses:

Some malware blocks the sensors. Scan your phone with an antivirus (e.g. Malwarebytes).

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Attention: If after all the manipulations, the proximity sensor has not worked, do not try to disassemble the phone without experience. In the Redmi 9T, the display module is glued to the frame, and careless disassembly can lead to damage to the plume or matrix, in which case it is better to contact the service center.

Frequent errors in adjusting the sensor

Many users make the proximity sensor problem worse by making typical errors.

1. Use metal objects for cleaning:

Even a soft screwdriver can scratch the sensor or damage the plume.

2. Install unofficial firmware without compatibility check:

Some custom ROMs do not support Redmi 9T sensor drivers.

3. Ignore MIUI updates:

Xiaomi regularly releases patches to fix sensor bugs.

Independently solder the sensor without experience:

The wrong ration can disable the motherboard.

Adjust the threshold of operation "by eye":

Always follow the recommended values (3-7 for Redmi 9T).

If you made one of these errors, return the phone to its original state (resetting, flashing) and repeat adjusting the sensor from scratch.

FAQ: Answers to Frequent Questions