How to set up the proximity sensor on Xiaomi Redmi Note 9 Pro: the full guide

The Xiaomi Redmi Note 9 Pro is one of the most popular mid-range smartphones, but even it has problems with its proximity sensor. This small but important sensor is responsible for turning off the screen during a phone call when you hold the device to your ear. If the sensor is not working properly, the screen may go out too early, not switch off at all or behave unpredictably. In this article, we will discuss how to check, configure and calibrate the proximity sensor on the Redmi Note 9 Pro without going to the service center.

Sensor problems often occur after MIUI updates, mechanical damage (such as a phone crash) or because of sensor contamination, and in 90% of cases, they can be fixed by software, either through system settings or engineering menus. We will look at all available methods, including hidden MIUI functions that are not documented in the official instructions.

What is a proximity sensor and how does it work

The proximity sensor in the Redmi Note 9 Pro is an infrared sensor that detects the distance between the screen and an object (like your ear).

• 🔦 Infrared emitter emits invisible light.
• 📡 Photodiode – captures the reflected signal and transmits data to the processor.

When you hold your phone to your ear while you're ringing, the sensor picks up the obstacle and tells the system to turn off the screen and touch buttons. This prevents accidental taps and saves battery life. The Redmi Note 9 Pro uses a model sensor, STK3338 (or similar), which is integrated into the top of the display next to the front camera.

The sensor can operate at a distance of up to 5-7 cm, which is enough for comfortable use, but over time, its sensitivity may decrease due to:

• 🧹 Pollution (dust, greasy stains on glass).
• 🔧 Software failures (errors in firmware) MIUI).
• 💥 Mechanical damage (cracks on glass, impacts).

How to check the operation of the proximity sensor

Before you set up the sensor, make sure it's really the problem.

1. Open the phone app and dial the combination: ##6484##
2. The Manual Test Mode menu will appear on the screen.
3. Select Proximity Sensor (approximation sensor).
4. Hold your hand or a piece of paper to the top of the screen (where the front camera is located).

If the sensor is in good shape, the screen will show the words Near (close) or the number 0 (usually indicating that the object is detected). When you remove the hand, the value should change to Far (far) or 1. If there is no reaction or values do not change, the sensor is defective or contaminated.

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If the test mode does not open, try entering the combination ##4636## and select Usage statistics. → Sensor test. On some versions MIUI This path works more stable.

You can also use third-party applications for diagnosis, for example:

• 📱 Phone Doctor Plus (checks all sensors).
• 🔍 Sensor Box for Android (Shows Values in Real Time).
• 🛠️ CPU-Z (sensors).

⚠️ Warning: If the sensor doesn't respond even in test mode, the problem may be hardware, in which case only replacing the sensor or the entire display module will help (on the Redmi Note 9 Pro, the sensor is soldered to the screen plume).

Adjust the proximity sensor through standard MIUI settings

In most cases, sensor problems are solved through standard MIUI settings.

1. Open the Settings. → System system → Additionally.
2. Select Special Opportunities.
3. Scroll down and find the System Settings section.
4. Activate the option to automatically turn off the screen during the call (if it is disabled).

If the option is already on, but the sensor is not working correctly, try turning it off and turning it on again.

• Open the phone. → ⋮ (menu) → Settings.
• Select Calls → Additional settings.
• Make sure that the approach sensor option is enabled.

"Automatic Screen Shutdown" option in special features enabled |

The proximity sensor is activated in the settings of the "Phone" application |

Test mode shows correct values (0/1 or Near/Far)|

There is no protective film or glass on the screen that blocks the IR signal.-->

If after these manipulations the sensor still does not work, proceed to calibration through the engineering menu.

Calibration of the proximity sensor through the engineering menu

The Engineering Mode is a hidden settings section that allows you to manually calibrate sensors, and on the Redmi Note 9 Pro, it is accessed through a secret code:

1. Open the Phone app.
2. Enter the combination: ##36446337##
3. The Engineering Mode menu (can be called MTK Engineer Mode or Qualcomm Engineer Mode depending on the processor) will appear on the screen.

Then proceed according to the version of the firmware:

After calibration, restart your phone. If the sensor still doesn't work, try resetting to factory settings (but back up the data first!).

⚠️ Warning: Do not change other options in the engineering menu unless you know their purpose. Incorrect settings can cause failures in the communication module or camera.

Software Solutions: Resetting and Updating the Firmware

If the hardware calibration didn't work, the problem could be the software.

• 🔄 Resetting settings: Go to Settings → The phone. → Reset settings and select Reset all settings. This will delete user data, but save files to internal memory.
• 📲 Update MIUI: Go to Settings. → The phone. → Update the system and check for new firmware versions. Often sensor bugs are patched.
• 🛠️ Install custom firmware: If the problem persists on the official firmware, try going to Xiaomi.EU or LineageOS. 4PDA or XDA Developers.

On the Redmi Note 9 Pro with MIUI 12.5 firmware and later, the proximity sensor can conflict with the Raise to Wake function. Turn it off in Settings → Screen → Raise to wake up if the screen goes out arbitrarily.

If the sensor stops working after the upgrade, reset to factory settings, and sometimes newer versions of MIUI reset the sensors.

Hardware problems: cleaning and replacing the sensor

If the software didn't work, it could be because of physical damage to the sensor, and here's what you can do yourself:

• 🧼 Sensor cleaning: Gently wipe the top of the screen (near the front camera) with a cotton swab dipped in alcohol!
• 🔧 Security glass check: Thick or poor quality glass can block the IR signal. Try temporarily removing it and testing the sensor.
• 🔨 Diagnostics of the plume: If the phone fell, the sensor plume could have moved away. To check, you will need to disassemble the device (we recommend contacting the service).

The cost of replacing the proximity sensor on the Redmi Note 9 Pro in service centers is 800-1500 rubles (depending on the region).

• The sensor is soldered to the flexible plume of the display, so replacing requires soldering work.
• With careless disassembly, you can damage the camera plume or microphone.
• After replacement, recalibration through the engineering menu may be required.

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If the sensor is physically damaged and the phone is warranty--don't disassemble it yourself! - Contact the Xiaomi Authorized Service Center, or the warranty will be canceled.

Frequent Mistakes and How to Avoid Them

When setting up the proximity sensor, users often make mistakes that exacerbate the problem, and here are the most common ones:

Another common mistake is using magnets or metal inserts, which can interfere with the IR sensor, and if you notice that the sensor starts to malfunction after you buy a new case, try temporarily removing it and testing the sensor.

FAQ: Answers to Frequent Questions