The proximity sensor in Xiaomi Redmi 9 with NFC is a small but critical element that automatically shuts down the screen during phone calls. When you bring the device to your ear, the sensor registers the obstacle and extinguishes the backlight, preventing accidental pressing and saving battery power. However, many users face problems: the screen does not turn off when calling, the sensor is delayed or works unstable, most often due to improper settings, sensor contamination or software failures.
In this article, we will discuss how to test the sensor, calibrate it through the engineering menu, adjust sensitivity and fix typical problems. We will focus on the nuances of the Redmi 9 model with NFC, since its hardware platform has specific features compared to other devices in the line, you will also learn how to reset the sensor to factory settings and what to do if the problem lies at the firmware level.
Where is the proximity sensor in Xiaomi Redmi 9 and how it works
In Redmi 9 (including the NFC version), the proximity sensor is located at the top of the screen, next to the speaker for conversations. It's an infrared sensor that emits invisible light and analyzes the reflected signal. When you hold the phone to your ear or other object, the sensor detects the change in reflected radiation and sends a command to the system to turn off the screen.
It is important to understand that the operation of the sensor depends on several factors:
- 🔹 Surface cleanliness: Fat, dust, or protective film may block the signal.
- 🔹 Software calibration: factory settings may be lost after updates MIUI.
- 🔹 Hardware damage: Falls or moisture often disable the sensor.
- 🔹 Version of firmware: in old builds MIUI There were bugs with the sensor signal processing.
The Redmi 9 uses a model sensor, STK3311 (or similar), which is integrated into a single module with light, which means that if the automatic brightness sensor stops working, there is a high probability of problems with the proximity sensor.
How to check the operability of the sensor of approach
Before you set up the sensor, make sure it's functioning at all. There are several ways to do this:
- Test using USSD code: dial in the phone keyboard ##6484## (or #4636## → Testing → Sensors). In the list, find Proximity sensor – covering the top of the phone with your hand, the value should change from 5.00 (no obstacle) to 0.00 (object detected).
- Manual test: Call your phone (or use the Dictator app to simulate a call) and cover the top with your palm. The screen should go out in 1-2 seconds.
- Third-party apps: Install Sensor Test or CPU-Z from Google Play, which displays real-time data from all sensors.
If the sensor does not respond to any of the tests, the problem may be:
- 🛠️ Sensor contamination (wipe the top frame with an alcohol napkin).
- 📱 Firmware failure (try restarting your phone).
- 🔧 Damage to the plume (diagnosis is required at the service center).
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If the sensor only works at a certain angle, it is likely that its calibration is disturbed, and this is corrected through the engineering menu (see the next section).
Calibration of the proximity sensor through the engineering menu
If the sensor is working but not correctly (e.g., the screen is dimming with a delay or not turning back on), calibration will be required. On Xiaomi Redmi 9, this is done via the hidden engineering menu of MTK Engineer Mode (for MediaTek processors) or Qualcomm Service Menu (for Snapdragon). Your model uses a MediaTek Helio G80 chipset, so the instruction will be for the MTK.
Step-by-step:
Open the phone app and enter ##36446337##
Go to Hardware Testing → Sensor → Proximity Sensor
Click "Do Calibration" and follow the prompts on the screen
After calibration, restart the phone
Check the sensor during the test call-->
If there is no calibration item on the menu, try an alternative method:
- Install the MTK Engineering Mode app from Google Play.
- Open it and go to Hardware Testing → Sensor → Proximity Sensor.
- Write down the current Min and Max values (usually 0 and 5).
- Press Calibrate and wait for the process to be completed.
Once calibrated, the sensor should fire faster, and if the problem persists, it may need to reset the sensor settings (more on this in the next section).
What to do if the engineering menu is not opened?
Reset sensor settings to factory parameters
If the calibration doesn’t work, the next step is to reset the sensor settings, which will return all the parameters of the proximity sensor (and other sensors) to the original values. On the Xiaomi Redmi 9 with NFC, the reset is only performed through a full reset of the phone settings or using ADB.
Method 1: Through phone settings (soft reset)
- Go to Settings → About the phone → Reset settings.
- Select Reset Application Settings (does not delete data, but resets system settings).
- After restarting, check the sensor.
Method 2: ADB (for experienced users)
Connect your phone to your PC, turn on USB Debugging and execute the command:
adb shell pm clear com.android.providers.settingsThis command will reset the settings of all sensors, including the proximity sensor.
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Resetting sensor settings does not delete your data (photos, contacts), but may require re-tuning screen brightness, gestures, and other settings.
Adjustment of the proximity sensor sensitivity
Some MIUI firmware has hidden parameters to adjust sensor sensitivity, which is useful if the sensor is triggered too early (the screen goes out at the slightest approach of the hand) or, conversely, reacts late.
How to change the threshold of response:
- Install the BuildProp Editor app (root rights required!).
- Find ro.proximity.delay (delay) and ro.proximity.threshold (sensitivity threshold).
- For Redmi 9, optimal values are: ro.proximity.delay=100 (delay in MS) ro.proximity.threshold=3 (threshold where 0 is maximum sensitivity)
Save the changes and restart the phone.
Without root rights, you can not change these parameters, but you can try an alternative way:
- 📱 Install the Sensor Disabler app (disables the sensor completely if it interferes with the sensor).
- 🔧 Use Magisk modules for fine tuning (e.g. Proximity Sensor Fix).
| Parameter | Default value | Recommended value | The effect |
|---|---|---|---|
| ro.proximity.delay | 200 | 100–150 | Reduces screen shutdown delay |
| ro.proximity.threshold | 5 | 2–4 | Increases sensitivity to obstacles |
| persist.sys.proximity_offset | 0 | 1 | Corrects the shift of the sensor |
Frequent problems and their solutions
Even after setting up, the proximity sensor on Redmi 9 may not work properly.
⚠️ Warning: If the sensor stops working after a phone drops or moisture hits, don't try to calibrate it software.This is a hardware malfunction that requires a replacement of the sensor or plume.
Problem 1: The screen does not go out during the call
- 🔍 Check if the sensor is blocking the protective glass or cover.
- 📱 Update the firmware to the latest version MIUI (In older versions, there were bugs with signal processing).
- 🔧 Calibrate through the engineering menu (see section above).
Problem 2: The sensor is going off too late.
- 🛠️ Reduce the value of ro.proximity.delay (root required).
- 📊 Check if your phone is overloaded (close the background apps).
- 🔄 Reset sensor settings through ADB.
Problem 3: The screen does not turn on after the call is completed
- 🔋 Check if the battery is discharged (at low charge, the sensor can glitch).
- 📱 Turn off the "Energy Saving" function in the settings.
- 🔧 Reinstall the firmware via Fastboot (if the problem has appeared after the update).
⚠️ Warning: If the sensor doesn't work after all the manipulations, check it through the test menu (##6484##).If the values don't change when you close the sensor, it's a 100% hardware malfunction.
Alternative ways to control the screen during a call
If the proximity sensor is not repairable, workaround solutions can be used:
- 📱 Substitute applications: Proximity Sensor Fix (simulates the sensor operation) Gravity Screen (disables the screen by movement).
- 🔧 Settings MIUI: Turn on the option to turn off the screen when you lift to the ear in Settings → Special facilities → Universal access. Use the "Raise to wake up" gesture to quickly turn on the screen after the call.
- 🛠️ Hardware solutions: Replace the sensor module (repair cost) ~1500–2500 ₽). Use headphones with a microphone to make calls.
The downside of alternative methods is increased battery consumption (constant operation of the accelerometer) or less convenient control, and the best option is to repair the sensor if the phone is still warranty.