Why the Redmi 9C NFC's proximity sensor may not work - and how to fix it
The proximity sensor on the Xiaomi Redmi 9C NFC is a small but critical element that automatically shuts down the screen during a phone conversation. If it is inactive or incorrectly configured, you risk accidentally pressing buttons with your cheek, interrupting calls or wasting battery power on the display. In this article, we will examine where the sensor settings are hidden, how to force it to activate (including hidden MIUI options), and what to do if the sensor ignores your touch.
Feature of the Redmi model 9C NFC (The code name angelicanfc is that the manufacturer often hides advanced sensor settings under the "engineered menu" or disables them in standard firmware. We will show legal ways to access these parameters without risking damage to the system - from basic actions in the interface. MIUI prior to code use USSD and ADB-Teams (for advanced users).
Where is the proximity sensor on the Redmi 9C NFC physically located?
Before you set up the software, it's useful to know where the sensor is. On the Redmi 9C NFC, the proximity sensor is integrated into the top of the display, to the right of the front camera (when you look at the screen), it's an infrared sensor that responds to obstacles at a distance of 0.5-3 cm. Its work is based on infrared reflection: when you hold the phone to the ear, the sensor detects the proximity of the object and sends a signal to the system to turn off the backlight.
On the outside, the sensor looks like a tiny black hole (sometimes a gridded speaker). On some Redmi 9C NFCs, it can be almost invisible, especially if the phone's body is dark. To accurately identify its location, light it up at an angle, the sensor will reflect light poorly.
- 🔍 How to check physical fitness: gently wipe the top of the screen with an alcohol wipe. Dust or greasy prints can block the IR ray.
- ⚡ Signs of malfunction: the screen does not go out during the call, even if you press the phone tightly to the ear, or vice versa – goes out arbitrarily during normal use.
- 🛠️ What not to do: Trying to clean the sensor with a needle or toothpick will damage the sensitive element.
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If the sensor still does not respond after cleaning, try to remove the protective film or cover - they can block the IR signal.
Standard way to enable proximity sensor through MIUI settings
In most cases, activating the sensor doesn't require any additional manipulations, it's on by default, but after resetting the settings, updating the firmware or installing custom software, the settings may go wrong, to return them to working condition:
- Open the Settings app (the gear icon on the home screen).
- Go to the System and Device section → Additional settings.
- Select the Special Opportunities item.
- Scroll down to the Physical buttons and gestures block and tap on Automatic Screen Shutdown.
- Make sure that the slider is in the position on (green).
If this item is not in your MIUI version (e.g., in firmware for the global market), try an alternative way:
Settings → Applications → Application Management → Three dots (menu) → Special access → Disconnect the screen during a callCall another phone and bring Redmi. 9C NFC ear-to-ear|The screen should go out in 1-2 seconds.|Take the phone away - the lights should turn back on|Repeat the test 2-3 times for reliability-->
Hidden sensor settings: engineering menu and USSD-code
When standard methods fail, service menus come to the rescue, allowing you to test hardware components directly, bypassing the limitations of MIUI. Two things are relevant for the Redmi 9C NFC:
Method 1: USSD-sensor-code
In the application Phone combination:
##6484##Once you enter, the Manual Test menu will open. Select Proximity Sensor. When you put your hand on top of the screen, the value should change from 5 (no obstacle) to 0 (object detected). If the numbers do not change, the sensor is faulty or disabled at the firmware level.
Method 2: MTK Engineering Menu
The Redmi 9C NFC is built on the MediaTek Helio G35 chipset, so there's an extended engineering menu available for it.
- Call on your phone: ##36446337##.
- Go to Hardware Testing → Sensors → Proximity Sensor.
- Press the Start Test and watch the chart. The green line should drop sharply when you approach your hand.
What to do if the engineering menu is not opened?
Proximity Sensor Problems on Redmi 9C NFC and Their Solutions
Even when properly configured, the sensor can malfunction, and let's look at typical scenarios and how to fix them:
| Problem. | Possible cause | Decision |
|---|---|---|
| The screen does not go out during the call. | Sensor contaminated or covered with a cover | Clean the top frame of the screen, remove the case |
| The screen goes out arbitrarily | Sensitivity of the sensor is overstated | Calibrate the sensor through the engineering menu |
| The sensor is not responding at all. | Software failure or damage to the plume | Reset the settings to the factory or contact the service |
| It only works after the reboot. | Conflict with MIUI optimization | Turn off RAM autocleaning in battery settings |
A critical feature of the Redmi 9C NFC: on some batches of devices, the proximity sensor is physically absent, despite the indications in the specifications. This is due to the optimization of production costs. You can only check the presence of the sensor through the engineering menu - if the Proximity Sensor item is not there, then your model is equipped with software emulation (the screen goes out by the timer, not by the sensor signal).
Calibration of the proximity sensor: when and how to do it
If the sensor is not responding in a stable way (e.g., it is delayed or falsely triggered), it needs to be calibrated. MIUI does not have a built-in tool for this, but you can use third-party utilities or engineering menus.
Method 1: Sensor Calibration App
Download the app from the Play Market, launch it, and select Proximity Sensor. Follow the on-screen instructions – you usually need to bring and move your hand from the sensor 3-5 times to determine thresholds.
Method 2: Manual calibration via ADB
For advanced users who are ready to work with the command line:
- Connect your phone to your PC and enable USB Debugging in the developer settings.
- Enter the command: adb shell settings put system proximity_delay 1000 (where 1000 — delay time in milliseconds; default is usually 500).
- Reset the device.
⚠️ Attention: Inept work with ADB If you are not sure about your actions, use only the first method (via the application).
What to do if nothing helps: radical measures
If the proximity sensor on the Redmi 9C NFC stubbornly refuses to work despite all attempts, there are three options left:
- 🔄 Reset to factory settings. Before you do, back up your data through Settings. → Additionally. → Backup.
- 📥 Download the official firmware for your model from Xiaomi and follow the installation instructions via the Mi Flash Tool.
- 🔧 If the sensor is physically damaged (for example, after a phone crash), it will cost 800-1500 rubles to replace it depending on the region.
Before you carry your phone for repair, check if the failure is related to the MIUI update. For example, MIUI 12.5.3 and 12.5.4 for the Redmi 9C NFC, there was a bug that caused the proximity sensor to shut down after installing security patches, solved by rolling back on a previous build or waiting for a new update.
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Before resetting or flashing, check if the app you installed is blocking the sensor (such as call or screen managers), run the phone in safe mode (hold the power button → Safe Mode) and repeat the test.