How to check the proximity sensor on Xiaomi Redmi Note 9S

Xiaomi Redmi Note 9S is a popular smartphone with excellent value for money, but even it is not immune to hardware problems. One of the frequent malfunctions is the malfunction of the proximity sensor, which is responsible for turning off the screen during a conversation. If the screen does not go out during a call, accidentally press buttons or, conversely, the screen does not turn on after the call is completed, this sensor is to blame.

In this article, you will learn how to check the proximity sensor on the Redmi Note 9S without visiting the service center. We will look at all the methods available, from built-in tests to using third-party applications, and also understand when the problem is software (and it can be fixed yourself) and when it is hardware (and needs repair).

Why you need a proximity sensor and how it works

The proximity sensor in the Redmi Note 9S is located next to the front camera and is an infrared sensor, whose main task is to detect when the phone is brought to the ear during a call, and when it is triggered, the sensor sends a signal to the system, and the screen goes out to:

• 📵 Prevent accidental tapping of the cheek or ear
• 🔋 Save battery power
• 🎧 Automatically switch to speaker when the phone is moving away from the ear

The principle is simple: the sensor emits infrared beams and analyzes the reflected signal. If the obstacle (for example, the ear) is too close, the sensor works. The Redmi Note 9S uses the STK3338 sensor (or its analogue), which is integrated into one module with the light sensor.

If the sensor fails, users face the following problems:

• 📱 The screen does not go out during the call.
• 🔄 The screen is not turned on after the call is complete.
• 🤯 Accidental taps during a conversation (call reset, hands-free switching on)
• 🔦 Automatic brightness control is not working correctly (light sensor is connected to the proximity sensor)

Signs of malfunction of the proximity sensor

Before you check the sensor, make sure it's the one that's the problem.

If you see any of these symptoms, the proximity sensor needs a diagnosis, but don't rush to take your phone apart, because 60 percent of the time, it's software-based.

⚠️ Warning: If the sensor stops working after a phone drop or moisture hits, there is a high probability of physical damage, in which case a self-check may not work, and a diagnosis will be required at the service center.

Method 1: Checking through the engineering menu (test codes)

The most reliable way to diagnose is to use a hidden engineering menu, which allows you to test the sensor in real time without third-party applications.

Instructions:

1. Open the Phone app.
2. Enter the combination: ##6484## (or #4636## → Equipment Testing).
3. Select Proximity Sensor (Proximity Sensor).
4. Cover the sensor with your hand or hold the phone to your ear.

Result:

• 🟢 0 (or Far) - the sensor is working, no obstructions.
• 🔴 1 (or Near) - The sensor is activated, an obstacle is detected.
• ❌ No response - the sensor is faulty.

If the values do not change when covering the sensor, the problem may be:

• 🧹 Sensor contamination (dust, fat, protective film)
• 🔧 Damage to the plume or the sensor itself
• 🖥️ Firmware failure (solved by resetting or flashing)

Make sure there is no protective film on the sensor | Clear the sensor area of dust and dirt |Close all background applications |Check that the battery is at least 20%-->

Method 2: Diagnostics through applications (without root)

If the engineering menu is not available or does not show data, use third-party utilities.

• 📱 Phone Doctor Plus – shows the sensor status in real time and tests other sensors.
• 🔍 Sensor Box for Android – displays the sensor’s schedule (useful for “watering” analysis).
• 🛠️ CPU-Z — In the Sensors section, the proximity sensor data (if supported) is displayed.

How to check with Sensor Box:

1. Install the app from Google Play.
2. Open the Proximity tab.
3. Watch the chart: when the sensor is covered, the line should rise sharply (or change color).

If the schedule does not respond to obstacles, the problem may be:

• 🔌 Disabled sensor at OS level (check call settings).
• 🛠️ Damaged plume (disassembly required).
• 📱 Failure in the firmware (will help reset to factory settings).

⚠️ Warning: Some apps (e.g., AIDA64) may not show proximity sensor data on Xiaomi due to limitations MIUI In this case, use Phone Doctor Plus – it works stably.

💡

If the sensor is running with a delay (1-2 seconds), try calibrating it through the engineering menu (#6484## → Calibrate Proximity Sensor).

Method 3: Visual inspection of the sensor

Sometimes the problem isn't with the sensor itself, but with the physical lock. Look at the top of the Redmi Note 9S screen (near the front camera):

• 🔍 Check if the sensor is covered with a protective film or glass (especially if a new one has been recently glued).
• 🧴 Make sure there is no layer of dirt, grease or glue residue on the sensor.
• 💡 Light up with a flashlight: the sensor should look like a small black hole (sometimes with a white dot).

If the sensor is blocked, clean it carefully:

1. Use a soft brush or compressed air (a canister for cleaning equipment).
2. Wipe the sensor area with an alcohol tampon (do not pour liquid directly onto the phone!).
3. If the problem is in the film, gently tuck it with a plastic card and remove the extra layer.

On the Redmi Note 9S, the proximity sensor often stops working after changing the glass or display. If you have recently repaired the screen, check if the new module is installed correctly and if the sensor plume is damaged.

Method 4: Verification through call settings

Sometimes the sensor is functional, but it's locked at the setting level. There are hidden parameters in MIUI that can affect the sensor.

How to check:

1. Open Settings → Applications → Application Management.
2. Find the Phone app and open its settings.
3. Select Permissions and make sure the application has access to Sensors.
4. Return to Settings → System settings → Additional → Special features.
5. Check if the Autoturn option is disabled during the call (sometimes conflicts with the sensor).

If the settings don’t help, try resetting your network settings:

1. Go to Settings. → SIM-maps and mobile networks.
2. Select Network Resetting.
3. Confirm the action and restart the phone.

⚠️ Warning: Once the network is reset, you have to re-enter Wi-Fi passwords and adjust mobile internet settings, which helps if the problem is caused by a failure in the communication module.

Method 5: Hardware verification (for experienced users)

If software methods didn't work, the problem might be physical damage to the sensor or its plume, and the diagnosis would require a partial disassembly of the phone.

What to check:

• 🔌 The sensor plume -- it goes from the top of the display to the motherboard, often departs after falls.
• 🛠️ The sensor itself — check it for cracks or oxidation of the contacts.
• 🔋 Contacts on the board - sometimes oxidized or soldered off.

To disassemble the Redmi Note 9S, you will need:

• 🔧 Plastic mediators (to remove the back cover).
• ⚡ Screwdriver T3 and T5 (for screws).
• 🧲 Screen removal suction cup (optional).

If you're not sure about your skills, don't take your phone apart on your own, call the service. Damage to the plume of the display or motherboard can result in expensive repairs.

💡

If the proximity sensor does not work after the display is replaced, 90% of the time the problem is with the wrong plume or damaged sensor on the new module.

What to do if the sensor is faulty

If the diagnosis confirmed a sensor malfunction, you have several options:

If you want to repair your phone yourself, consider:

• 🔧 The Redmi Note approximation sensor 9S often comes in the same module as the light sensor, and you'll have to change both when you replace it.
• 📦 Parts are best bought in trusted stores (e.g. AliExpress with a seller rating above 98%).
• 🔋 After the sensor is replaced, calibration may be required through the engineering menu.

FAQ: Frequent questions about the proximity sensor