Buying a smartphone, especially from hand or in questionable stores, is always risky. You may encounter a restored device, fake or gadget with hidden defects. Owners of Xiaomi, Redmi and Poco devices have the unique advantage of a built-in powerful diagnostic tool, available without installing third-party programs. This feature is embedded in the shell of MIUI and allows you to conduct a deep check of all nodes of the device.
Before you go to complex tests, you need to perform basic visual and software inspection. Pay attention to the build quality: the gaps between the case and the screen should not be too large, and the buttons should have a clear stroke. IMEI-This is a unique device identifier that must match the box, system settings, and special engineering menu, and the mismatch of this data is the first sign that the phone may have been repaired or assembled from different parts.
Next, we'll look at how to run a hidden engineering menu and interpret test results. The engineering menu is not just a feature list, it's direct access to hardware-level diagnostic tools. Using these tools will help you avoid buying defective goods or detecting a problem while the warranty is in place. Don't ignore this stage, because some defects can only manifest under load or in specific modes of operation.
⚠️ Warning: Before starting a deep diagnostic, make sure to back up important data. Although the tests are safe, accidental resetting of settings in the engineering menu can lead to loss of information.
Starting an engineering menu through a secret code
The fastest and most reliable way to get into the testing mode is the use of a special test. USSD-It works on most models, from the budget Redmi to the flagship Xiaomi 13 and 14 series. You don't need root rights or a computer connection to activate. Just open the standard Phone program and type in the character combination.
The entry code is as follows:
##6484##After entering the last star, the menu should open automatically. If this does not happen, try an alternative ##4636##, which opens the phone information menu, or ##37378##. On some global versions of firmware, access to the full CIT-The menu (Customer Integration Test) can be limited, in which case you can try to enter through the settings: go to Settings → The phone. → The kernel version and quickly click on this line 5-7 successively.
The menu interface is a list of tests sorted by component. Here you will find checks for display, sensor, microphone, speakers, vibration, cameras, proximity and light sensors, and communication modules. Each item, when pressed, triggers a corresponding validation script. It is important to understand that some tests may require your active participation, such as pressing a screen or pronouncing words into a microphone.
What if the code doesn't work?
Diagnostics of the display and touch screen
The screen is one of the most expensive and vulnerable components of a smartphone. When checking a Xiaomi phone for sensor and matrix defects, you need to be especially careful. In the engineering menu, select the Display or Screen test. You will see a pure color image. Your task is to carefully examine the surface for broken pixels that may glow white, black or unnatural.
After checking the static image, the test will suggest changing the background color. Walk through the entire palette: red, green, blue, white and black. On the black background, you can see the lights (uneven illumination), and on the white one, you can see yellow spots or clouds. Pay special attention to the edges of the screen, where artifacts often appear after falls or poor-quality assembly.
The next step is to test the multi-touch, and in Touch or TouchPanel mode, the screen will ask you to swipe your finger along special lines or touch all the squares of the grid, and this is a critical test for detecting the sensor's dead zones, swipe your finger quickly and slowly, with a single touch and multiple fingers at the same time, and if the lines are interrupted or the squares don't light up in certain places, the sensor is faulty.
☑️ Screen checklist
Often users are faced with the problem of “phantom presses” when the phone itself reacts to touch. This can be a sign of poor-quality touchscreen or problems with the power controller. It is also worth checking the automatic brightness adjustment by closing the light sensor with your hand. If the brightness does not change smoothly or jumps, the sensor may be contaminated or defective.
Checking cameras, microphone and speakers
Multimedia capabilities are key for many users. In the CIT menu, select Camera. The test will run all the camera modules sequentially: wide-angle, TV, macro and front-facing. Pay attention to the speed of focus and the presence of foreign spots on images. Dust inside the camera module is a frequent sign of leaky body or poor build in the factory.
To test the sound, select the Speaker and Microphone test. In speaker mode, the phone will play the melody. Estimate the volume and purity of the sound: there should be no wheezing, cracking, or distortion at maximum volume. Then the system will ask you to record the sound through the microphone and play it back. Speak clearly, checking both the main and secondary microphones (usually two or three for noise reduction).
In the Vibrator test, the phone must vibrate at a certain frequency, and if the vibration is weak, intermittent, or accompanied by rattling of the body, this may indicate wear and tear of the motor or its poor attachment to the frame.
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When testing the cameras, point the lens at a light source (lamp) to check for “glare” or iridescent halos that indicate poor quality of the lenses or protective glass.
Don't forget to check the headphone jack (if you have one) and Bluetooth. The engineering menu often has a "Headset" test that determines the headset's connection. For Bluetooth, you can start a device search to make sure the module sees neighboring gadgets.
Testing of sensors and communication modules
A smartphone today is a set of sensors, and a failure in one of them can make it uncomfortable to use the device. In the Sensor or Proximity section, the proximity sensor is checked. Hold your hand to the top of the screen (above the speaker) - the screen should go out, remove it - light up. The faulty sensor causes the screen to stay on the screen during a conversation, and you cheek-drop calls.
The accelerometer and gyroscope are usually checked by tilting the phone in different directions, showing the movement of the virtual ball or changes in the digital metrics, if the reaction is delayed or the ball flies away without tilting, the calibration of the sensors is disrupted, and this also affects the operation of the autorotation of the screen and navigation applications.
The most important aspect is the operation of communication modules. SIM, WiFi and GPS tests make sure that antennas are in good working order. In GPS mode, the phone must quickly determine coordinates (with the Internet on for A-GPS). If the search for satellites takes minutes or coordinates "flew" into the ocean, with an antenna problem. WiFi check should show the list of available networks; if the list is empty, although the router is nearby, the WiFi module is defective.
| Component | What we check. | Sign of malfunction |
|---|---|---|
| Approximation sensor | Reaction to the approach of the object | The screen doesn't go out when you ring. |
| accelerometer | Screen turn, games | Spontaneous rotation of the interface |
| GPS module | Geolocation accuracy | Long search for satellites, coordinate error |
| Light sensor | Autobrightness | The screen is too dim or bright |
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Proper operation of the proximity sensor is critical for comfortable calls. If the test in the engineering menu shows a failure, try clearing the area above the speaker or calibrate the sensor through the Engineering Menu app (if available in your version of MIUI).
Diagnostics of battery and charging system
Battery status is one of the top questions when buying a used phone. Xiaomi's engineering menu has a Battery section that shows current status. However, more accurate information can be obtained by analyzing the behavior of the phone under load. Battery often provides information about charging cycles and current voltage.
Pay attention to the temperature. During tests, especially when checking the processor or camera, the phone may get hot. This is normal, but the heating should not be local (at one point) or excessive (when you can not hold in your hand), a sharp jump in temperature can indicate problems with the power controller or the battery itself.
Check the USB Type-C charging connector. Insert the cable and move it. If the charging goes missing, it appears, the connector is loose or oxidized. There may also be a charging current test on the menu to show whether the actual power is the declared power (for example, 33 W, 67 W or 120 W).
⚠️ Attention: Battery bloating is a dangerous defect. If the back of the phone has moved or the screen is pushed out of the frame, immediately stop using the device.
Performance Analysis and Stress Test
Although the engineering menu offers basic tests, it is better to use specialized benchmarks such as AnTuTu or Geekbench to fully assess performance. CIT-menus are test «CPU» Or "Performance," which loads the processor. FPS (frames per second) and temperature.
If a Xiaomi phone starts to brake, reboot or fails in simple tests, it is a red flag, especially for models with Snapdragon or Dimensity processors, which must cope with load without failure.
Check the NFC module. You should have a card reading test on the menu. You should have a bank card or a transport card attached to the back cover. If the phone vibrates or makes a readout sound, the module is in good working order. This is important for contactless payment and using the phone as a key.
Authentication and status of the guarantee
The market is full of copies that are visually almost indistinguishable from the original, but have cheap hardware inside. To check the authenticity of a Xiaomi phone, use the official service on the manufacturer's website. IMEI-code that can be found on the box or in the settings.
Go to the official verification site and enter IMEI. The system will show the device model, activation date and warranty status. If the site says "Invalid IMEI" or the model does not match yours (for example, instead of the Redmi Note 12 Redmi 9A), you are facing a fake or a device with re-sold memory.
Also worth checking is the bootloader's unlock status, and the engineering menu on the "Mi Unlock Status" item should say "Locked." If "Unlocked" status means that the previous owner has interfered with the system, which often loses warranty, has stripped down functionality (e.g., the NFC banking system does not work), and can be stolen.
What is the Unlocked status in MI Unlock Status?
Can I check out a Xiaomi phone without an engineering menu?
Why is the #6484## code not working?
How to reset the test results in the engineering menu?
A comprehensive check of Xiaomi phone takes no more than 10-15 minutes, but saves you from a lot of problems in the future. Use built-in tools, trust the facts, not the words of the seller, and your smartphone will last a long time. Remember, there are no perfect used devices, but hiding serious defects is a sign of bad faith.