Xiaomi’s mobile devices and Redmi’s sub-brand are not only affordable, but also highly customizable, and many users are unaware that a powerful diagnostic tool is hidden inside the MIUI or HyperOS operating system.
The CIT (Customer Interactive Test) is a hidden section designed to test components before selling, but it is also open to ordinary owners, allowing for deep fault diagnosis without connecting to a computer.
In this article, we’ll take a closer look at how to get into this hidden section, what tests are worth doing first, and how to interpret the data to identify iron problems in your device.
What is CIT and why is it needed?
CIT is an acronym for Customer Interactive Test, a software package built into firmware that allows you to run checks on all the hardware modules of a phone in turn, and unlike standard settings, you get access to raw sensor data.
Using this section is relevant when buying a used smartphone. Checking the touch screen for “dead zones” or the speaker for wheezing can eliminate the purchase of a defective device.
It is important to understand the difference between the engineering menu and the developer mode. If the developer mode is configured with program settings (animation speed, USB debugging), then CIT works directly with the physical components: the camera, accelerometer, microphones and communication modules.
- 🔍 Diagnostics: Identification of non-functioning modules before the warranty expires.
- 📱 Touchscreen Check: Find areas that do not respond to touch.
- 🔊 Audio test: Checking the main and conversational speakers.
- 📡 Communication analysis: Verification of work GPS, Wi-Fi and Bluetooth modules.
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The Engineering Menu is a secure diagnostic tool that does not require superuser (Root) rights to run basic tests.
The main ways of entering through system codes
The fastest and most common method of accessing hidden functions is the use of special features. USSD-They're entered in the same way that the phone number is used to call, but instead of connecting to the subscriber, the system redirects you to the diagnostic interface.
There are several combinations for Xiaomi and Redmi devices, the most versatile command is ##6484##. In some regions or older versions of firmware, code ##4636## can work, which opens the test menu, but with a less detailed list of tests.
Once the last digit (* or #) is entered, the menu should open automatically. If it does not, your carrier may be blocking the menu. USSD-request or a specific version of the shell is installed, where the input is changed, in which case, try entering the code in flight mode or through the default Phone application.
⚠️ Note: Do not change settings in sections that you do not know the purpose of (for example, radio module parameters), as this may cause loss of network signal.
There is also an alternative way for some models to type in the code ##64663##, which is common on devices assembled for the Chinese market, but can also work on global versions.
Entry through settings and security application
If you don't get the codes, you can use a graphical interface, which is more reliable because it doesn't depend on the operator's lock, and the path to the menu can vary slightly depending on the version of MIUI.
Go to the standard Security app (green zipper icon). Scroll down to "Device Check" or "Testing." In some versions, this section is hidden in the About Phone menu, where you need to click on the kernel or build version several times.
Once you run the test, it'll offer you a series of tests, and this is a simplified version of the engineering menu, where you can check the screen, the vibration, the buttons, sequentially, and then you can go to the full list of tests, and sometimes you have to click on the MIUI logo in the corner of the screen, or use the menu button.
Detailed diagnosis of the display and touch screen
One of the most important functions of CIT is to check the matrix and the touch layer, and even if the screen appears to be intact, there may be color defects or broken pixels that are invisible when viewed at a glance.
Choose the Display or Touchpanel test, and the screen will be filled with a specific color (red, green, blue, white, black) and carefully examine the surface: any points that differ in color or brightness from the main background indicate a matrix defect.
To check the touchscreen, you'll run a grid or a drawing, and you'll have to swipe all the lines, and if some part of the line doesn't return color, you've got a broken sense in that area.
Pay special attention to the edges of the screen. On models with curved edges or protective glasses 2.5D often have problems with responsiveness around the perimeter. Regular check helps to track the degradation of the sensor over time.
- 🎨 Color rendering: Checking for uniformity of illumination and absence of spots.
- 👆 Multi-touch: Checking simultaneous response to multiple touches.
- 📉 Degradation: Identification of areas with reduced sensitivity.
- 🖌️ Artifacts: Search for broken pixels on black and white backgrounds.
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When checking white, reduce the brightness to a minimum – it is easier to notice the unevenness of the backlight (the effect of “clouds”) at the edges of the screen.
Audio system and microphones check
Sound problems are a common complaint of users, and the engineering menu allows you to check each microphone and speaker separately, which is impossible to do in normal music listening mode.
In the Receiver and Speaker section, the test signals are played. You have to hear a clear sound without cracking, wheezing or interrupting. The volume has to match the level you choose.
For microphones (Main Mic, Sub Mic), the test is usually to record your voice and then play it back. Speak to different parts of the phone (bottom, top, rear) to make sure all microphones are active and transmit sound clearly, which is critical for noise cancellation and hands-free operation.
| Component | Normal work. | Signs of malfunction |
|---|---|---|
| Receiver | Clear sound in the ear | Quiet sound, hissing |
| Speaker | Loud stereo/mono sound | Wheezing at maximum, no bass |
| Main Mic | Clear voice recording | The "barrel-like" recording, silence |
| Vibration | Uniform vibration | Freaking, lack of response |
⚠️ Warning: If you hear a loud whistling or squeaking sound during a microphone test, stop the test immediately.
Why is the speaker wheezing?
Testing of communication and navigation modules
The communications section contains tools to check GPS, Wi-Fi, Bluetooth and cellular networks, which is especially useful if the navigator is floating or the phone is not catching the network well in the area of confident reception.
In the GPS test, you'll see a list of visible satellites and their signal. If the phone is cold (it hasn't turned on for a long time), the search can take up to 2-3 minutes.
Wi-Fi and Bluetooth have data tests available. The system will try to find available networks or devices around. If the list is empty, even though the router is turned on, maybe the problem is in the antenna module or software driver failure.
It is worth mentioning the test separately. SIM-It lets you check if the phone sees the card, if it reads the card. IMSI And if you can log in, it helps you know if you need a SIM card replacement or a problem with your phone slot.
☑️ Diagnostics GPS
Analysis of sensors and control buttons
The modern smartphone is full of sensors: accelerometer, gyroscope, sensor approach, light, failure in their work leads to the fact that the screen does not go out during a conversation or autoturn works chaoticly.
In the Sensor section, you can see raw data from all the sensors in real time. When you tilt the phone, you should see the change in values. The proximity sensor is checked by putting your hand to the top end, the screen should go out.
The Key test allows you to check the physical response of the volume and turn on buttons. Press them, the indicator should light up on the screen, and if the button sticks or doesn't work the first time, it's a mechanical wear signal.
It also checks the LED light (if it's in the model) and it should flash different colors, and the lack of light may indicate a burned LED or software lock.
Remember that some sensors require calibration. The engineering menu often has a Calibration button for the accelerometer. Put your phone on a flat surface and start calibrating if the autorotation is not working properly.
Frequent problems and methods of their elimination
Even if the tests show errors, it doesn't always mean a failure. Often the problem is a software failure or application conflict. The first step should always be to restart the device.
If the touchscreen doesn't work in one zone, but the glass is physically intact, try clearing the system cache or resetting to factory settings. Software "glitch" calibration is sometimes solved only by a complete reset.
In the case when the communication tests show the absence of a signal when the serviceable SIM-If you have a map, you should check if the antenna contact inside the case has unstuck (relevant after the falls.
⚠️ Note: If after resetting the tests continue to show critical errors (for example, the absence of all networks or complete inoperability of the touchscreen), a hardware breakdown is likely.
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Software errors in tests are often fixed by resetting settings, but physical damage requires replacement of components in the service center.