Post

Posted
By Joey
8 min read

Deep Dive: Debugging “No Signal” on Your Xiaomi Device – From Dialer Codes to ADB Logs

A “No SIM” or “No Signal” error on your Xiaomi phone can bring your mobile communication to a screeching halt. While basic troubleshooting steps like rebooting or re-inserting the SIM card are common knowledge, sometimes the problem runs deeper, requiring a more technical approach. This guide will walk you through advanced methods to diagnose and potentially resolve SIM connectivity issues on your Xiaomi device, leveraging built-in diagnostic tools and the power of Android Debug Bridge (ADB).

Current Date: May 18, 2025

Target Audience: Tech-savvy users, developers, and anyone comfortable with more advanced Android troubleshooting.

Phase 1: The Essential Groundwork – Beyond the Obvious

Before diving into complex diagnostics, ensure you’ve covered these expanded basics:

  1. Thorough SIM Card Check:
    • Physical Inspection: Remove the SIM. Examine it for any scratches, cracks, or dirt on the gold contacts. Clean gently with a soft, dry cloth. Check the SIM tray for any damage.
    • Cross-Device Test: Place your SIM into another known-working phone. If it fails there too, the SIM card itself is likely the culprit. Contact your carrier for a replacement.
    • Test Another SIM: Insert a different, known-working SIM card into your Xiaomi device. If this SIM works, your original SIM or specific carrier settings related to it might be the issue.
  2. Carrier & Account Status:
    • Billing: Confirm your account is in good standing with no overdue payments leading to service suspension.
    • Network Outages: Check your carrier’s website or social media for any reported local network outages.
    • Device Compatibility: Ensure your Xiaomi device isn’t blacklisted (e.g., reported lost or stolen) and is compatible with your carrier’s network bands, especially if it’s an imported model.
  3. Software & Settings Review:
    • MIUI Updates: Go to Settings > About phone > MIUI version and check for any pending system updates. These often include modem and radio firmware updates.
    • Network Settings Reset: Navigate to Settings > Connection & sharing > Reset Wi-Fi, mobile networks, and Bluetooth. This will clear saved network configurations.
    • Manual Network Selection: Go to Settings > SIM cards & mobile networks > [Your SIM] > Mobile networks. Disable Automatically select network and manually choose your carrier. If already manual, try automatic.
    • Preferred Network Type: Under SIM cards & mobile networks > [Your SIM] > Preferred network type, try switching between Prefer LTE, Prefer 3G, etc. An unstable 4G/5G signal might be causing issues, and switching to 3G could provide stability.

Phase 2: Unlocking On-Device Diagnostics with Dialer Codes

Xiaomi devices have hidden “secret codes” that can be entered into the phone dialer to access diagnostic menus. These are invaluable for quick hardware checks.

  1. CIT (Hardware Test) Menu:

    • Code: *#*#64663#*#* (sometimes *#*#MIUI#*#* which translates to *#*#6484#*#*)
    • Function: This opens the main hardware testing suite. You can test various components, including:
      • SIM Card Test (Single/Dual SIM): This is your primary interest here. It should indicate if the SIM card(s) are detected and recognized.
      • Other tests include screen, touch, sensors, Wi-Fi, Bluetooth, etc.
    • Alternative Access: If the code doesn’t work, try Settings > About phone > All specs. Tap repeatedly (5-7 times) on “Kernel version.” This often launches the CIT menu.

  2. Testing Menu (Phone Information):

    • Code: *#*#4636#*#*
    • Function: This menu provides detailed information about:
      • Phone information [SIM1/SIM2]: Here you can see current network, signal strength (in dBm and asu – lower dBm is better, e.g., -70dBm is stronger than -100dBm), voice/data network type, IMEI, and run ping tests. Check if the “Mobile Radio Power” is enabled. You can also sometimes set the preferred network type from here.
      • Battery information: Health, temperature, voltage.
      • Usage statistics: App usage times.
      • Wi-Fi information: Wi-Fi status, network configuration.

  3. IMEI Check:

    • Code: *#06#
    • Function: Displays your phone’s IMEI (International Mobile Equipment Identity) number(s). If this is null, blank, or showing an obviously incorrect number, it indicates a serious software or hardware issue (potentially a corrupted EFS partition) that will prevent network registration.

Interpreting Dialer Test Results:

  • SIM Not Detected in CIT: If the CIT menu shows the SIM as not present or faulty, and you’ve confirmed the SIM works in another phone, this points towards a potential hardware issue with your Xiaomi’s SIM reader or motherboard.
  • Low/Fluctuating Signal Strength in Testing Menu: This could indicate antenna issues, modem problems, or severe external interference.
  • Network State “Unknown” or “Emergency Calls Only”: Suggests the phone is struggling to register on the network.

Phase 3: Advanced Debugging with ADB (Android Debug Bridge)

ADB allows you to interface with your Android device from a computer, offering powerful logging and diagnostic capabilities.

Prerequisites:

  1. Install ADB & Fastboot: Download the Android SDK Platform Tools from the official Android developer website and extract them to a known folder on your PC.
  2. Enable Developer Options on Xiaomi: Go to Settings > About phone. Tap on “MIUI version” repeatedly (about 7-10 times) until you see “You are now a developer!”
  3. Enable USB Debugging: Go to Settings > Additional settings > Developer options. Enable “USB debugging” and, if present, “USB debugging (Security settings)” (this might require a Mi Account and SIM card with data).
  4. Connect Your Phone: Connect your Xiaomi device to your PC via USB. Authorize the USB debugging connection on your phone when prompted.
  5. Open Command Prompt/Terminal: Navigate to the folder where you extracted the Platform Tools.

Key ADB Logging Commands for SIM/Network Issues:

  1. adb devices

    • Purpose: Verifies that your device is connected and recognized by ADB. It should list your device ID.

  2. adb logcat (The All-Seeing Eye)

    • Purpose: Provides a real-time stream of system messages, including radio and telephony events. This is extremely verbose, so filtering is essential.
    • Basic Usage: adb logcat
    • Filtered Usage (Recommended):
      1

      adb logcat -E "RILJ|Radio|Telephony|GSM|SignalStrength|SIM|Modem|DataConnection|NetworkController"

      (On Windows, you might use findstr instead of grep -E, or use PowerShell which has Select-String)

      1

      adb logcat | Select-String -Pattern "RILJ|Radio|Telephony|GSM|SignalStrength|SIM|Modem|DataConnection|NetworkController"
    • What to look for:
      • RIL (Radio Interface Layer) messages: Errors like “RIL_REQUEST_SETUP_DATA_CALL failed,” “SIM_STATE_ABSENT,” “RADIO_NOT_AVAILABLE.”
      • Signal strength changes: Look for dBm values and how they fluctuate.
      • Network registration attempts: Messages related to attaching to GSM/LTE networks.
      • SIM status events: INTERNAL_SIM_REJECTED, SIM_STATE_READY, SIM_STATE_PIN_REQUIRED, etc.
      • Modem crashes or resets.

  3. adb shell dumpsys telephony.registry

    • Purpose: Dumps detailed information about the telephony system, including current network state, service state, signal strength, cell location, connected operator, IMEI/SV, etc.
    • Usage: adb shell dumpsys telephony.registry > telephony_dump.txt (saves output to a file for easier review).

  4. adb shell getprop (Querying System Properties)

    • Purpose: Retrieves specific system properties related to the radio and network.
    • Useful Properties:
      • gsm.operator.alpha (Connected operator name)
      • gsm.operator.numeric (Operator MCC/MNC)
      • gsm.network.type (Current network type)
      • gsm.sim.state (SIM card state)
      • ril.signalstrength.dbm (Signal strength in dBm)
    • Usage: adb shell getprop gsm.sim.state

  5. Bug Reports (Comprehensive Logs):

    • Purpose: Generates a detailed report containing logcat, dumpsys, and other diagnostic information.
    • How to generate:
      • From Developer Options on your phone: Tap “Take bug report.”
      • Via ADB: adb bugreport bugreport.zip (This creates a zip file with the report).
    • Analysis: Unzip the file (usually bugreport-<build_id>-<timestamp>.txt inside) and search for relevant keywords. This is dense but often contains crucial clues.

Interpreting ADB Logs: This can be challenging and often requires experience. Look for error messages, unexpected state changes, repeated failures in registration or data connection attempts. Correlate timestamps in the logs with actions you perform on the device (e.g., toggling airplane mode, trying to make a call).

Phase 4: Other Advanced Considerations

  • APN Settings: Incorrect APN (Access Point Name) settings primarily affect mobile data but can sometimes influence network registration.
    • Settings > SIM cards & mobile networks > [Your SIM] > Access Point Names (APNs).
    • Verify the settings with your carrier or try resetting to default.
  • Modem Firmware (Advanced & Risky):
    • If you’ve flashed custom ROMs or suspect modem firmware corruption (especially after a botched update), you might consider re-flashing the correct modem firmware for your specific Xiaomi model and region.
    • Caution: This is a high-risk procedure. Using incorrect firmware can brick your device. Only attempt this if you understand the risks and have reliable sources for firmware files (e.g., official fastboot ROMs, reputable XDA Developers threads).
  • EFS Partition: This partition stores critical data like your IMEI. Corruption here almost always leads to “No Signal.” Repairing it is complex and often device-specific, sometimes requiring specialized tools or service center intervention. If your IMEI is null (*#06#), this is a strong possibility.

When All Else Fails: Seeking Professional Help

If after these exhaustive checks, your Xiaomi device still refuses to connect, the issue likely lies with a hardware fault:

  • Damaged SIM card reader/slot.
  • Faulty antenna or antenna cable.
  • Problem with the radio/modem chip on the motherboard.
  • Other motherboard-level issues.

In such cases, your best course of action is to visit an authorized Xiaomi service center or a reputable independent repair technician for hardware diagnostics and repair.

Conclusion:

Debugging SIM card and network signal issues on Xiaomi devices can range from simple fixes to intricate diagnostics. By leveraging dialer codes for quick hardware checks and ADB for in-depth logging, you gain powerful insights into what’s happening under the hood. Always proceed systematically, from basic checks to more advanced techniques, and remember the importance of backing up your data before attempting any potentially risky operations like firmware flashing or factory resets. Good luck!

This post is licensed under CC BY 4.0 by the author.

© Joey. Some rights reserved.

Using the Chirpy theme for Jekyll.