I’ve spent years relying on USSD codes to quickly check balances, tweak call settings, and retrieve phone details. These short numeric commands have saved me time—until they stopped working, leaving me staring at an error message. If you’ve ever dialed a code and received a “Connection problem” or “Invalid MMI code” response, you’re not alone.
The truth is, USSD failures are more than just random glitches. Whether it’s a device setting, a carrier restriction, or even a recent software update, there’s always a reason—and more importantly, a fix. I’ve researched, tested, and documented the most effective ways to get your USSD codes working again. I’m not going to talk about the *#*#4636#*#* not responding when dialed.
Quick Summary
- USSD codes fail due to device settings, carrier restrictions, software issues, or incorrect formatting.
- Basic fixes include checking network coverage, restarting your phone, and verifying code syntax.
- Advanced solutions involve resetting network settings, updating firmware, clearing cache, or disabling conflicting apps.
- Carrier-specific factors (regional variations, blocked codes) may require alternative shortcodes or customer support intervention.
- Preventive measures like keeping your software updated and documenting changes can minimize future issues.
Why USSD Code Failures Happen
USSD codes may fail due to device-level issues, carrier restrictions, or user errors. Slide to reveal each cause.
- Incorrect Code Format
A missing * or # can invalidate the USSD command.
- Software Conflicts/Outdated Firmware
Android updates (especially Android 12+) may restrict USSD functions for security.
- Third-Party App Interference
Call blockers, dialer replacements, or security apps can prevent USSD execution.
- Dual SIM Conflicts
When two SIMs are active, USSD requests may be misrouted.
- Blocked or Unsupported Codes
Some carriers disable specific USSD commands due to policy or security reasons.
- Network Coverage Problems
Weak signals or outages can lead to USSD failures.
- Regional Restrictions
A code may work in one region but be unavailable in another.
- Wrong Code Entered
Device-specific or carrier-dependent codes may not work if entered incorrectly.
- Dialing Without Required SIM
Some USSD commands only function when dialed from the primary or active SIM.
🎉 Troubleshooting Complete!
You now know the common causes of USSD code failures. Use this insight to address issues effectively.
Common USSD Codes That Often Fail
These USSD codes are commonly reported as not working due to various issues:
Common USSD Codes That Often Fail and Their Fixes
| USSD Code | Purpose | Common Issue | Fix |
| *#06# | IMEI Check | No response or invalid code error | Restart device, ensure strong network signal, or try on another phone |
| *#*#7780#*#* | Factory Reset | Code does nothing or is blocked | Use the phone’s settings menu for reset: Settings > System > Reset > Factory Reset |
| *#34971539# | Camera Information | No response or partially disabled | Try third-party camera diagnostic apps or check camera permissions |
| *#0*# | LCD Display Test | Code does not launch test mode | Check if manufacturer (Samsung, Xiaomi) disabled the function; use a display test app |
| *#*#0588#*#* | Proximity Sensor Test | No response or inaccurate readings | Calibrate proximity sensor via Settings > Accessibility > Sensor Calibration |
| *#*#232338#*#* | Wi-Fi MAC Address | MAC address not displayed | Check Settings > About Phone > Status for MAC manually |
| *#*#2664#*#* | Touchscreen Test | No response or unrecognized command | Use Touchscreen Calibration Apps from Play Store |
| ##232331## | Bluetooth Test | Test mode fails to start | Toggle Bluetooth off/on, unpair and re-pair devices |
| *#*#7262626#*#* | Field Test Mode | Code not recognized | Check carrier settings or use third-party network monitoring apps |
| *#43# / #43# | Call Waiting Toggle | Network rejects request | Contact carrier for supported call settings method |
| *#31# | Hide Caller ID | Returns “connection error” | Try alternative format #31#phone-number |
| ##002# | Disable All Call Forwarding | Call forwarding remains active | Check manual settings in Call Settings > Call Forwarding |
| *#07# | SAR Level Information | Restricted by carrier | Look for SAR details in Settings > About Phone > Regulatory Labels |
| 3001#12345# | Field Mode (iOS) | Does not open on latest iOS versions | Use Settings > General > About > Network instead |
Typical Symptoms of USSD Failure
- “Invalid MMI code” or “Connection problem” message.
- The command appears to be running but never returns a result.
- The network rejects the command with an “unknown request” error.
Preliminary Troubleshooting Steps
I’ve run into USSD issues plenty of times, especially when trying to check my balance or access hidden settings on my Samsung and can work for any Android either HUAWEI, Motorola, Google pixel or even the iconic Sony. The first thing I always do is start with the basics—because more often than not, a simple fix can get things working again.
1. Check Network Coverage
I once found myself struggling with USSD codes when I had only one bar of signal. Moving to an area with better reception solved the issue immediately. If you’re on Wi-Fi calling, try disabling it. On my M33, I do this by going to Settings > Connections > Wi-Fi Calling and turning it off before dialing the USSD code.
2. Restart Your Phone
This trick works more often than you’d think. A simple restart can reset network connectivity. On my Samsung M33 5G, I just hold the power button, select Restart, and once the phone reboots, I try the USSD code again. This often fixes temporary glitches.
3. Verify Code Format
It might sound obvious, but I’ve typed in USSD codes wrong plenty of times—missing a single * or # can break the command. Always double-check the structure before hitting the call button.
4. Toggle Airplane Mode
Once, I was stuck with a persistent “Connection problem or invalid MMI code” error. I fixed it by toggling Airplane Mode on and off. On my Samsung M33 5G, I swipe down from the top, tap Airplane Mode, wait for 30 seconds, and then turn it off. This forces my phone to reconnect to the network.
5. Switch Between 2G, 3G, and 4G
This trick saved me when my USSD codes weren’t working after switching SIM cards. Some codes don’t function properly on VoLTE or 5G networks. On my Android, I went to Settings > Connections > Mobile Networks > Network Mode and switched to 3G only, then tried the code again. It worked instantly.
6. Disable Any Conflicting Services
I once installed a third-party dialer app that completely blocked my USSD codes. If you use call-blocking apps or VPNs, they might interfere. Try disabling them and then dialing the code. If you can still see the Key icon on your device that means you’re still connected to a VPN, here’s how you can remove the key icon from the device.
Deeper Device-Level Fixes
If the basics don’t work, I move on to more advanced troubleshooting. These have worked for me when USSD codes refused to run.
1. Update Phone Software
Some USSD codes stopped working for me after I updated to Android 13. But a few months later, Samsung rolled out another update, and everything started working again. If you’re having issues, check for updates under Settings > Software Update > Download and Install.
2. Reset Network Settings
When nothing else worked, resetting my network settings finally fixed my USSD errors. On Android, go to:
Settings > General Management > Reset > Reset Network Settings
This clears saved Wi-Fi networks, Bluetooth devices, and cellular settings—so make sure you reconnect everything afterward.
3. Clear Phone Dialer App Cache (Android)
Corrupt cache files can mess up USSD codes. I fixed this on my M33 by going to:
Settings > Apps > Phone > Storage > Clear Cache.
If clearing the cache doesn’t help, try Clear Data, but be aware this resets the app completely.
4. Check SIM Card Issues
Once, my secondary SIM was interfering with USSD codes. I disabled SIM 2 from Settings > Connections > SIM Manager and retried the code. It worked immediately. If you’re facing similar issues, try removing one SIM card or testing the SIM in another device.
Carrier-Level Solutions
If the fixes above don’t work, the issue might be with your carrier. Here’s how I approach it:
1. Contact Customer Support
I once struggled with a USSD code for call forwarding. After multiple failed attempts, I called my carrier, and they told me the service wasn’t available on my plan. If your code isn’t working, ask your carrier if it’s still supported.
2. Change Your Plan or Carrier Settings
Some USSD codes only work on postpaid or premium plans. I realized my prepaid plan didn’t support certain codes, so I had to switch to a different plan.
3. Use Carrier-Specific Alternatives
I once had trouble checking my balance using *123#, only to learn my carrier had changed it to #123#. Check your carrier’s website or app for the latest codes.
Preventive Measures & Best Practices
After fixing USSD issues multiple times, here’s what I do to prevent them from happening again:
✔ Keep Your Phone Updated – Bug fixes often restore broken USSD functionality.
✔ Document Working USSD Codes – I keep a list of working codes for my carrier.
✔ Avoid Third-Party Apps That Interfere – Uninstalling unnecessary dialer or call-blocking apps helped me.
✔ Stay Updated on Carrier Changes – Carriers sometimes modify or discontinue USSD services, so I check their support page occasionally.
Understanding USSD Codes and How They Work
USSD (Unstructured Supplementary Service Data) codes—often called MMI (Man-Machine Interface) codes—are sequences starting with * or #. Unlike SMS, USSD runs on GSM signaling channels, meaning it doesn’t require an internet connection and responds instantly.
- Dialing a Code → The phone sends a request to the network.
- Carrier Processing → The carrier deciphers the request and prepares a response.
- Instant Feedback → The result pops up on your screen in real-time.
This process is why USSD is fast and reliable—until it stops working.
How USSD Codes Function
- When you dial a USSD code, your phone sends a request through GSM signaling channels to your carrier.
- The network processes the request and sends back an instant response, usually displayed as a pop-up or notification.
- This two-way communication happens in real-time, meaning the session stays open until the network provides a response.
Common Uses of USSD Codes
- Checking account balance: *123#, #BAL#
- Enabling/disabling call forwarding: *21#, #21#
- Retrieving IMEI number: *#06#
- Testing network and hardware components: *#*#4636#*#* (excluded from this article as I’ve covered it before)
USSD Code Issues
Why is my USSD code not working?
USSD codes may fail due to network instability, incorrect code formatting, carrier restrictions, or software conflicts on your device. If you suspect advanced network features are disabled, you might need to check whether VoLTE or related options are enabled. For instance, if you’re dealing with VoLTE not showing up, you can investigate further with this VoLTE troubleshooting guide.
How do I fix the “Connection problem or invalid MMI code” error?
This error often appears when your phone cannot complete a USSD request due to poor signal, SIM conflicts, or temporary network issues. Try restarting your device or toggling Airplane Mode. If the problem persists, double-check your carrier’s coverage in your area.
Do all USSD codes work on every phone?
Not necessarily. Some USSD codes are exclusive to specific manufacturers (such as Samsung or Xiaomi) or carriers. If a code fails, confirm that it’s compatible with your device. Also, ensure your operating system hasn’t blocked or altered the code’s functionality after a recent update.
Can using USSD codes harm my phone?
Most USSD codes are safe, but certain ones—like those for factory resets—can erase data. Always verify a code’s purpose before dialing it. If you encounter severe software issues, such as a phone stuck in a boot loop, you might consider this Android restart-loop guide for a potential fix.
How do I know if my carrier has blocked a USSD code?
Carriers may restrict certain USSD codes to prevent misuse. If a code that previously worked now fails, it might have been disabled or blocked. Verify this by checking your carrier’s official website or contacting support. If verifications like OTP messages are also failing, consider consulting this OTP-not-receiving fix for guidance.
Can I use USSD codes without an internet connection?
Yes. USSD codes operate over GSM channels and do not require an internet connection. However, if you rely on Wi-Fi calling, network conflicts might mimic a failed USSD session. If you suspect Wi-Fi calling is interfering, try switching it off or refer to this Wi-Fi calling not working guide.
Conclusion
USSD codes are powerful tools, but failures are common due to device settings, carrier policies, or incorrect formatting. By following this troubleshooting guide, you can identify, diagnose, and fix most USSD-related issues quickly. If all else fails, contacting your carrier for clarification or alternative methods is the best approach.
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