Galaxy S9 automatically switches to mobile data when wifi is off, won’t connect to one wifi network

One of the least known features of Samsung Galaxy devices is called Smart network switching. We think that this is the reason why one of our readers is having an “issue” right now. Smart network switch is basically a feature that allows a #GalaxyS9 to use mobile data when wifi has been disconnected or out of range. If you’re one of those who thinks this behavior on your S9 should not be happening, we suggest that you take a look at our suggestions below.

Before we proceed, we want to remind you that if you are looking for solutions to your own #Android issue, you can contact us by using the link provided at the bottom of this page. When describing your issue, please be as detailed as possible so we can easily pinpoint a relevant solution. If you can, kindly include the exact error messages you are getting to give us an idea where to start. If you have already tried some troubleshooting steps before emailing us, make sure to mention them so we can skip them in our answers.

Problem #1: Galaxy S9 automatically switches to mobile data when wifi is off or out of range

I have the lovely new Samsung S9 (not plus) on O2 network. I have been experiencing a problem when it’s going from being connected to Wifi and then picking up mobile data.  I have had the phone for 3 weeks now and i am on my second handset – which is doing exactly the same. I had on the old phone a network settings refresh, new sim card and then a new handset.  New handset – old sim card that was replaced 2 weeks ago. If i put it in airplane mode ad back on again – it’s fine – but i have to do this everytime i step away from wifi. Any thoughts? I think it’s a software problem but have the latest software update installed. I can’t believe that in the entire world i am the only person to have this problem on two handsets? Any thoughts you have on this would be very much appreciated.  Else i will be going back to O2 to see what they say. Thanks. — Louise Umbers

Solution: Hi Louise. The problem most probably stems from a software bug that’s isolated to your carrier’s firmware build. Frankly, we haven’t encountered this issue on the S8 or S9 before. We also did not receive any reports from other members regarding this issue so we can’t say that it’s a pervasive one. If you do a quick Google search about this issue, there’s no mention of exact or similar situation at all so this may be isolated to your carrier. That the issue continues to occur even on the replacement handset is an obvious sign that the issue may only be happening for users on O2 network.

Smart network switching

Samsung Galaxy devices have a feature called Smart network switching to allow them to automatically use mobile data when wifi is disconnected or out of range. If you enabled this feature, this may be the reason why your S9 behaves the way it is right now. Basically, Smart network switch was created to save a user from the hassle of manually turning on mobile data when wifi is not available. If you don’t want this to happen, then simply turn smart network switch off. Here’s how:

  1. Open Settings app.
  2. Tap Connections.
  3. Press and hold Wi-Fi.
  4. Tap ADVANCED.
  5. Check what’s the status of Smart network switch. It should not be on if mobile data is off. If you want to turn on Smart network switch, make sure to turn on mobile data first. Otherwise, just leave Smart network switch in its current position.

Possibly not an Android issue

If the cause of your concern is not the smart network switching feature, then it’s most probably a bug. Bugs are almost always not easy to troubleshoot so a lot of trial-and-error processes have to be done to identify where they’re coming from. We don’t work for your carrier though so we don’t have the data to conclude if this bug is as pervasive as it looks to you. The most that we can do right now is to monitor the issue and see if it’s also happening with other devices from other networks. If that happens, we might have an operating system bug.

Contact your carrier

In the meantime, we want you to continue doing the workaround of toggling Airplane mode on and off. We also suggest that you let your carrier know about the problem so they can continue to find solutions for you. You can tell them that there’s no one else experiencing this problem so its most likely a carrier firmware bug and not a general Android issue.

Problem #2: Galaxy S9 won’t connect to one wifi only

Good morning from Greece! I have a problem with my Samsung S9. It can’t connect to my home WIFI. It used to connect, it connects in every other wifi, all other devices connect with no problem to my home WIFI, but not my smartphone anymore. It connects for some seconds and then disconnects and stays “saved and secured”. if I connect it again, it will stay on for some seconds and then again the same. It does that only on my home Wifi. I would appreciate any kind of help, as this thing is driving me nuts. Thank you very much!  — Kostis Gogios

Solution: Hi Kostis. There’s a number of possible reasons why this issue is happening so let’s discuss each of the possible solutions that you can try.

Refresh the cache partition

One of the common reasons for minor annoyances and bugs in Android is a corrupted system cache. This type of cache is used by Android to load apps quickly but sometimes, it can become corrupted. To ensure that the system cache is in top shape, make sure to clear the cache partition where it’s stored. Here’s how:

  1. Turn off the device.
  2. Press and hold the Volume Up key and the Bixby key, then press and hold the Power key.
  3. When the Android logo displays, release all three keys.
  4. An ‘Installing system update’ message will show for 30 – 60 seconds before the Android system recovery menu options appear.
  5. Press the Volume down key several times to highlight wipe cache partition.
  6. Press Power key to select.
  7. Press the Volume down key to highlight yes, them and press the Power key to select.
  8. When the wipe cache partition is complete, Reboot system now is highlighted.
  9. Press the Power key to restart the device.

Forget network

One of the simplest ways to fix a wifi issue is by disconnecting it first, then connecting it back again. We call this process in Android forgetting the network. If you haven’t tried that yet, follow these steps below:

  1. Open Settings app.
  2. Tap Connections.
  3. Tap Wi-Fi.
  4. Press and hold the name of your home wifi.
  5. Tap Forget network from the box that comes up.
  6. After a few moments, reconnect to your wifi and see if everything is working normally.

Reset network settings

Sometimes, a full network reset is necessary to fix wifi problems. If the issue still remains this far, make sure to reset your S9’s network settings by doing the steps below:

    1. Open Settings app.
    2. Tap General management.
    3. Tap Reset.
    4. Tap Reset network settings.
    5. Tap RESET SETTINGS button.
    6. Restart your S9 and check for the problem.



Safe mode

Rogue apps can sometimes lead to problems, including those that affect wifi network functions. To check if one of your third party apps may be to blame, make sure to boot your device to safe mode. In this mode, all third party apps will be blocked so if wifi works normally, that’s a confirmation that you have an app issue.

To boot your phone to safe mode:

  1. Turn the device off.
  2. Press and hold the Power key past the model name screen appearing on the screen.
  3. When SAMSUNG appears on the screen, release the Power key.
  4. Immediately after releasing the Power key, press and hold the Volume down key.
  5. Continue to hold the Volume down key until the device finishes restarting.
  6. When Safe mode appears in the bottom left corner of the screen, release the Volume down key.
  7. Check for the problem.

Remember, safe mode is a tool that should help you know if one of your added apps is problematic. If you think that that’s the case, then you should do trial-and-error to find what that app is. Basically, all you need to do is to uninstall apps individually and check for the problem.  Below are the specific steps that you can try:

  1. Boot your S9 to safe mode.
  2. Observe the phone and see if wifi works normally or not.
  3. If wifi works properly, then you want to go ahead and uninstall an app.
  4. Restart the phone to normal mode.
  5. Check for the problem.
  6. If the issue returns, repeat steps 1-5.

Continue doing the same cycle until you’ve identified the problematic app.

Reset settings

One other option that you can try in this situation is to reset all settings back to their defaults without actually wiping the phone, like in factory reset. Hopefully, by resetting all software settings of your device, you’ll also be wiping out an unknown bug causing your wifi problem.

To reset the settings of your S9:

  1. Open Settings app.
  2. Tap General management.
  3. Tap Reset.
  4. Tap Reset settings.
  5. Tap RESET SETTINGS button.
  6. Restart your S9 and check for the problem.

Factory reset

Finally, if the issue is still there after doing all the suggestions above, make sure that you wipe the phone clean by returning all its settings back to their defaults. Factory reset will delete your personal data as well so be sure to back them up before attempting this solution option.

To factory reset your S9:

  1. Turn off the device.
  2. Press and hold the Volume Up key and the Bixby key, then press and hold the Power key.
  3. When the green Android logo displays, release all keys (‘Installing system update’ will show for about 30 – 60 seconds before showing the Android system recovery menu options).
  4. Press the Volume down key several times to highlight ‘wipe data / factory reset’.
  5. Press Power button to select.
  6. Press the Volume down key until ‘Yes — delete all user data’ is highlighted.
  7. Press Power button to select and start the master reset.
  8. When the master reset is complete, ‘Reboot system now’ is highlighted.
  9. Press the Power key to restart the device.


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