Fix: Modem reported error code 651 in Windows 11, 10

Several Windows users have recently complained that when they tried to connect a modem on their PC to access the Internet, it produced an error stating that the modem (or other connected device) reported a problem with error code 651 and was not Allow connection to the system.

This problem may be caused by system or modem failure, outdated network card driver, automatic adjustment option not disabled, etc.

Keeping all these things in mind, this article will show you various fixes that may be able to resolve this issue and allow the user to connect a modem to the system.

If you encounter similar issues, please continue reading to learn more.

Before that, you can try these solutions given below -

1. Restart the system a few times and check if the issue is resolved.
2. Try connecting the modem to another system to check if the problem is system related.
3. If not, try connecting to another modem (different connection) to see if there are any issues with the modem.
4. Check whether the cables are loose or damaged/damaged.
5. Try restarting the system in safe mode over the network and see if it works!

Fix 1 – Disable the Auto-Tune feature

To improve network performance, Windows has added the Auto-Tune feature that monitors network latency, bandwidth, and other parameters. Enabling this feature may also cause the above issues.

Therefore, we recommend that users disable the auto-tuning feature on their systems. Let’s see how it can be done using the simple steps given below.

Step 1: Press the Windows X keys simultaneously to view the Context menu for the Start button.

Step 2: Then, hit the R key on your keyboard to open the "Run" command box.

Step 3: Type cmd in the text box of the run window, and then press CTRL SHIFT ENTER at the same time Key to open command prompt as administrator.

Note: You can also continue accepting the UAC prompt by clicking Yes.

Step 4: Copy and paste the command given below into the command prompt window you just opened and press Enter to execute it .

Netsh interface tcp set global autotuning=disabled

Step 5: This will disable the auto-tuning feature on your system.

Step 6: Once completed, close the command prompt window.

Now check if you can establish an Internet connection by connecting the modem to your system.

Fix 2 – Reset TCP/IP on Windows systems

Both TCP and IP are responsible for establishing reliable connections between computers that can easily interact with each other. TCP allows packets to be sent from one device to another by using an IP address that contains device information.

This type of problem is common when modifying TCP/IP settings. So, follow the steps below to reset TCP/IP.

Step 1: Press the Windows and R keys on your keyboard at the same time, open the Run box.

Step 2: Next type cmd in the "Run" box and then hit the CTRL SHIFT ENTER keys simultaneously to open Elevated command prompt.

Step 3: Click Yes on the User Access Control prompt to continue.

Step 4: Enter the following lines at the command prompt and press Enter to execute.

netsh int ip reset reset.log

Step 5: This will reset TCP/IP on the system.

Step 6: Once completed, close the command prompt and restart the system and check if the issue is resolved.

Fix 3 – Disable Internet Protocol Version 6 IPv6

Try disabling IPv6 on the system from the Ethernet adapter’s Network Connections page and check if that resolves the issue.

Please follow the steps below.

Step 1: Press the Windows and R keys simultaneously to open the Run command box.

Step 2: Type ncpa.cpl in the "Run" box and press Enter to open Network Connection page.

Step 3: Right-click on the EthernetAdapter and click Properties# from the context menu ##,As follows.

Step 4: Once the Ethernet Properties window opens, uncheck the

Internet Protocol Version 6 (IPv6) checkbox and click Sure.

Step 5: This will disable IPv6 on the system for use with Ethernet.

Now try to establish a connection to your system and check if it works.

Fix 4 – Run the Network Adapter Troubleshooter

Windows systems have a built-in program called the Network Adapter Troubleshooter, which attempts to detect and fix network-related issues.

Let’s see how to run the network adapter troubleshooter on your system.

Step 1: Press the Windows and R keys simultaneously to open the Run box.

Step 2: Enter control.exe /name Microsoft.Troubleshooting in the Run box, and press Enter to open ## directly #Troubleshoot page.

Step 3: Select the

Additional troubleshooting options by clicking as shown below.

Step 4: Scroll down the page and click

Run to perform Network Adaptertroubleshooting as shown in the image below.

Step 5: It will start detecting issues related to the network adapter, if any issues are found, follow the on-screen instructions to fix the issue.

Step 6: Once completed, close the window and check if the issue has been resolved.

Fix 5 – Update Network Drivers via Device Manager

Outdated network drivers can sometimes cause problems that are not easily detected when troubleshooting. Therefore, we recommend users to update network drivers on Windows systems through Device Manager. Let’s see how to update it using the following steps.

Step 1: Press the

Windows Step 2: Double-click the Network Adapters option to expand it.

Step 3: This contains all available network adapters on the system.

Step 4: Right-click the

Ethernet

WAN miniport

and click

Update Driver from the context menu, as shown below shown in the screenshot. Step 5: Follow the on-screen instructions to complete the update process.

Step 6: Once completed, close Device Manager.

Fix 6 – Try to re-register the raspppoe.sys file

The file named raspppoe.sys is located in the folder system32 on your Windows system and is responsible for your system and other connections Better communication between devices. So let's re-register the raspppoe.sys file and if there is any problem with it, it will fix it.

Step 1: Press the

Windows

key and type

cmd.

Step 2: Then, Right-click the Command Prompt

application and select

Run as administrator from the list,As follows. Step 3: Click Yes"Accept any UAC prompts that pop up to continue.

Step 4: After opening the command prompt, type

regsvr32 raspppoe.sys

and press Enter

.

Step 5: This will re-register the raspppoe.sys file.

Step 6: Next, close the command prompt window and restart the system.

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