FRITZ!Box 3370 – Service - Knowledge Base

FRITZ!Box 3370 – Service

FRITZ!Box indicates numerous DSL connection errors

You are experiencing problems with your DSL connection due to numerous errors on the FRITZ!Box's end or at your DSL Internet service provider's exchange. As a result, Internet access over the FRITZ!Box is very slow (when you open web pages or download files, for example) or problems occur when you conduct Internet calls or play back videos (for example IPTV or video on demand).


  • The throughput and stability of the DSL connection primarily depend on length and quality of the access line. Faults in the cabling or problems with the Internet service provider's exchange (DSLAM) can also affect it.

Important:Some of the settings described here are only displayed if the advanced view is enabled in the user interface. The configuration procedure and notes on functions given in this guide refer to the latest FRITZ!OS.

Simply proceed as described below. After each measure, check whether the issue persists.

1 Checking the cabling

It is often difficult to recognize mistakes in the cabling and they can remain unnoticed for a long time. Therefore, check the wiring in your home:

  • Make sure that the FRITZ!Box is correctly connected to your DSL line. Remove the following:
    • if you have an IP-based line: the DSL splitter,
    • all cable extensions,
    • unused cables and telephone jacks,
    • additional electrical components (for example surge protection, automatic extension outlets).

2 Installing the latest FRITZ!OS for the FRITZ!Box

Installing the latest FRITZ!OS makes your FRITZ!Box compatible with the latest DSL technology used by DSL providers in their DSL exchanges:

3 Increasing the interference resistance

Increase the interference resistance of your DSL connection. This reduces the number of errors due to brief disturbances on the DSL line:

Note:Increasing the interference resistance of the DSL connection can reduce the throughput of the DSL connection. However, this can increase the speed and quality of Internet access, as they are not affected by retransmissions.

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "DSL Information" in the "Internet" menu.
  3. Click on the "Line Settings" tab.
  4. Move one of the controls under "Receive direction" one step farther to the left towards "Maximum Stability".

    Important:If you move the control too far towards "Maximum Stability", with some DSL lines you will no longer be able to establish a DSL connection. Therefore, do not select the setting "maximum stability" right away. Instead, push the controls gradually to the left in order to determine the best setting for your DSL line.

  5. Click "Apply" to save the settings.
  6. Click on the "DSL" tab.
  7. Check in the "Error Counter" section whether "Not Remediable Errors" (CRC) occur in the FRITZ!Box or the DSL exchange when you use the Internet.
    • If numerous errors still occurred during the last 15 minutes:
      • Repeat steps 3 - 7 until no further errors occur.

4 Checking the DSL line

There may be a problem with the DSL line. Since it may take a while for your DSL provider to check your line, you may be charged for the service, and our experience shows that there is often a problem with DSL lines even if they have been checked by your provider, proceed as follows:

  • Check whether you also experience problems with your Internet connection if you use a different DSL modem on your DSL line,
    • or,
    • test whether you experience problems when you use the FRITZ!Box to access the Internet on a different DSL line (for example at your neighbor's).
    • If you also experience problems when you use a different DSL modem on your DSL line, or if you do not experience problems when the FRITZ!Box establishes a DSL connection on a different line:
      • Have the DSL provider check the DSL line.

        ATTENTION!Your DSL provider may charge you for checking your DSL line. Ask your DSL provider about charges in advance!