The EFTPS PIN cannot be used to file the 941 forms. To electronically file the forms, the IRS requires a special e-file PIN.
When filing the 941 form, you have the option of filing as a Taxpayer or Reporting Agent. If filing as a Taxpayer, a 10-digit PIN will be required to electronically file the forms. To file as a Reporting Agent will require a 5-digit PIN and a 6-digit EFIN.