To preface, most Solo 401k plans are not controlled group plans. To see if you have or need a controlled group plan, please see: Controlled Group Rules.
If you do have a Controlled Group Plan, read the following to identify important information in your plan.
Access Your Plan Documents
Log into your Solo 401k dashboard at https://app.solo401k.com. Then pull up your documents. Click on your initials in the top right corner of the screen and select “Documents”.
Select your plan documents that will be labeled something similar to: Solo 401k Plan & Trust_ Controlled_Group
Once that has been located, download or view the file.
Review Controlled Group Information
The first place you'll see Controlled Group information is in your Summary Plan Description, which starts on page 5 of your document package.
Scroll to page 8 and you’ll see the businesses in your Controlled Group listed under “Who may participate?”:
You can contribute earnings to your Solo 401k from any business in your Controlled Group that is listed in your Solo 401k plan documents.
Next - scroll to your Adoption Agreement, which starts on page 25 of the 401k document package.
Scroll down to Page 26, item A9 where your controlled group information will be listed: