I admit that I haven’t experienced the problem you are having but a google search yielded the following on the Sewing Machines Plus website;
How to Fix Brother Sewing Machine Error Code E6
<dl class="smp4" style="font-size: 16px; box-sizing: border-box; margin-bottom: 20px; caret-color: rgb(49, 49, 49); color: rgb(49, 49, 49); font-family: Lato, sans-serif; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); -webkit-text-size-adjust: 100%;"><dt style="box-sizing: border-box; line-height: 1.42857143; font-weight: bold; margin-top: 1em;">Q: What does E6 error message mean?</dt><dd style="box-sizing: border-box; line-height: 1.42857143; margin-left: 10px; font-size: medium;">A: The motor locked up because thread is tangled</dd><dt style="box-sizing: border-box; line-height: 1.42857143; font-weight: bold; margin-top: 1em;">Q: How to fix E6 error message?</dt><dd style="box-sizing: border-box; line-height: 1.42857143; margin-left: 10px; font-size: medium;">A: Do the following:
- The upper thread could be tangled. Remove the upper thread and any loose threads. Raise the pressure foot, raise the needle to its highest position and rethread the machine.
- Remove the bobbin and bobbin case to clean any lint or loose threads. Install the bobbin case so that the projection on it aligns with the spring. Then install the bobbin into the bobbin case.
- The needle could be bent. Replace the needle making sure the flat side is facing the back
Sounds like you have done most, all of these things but it does confirm you are on the right track.
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