Thanks to OddAbbreviations5749 from Reddit (https://old.reddit.com/r/RealTesla/comments/1cn9geh/teslas_10q_from_q32023_warned_this_investigation/)
You can find this 10Q here: https://www.sec.gov/Archives/edgar/data/1318605/000162828023034847/tsla-20230930.htm
Scroll down to page 24, "Certain Investigations and Other Matters".
The relevant "Ctrl+F" is:
Separately, the Company has received requests for information, including subpoenas, from the DOJ. These have included requests for documents related to Tesla’s Autopilot and FSD features. Additionally, the Company has received requests for information, including subpoenas from the DOJ, regarding certain matters associated with personal benefits, related parties, vehicle range and personnel decisions. To our knowledge no government agency in any ongoing investigation has concluded that any wrongdoing occurred. We cannot predict the outcome or impact of any ongoing matters. Should the government decide to pursue an enforcement action, there exists the possibility of a material adverse impact on our business, results of operation, prospects, cash flows, financial position or brand.