This code means that the tachograph has detected a security breach while authenticating a tachograph card in slot 2 (Driver 2).
Code 65 appears when the tachograph is unable to successfully verify the identity of a card inserted into slot 2. Although described as a security breach, this typically indicates a failed authentication check rather than deliberate misuse. In many cases, the issue may lie with the tachograph unit itself rather than the driver card.
When this message is shown, the card should be removed and inserted again to allow the tachograph to repeat the authentication process. The card should be checked for visible damage and confirmed as valid for use in slot 2. Where possible, the driver can try the same card in a different vehicle, which can help determine whether the fault is card-related or linked to the tachograph.
If Code 65 continues to appear after these checks, it should taken to an authorised tachograph centre for investigation.
https://www.gov.uk/find-approved-tachograph-centre-at