VDO Tachograph Error Codes

This code means that the VDO tachograph has detected that the additional, independent motion signal is missing or not available.

Code 81 is generated when the tachograph is unable to receive a valid secondary motion signal. This signal is used as a cross-check to confirm vehicle movement data and its absence is treated as a system fault rather than a driver issue. The tachograph itself is not necessarily the source of the problem.

Common causes include issues on the vehicle CAN bus, interruptions to the data connection between the tachograph and the vehicle systems, or power supply irregularities affecting CAN bus components. In some cases, external factors can also contribute — for example, the vehicle operating in an area where supporting signals (such as GPS-based inputs) are temporarily unavailable.

Issues that cause code 81 to appear are likely to cause the recorded data to be inaccurate, which is why it’s important to resolve them quickly.

If Code 81 is repeatedly displayed, the vehicle should be referred to an approved tachograph centre for investigation. As the fault may originate outside of the tachograph head unit itself, authorised diagnostic checks are required before the vehicle is returned to normal operation.

https://www.gov.uk/find-approved-tachograph-centre-at

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

Code 34 appears when the tachograph cannot eject the card because certain operating conditions are not met. Most commonly, this happens while the vehicle is moving, during an active data download, or while the tachograph is actively reading from or writing to the card. On ADR versions, the message can also appear if the ignition is switched off. In some cases, the message is shown when a card ejection is requested immediately after the card has been read correctly, such as straight after insertion or following a restart during activation.

Before taking further action, the driver should check whether the vehicle is still in Trip mode and, if so, stop safely before attempting to eject the card again. It is also important to confirm that no data download is currently in progress and, for ADR vehicles, that the ignition is switched on. In many cases, simply repeating the procedure once these conditions are met will resolve the issue.

If the message continues to appear despite these checks, the issue should not be ignored. Operators should arrange for the vehicle to be inspected by an approved tachograph workshop https://www.gov.uk/find-approved-tachograph-centre-at

Error 20 relates to a motion sensor fault, which can affect how vehicle movement, speed and distance are recorded and will cause issues during roadside checks or compliance reviews.

To make sure this is a genuine fault, drivers should turn the vehicle ignition off and back on and see if the error clears. Additionally drivers can check the cables connected to the tachograph for loose or incorrect connections.

If the error remains, the vehicle should be checked at an approved tachograph centre:
https://www.gov.uk/find-approved-tachograph-centre-atc

Further details on the error can be found here:
https://www.dtco-user.com/errorcodes/2.0/index.php?lng=en&site=20-29