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28th November 2019

A local lady contacted us to ask if we knew why the speedometer in her 2011 Mercedes-Benz Atego horsebox had stopped working. Following a discussion as to the history of the vehicle, we suggested that she bring the vehicle in. Using our VDO tachograph diagnostic equipment, we ascertained that the tachograph back-up battery had not been replaced at two-year intervals as is recommended. The battery had eventually failed and this had caused the data to be erased from the tachograph head, rendering the tachograph unusable. The speed signal was therefore not being transmitted by the tachograph to the speedometer.

As this vehicle was used for personal leisure pursuits, rather than as a business vehicle, bi-annual tachograph calibrations were not required. The back-up battery would have been replaced at these calibrations but these had not been carried out.

Following replacement of the tachograph with a new unit, the speedometer operation was restored. We have also added this lady’s vehicle details to our reminder system, this will ensure that we contact her in two years’ time to arrange replacement of the battery and prevent another tachograph failure.