Digital tachograph

Digital tachographs record driving and rest times, speed and distance travelled. When recording problems occur, the workshop must distinguish between power supply faults, faulty motion sensors, communication problems and internal device faults. Unnecessarily replacing a recording unit increases costs, while an unresolved wiring fault will cause further failures. For MAN, Mercedes and Neoplan trucks, buses and vans, both the technical specification and the applicable tachograph requirements are therefore key considerations.

Always identify parts using the vehicle's chassis number. Visual comparison or selection based solely on the model name is never sufficient. Also check the part number, type approval, software version, existing installation and required tachograph generation. A conventional first-generation digital tachograph cannot necessarily be interchanged with a second-generation smart tachograph, version 1 or 2. Smart versions use technologies including GNSS (Global Navigation Satellite System) for positioning and DSRC (Dedicated Short-Range Communications) for communication with enforcement equipment.

For more recent vehicles, the focus is on second-generation smart tachographs. The different generations and their versions are classified as follows; the introduction dates apply to new vehicles subject to tachograph requirements within the EU.

• First generation: conventional digital tachograph.
  • Version 1 (G1V1: first generation, version 1): introduced from 1 May 2006, with digital recording of driving and rest times on the driver card and in the device memory.
  • Version 2 (G1V2: first generation, version 2): introduced from 1 October 2011, with changes including a revised calculation of driving time per calendar minute.
  • Version 3 (G1V3: first generation, version 3): introduced from 1 October 2012, with enhanced security and verification of motion information using an independent second source.
• Second generation: smart tachograph.
  • Version 1 (G2V1: second generation, version 1): introduced from 15 June 2019, with GNSS position recording at the start and end of the daily working period and after every three hours of accumulated driving time, plus DSRC for remote checks.
  • Version 2 (G2V2: second generation, version 2): introduced from 21 August 2023, with features including automatic recording of border crossings and position recording when loading and unloading operations are entered.

Manufacturer-specific variants and software versions fall within this classification but do not constitute separate statutory tachograph generations. When replacing a unit, always check the version actually fitted: the vehicle may already have been retrofitted with a newer generation or version.

Check the nominal supply voltage of 12 or 24 volts, connector pin assignments, compatible motion sensors, antenna connections and communication via CAN (Controller Area Network). The tachograph receives secure motion information from a matching sensor on the transmission; correct pairing and generation compatibility are essential.

For cab-mounted installations, the available space, mountings and cable routing vary by configuration. For example, verify the installation in MAN TGX cabs XL, XLX and XXL, MAN TG3 TGX cabs GN, GM and GX, or Mercedes Actros Lang StreamSpace and Lang GigaSpace. MAN TGE and Mercedes Sprinter have their own dashboard and power supply configurations. On buses such as MAN Lion’s Coach, Mercedes Tourismo and Neoplan Tourliner, the driver's workstation layout must also be checked.

Common complaints include unexpected restarts, card reading errors, missing speed recordings, sensor conflicts and illegible printouts. Possible causes include contact resistance at power supply terminals, broken wiring near the transmission, dirty card readers or worn printer mechanisms. On smart tachographs, recurring satellite positioning errors also require checks of the antennas and wiring.

1. First, read fault codes, event data and installation information using suitable diagnostic equipment. Note when the problem occurs: during starting, driving, card insertion or printing.
2. Use a multimeter to measure the permanent power supply, any switched power supply and the earth voltage drop directly at the connections, following the vehicle wiring diagram. Use an oscilloscope or min/max recording to capture brief voltage drops during starting. Compare the readings with the manufacturer's limits.
3. Check connector locks, contact corrosion, strain relief and cable damage. Only measure continuity with the power off and the relevant electronic components disconnected in accordance with the workshop procedure.
4. Compare sensor data and vehicle speed using diagnostic equipment. Check communication lines with an oscilloscope according to the wiring diagram; the presence of a signal does not in itself prove valid secure sensor pairing.
5. Test the card readers and printer according to the manufacturer's procedure. Use approved thermal paper: an incorrect roll or feed direction can cause blank printouts without an electronic fault.

Have replacement, activation, sensor pairing, calibration and sealing carried out by an approved tachograph workshop. Before removal, secure any available legally required recording data in accordance with the applicable procedure. A replacement unit is not automatically ready for use, even if the connectors and housing fit.

Calibration depends on the recording equipment constant k, the vehicle's characteristic coefficient w and the effective tyre circumference l. The first two are expressed in pulses per kilometre, and the last in millimetres. Have the tyre size, tyre pressure and measurement conditions checked in accordance with the specified method and tolerances. Rectify power supply problems and damaged cable routing before putting the unit into service; this prevents the same fault from recurring after replacement.