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Home / DTC / U019A — Lost Communication With Tachograph Module

U019A — Lost Communication With Tachograph Module

Detailed page for trouble code U019A.

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U019A

Generic U — Network/User

Lost Communication With Tachograph Module

Brand: Generic
Type: U — Network/User
Views: UK: 10 EN: 22 RU: 19
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Page language: EN

Causes

  • Blown fuse or removed power to tachograph module
  • Poor or missing ground at tachograph module
  • Damaged, corroded or disconnected connector or wiring harness to the tachograph
  • CAN/data bus wiring fault (short to battery/ground, open, high resistance)
  • Bus termination missing or incorrect (improper resistance)
  • Module gone into bus-off state or firmware fault

Symptoms

  • Tachograph (digital logger) not recording or not powered
  • Warning lamp or message on instrument cluster about tachograph or logging system
  • Other modules reporting lost communication with tachograph (additional U-codes)
  • Intermittent loss of tachograph data or intermittent warnings
  • No response from tachograph when queried with a scan tool
  • Associated systems that rely on tachograph data behave incorrectly or show errors

What to check

  • Read stored and pending DTCs and freeze-frame data with a capable scan tool; note time stamps and related U-codes
  • Verify battery voltage and ignition voltage at vehicle (12V present and stable)
  • Check relevant fuses and relays for the tachograph circuit
  • Visually inspect tachograph connector and wiring for corrosion, bent pins, damage or water ingress
  • Check for other modules reporting CAN bus errors or bus-off condition
  • Attempt to communicate with the tachograph module via OEM scan tool; note whether it responds

Signal parameters

  • Network: typically CAN (ISO 11898) or manufacturer-specific vehicle bus
  • CAN idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (single-ended); differential ≈ 0 V at idle
  • Dominant state: CAN_H ~3.5 V, CAN_L ~1.5 V (differential ≈ 2.0 V)
  • Typical data rates: 125 kbps, 250 kbps or 500 kbps (vehicle-specific)
  • Termination: two 120 ohm resistors in parallel → ~60 ohms across CAN_H to CAN_L
  • Expected message behavior: periodic tachograph messages at specific intervals (vehicle/manufacturer dependent)

Diagnostic algorithm

  1. Verify and record DTC U019A and any related codes. Note if code is current, intermittent, or historic.
  2. Use OEM or capable scan tool to attempt direct communication with tachograph. If the module responds, proceed with functional checks; if not, continue diagnostics.
  3. Verify battery/ignition voltage at the tachograph connector and check relevant fuses/relays. Repair any power or fuse issues and retest.
  4. Visually inspect connectors and wiring for corrosion, damage, pin push-out, or water ingress. Repair or replace as required.
  5. Measure CAN_H and CAN_L voltages at the tachograph connector with ignition ON, engine OFF. Confirm idle voltages, dominant state, and differential. Compare to known-good values.
  6. Check termination resistance across CAN_H and CAN_L (approx. 60 ohms). Repair missing or shorted termination resistors.
  7. Scan for bus-off conditions or high error frames on the bus. If a module is causing bus-off, isolate by disconnecting suspect nodes one at a time and re-checking bus health.
  8. Inspect wiring continuity between tachograph and other network nodes (ECU, gateway). Repair any opens or shorts (to ground or battery).
  9. If wiring and bus are OK, check module configuration and software level; reflash or reprogram per manufacturer service information if required.
  10. If the module fails to respond after power/communication checks and software attempts, consider replacing the tachograph module. After repair or replacement, clear codes and perform road test to confirm communication stability.
  11. Document repairs and verify no additional related codes remain.

Likely causes

  • Blown fuse or loss of power/ground to tachograph module
  • Connector corrosion, bent pins, or poor pin contact
  • CAN/data-bus wiring fault (open or short) between tachograph and ECU network
  • Bus termination problem or bus-off condition preventing messages
  • Failed tachograph module or software/parameter incompatibility

Fault status

⚠️ Status
Stored when the vehicle network detects no valid responses or messages from the tachograph module for a defined period, indicating loss of communication between the tachograph and other control modules.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1–3 hours
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