Network, generic

U049B Invalid Data Received From Tachograph Module

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U049B is set when the tachograph still transmits but its data are rejected. In trucks and buses EU Regulation 165/2014 has the device record speed, distance and driving times from a motion sensor, and units such as Continental VDO's DTCO 4.1a pass these values on through two CAN interfaces. Engine, transmission or body controllers then rely on the tachograph speed, so implausible frames matter beyond the logbook. Allison's tech tip TT7546EN (2000 and 3000 series, 2014) shows the effect: the calibration tool of a tachograph broadcast a road speed on the data link, the TCM saw speed without output-shaft rotation, stored N/V = 0 and fell back to the performance shift schedule until calibration C142 was flashed. No maker documents U049B publicly; U019A is lost contact.

Likely causes

Tachograph calibration or parameters not matching the vehicle, e.g. after a tyre or axle change
Faulty motion sensor or sensor wiring producing implausible speed values
Internal fault of the tachograph unit

Symptoms

  • Speedometer or tachograph speed missing or erratic
  • Cruise control, speed limiter or shift behaviour affected
  • Tachograph fault message

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–1,500
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

tachograph module

Related codes

U019AP0500

References: eur-lex.europa.eu, fleet.vdo.com, static.nhtsa.gov.