U049BInvalid Data Received From Tachograph Module
- Generic OBD-II code · Network
- How the car detects it
- 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.
- What you may notice
- Speedometer or tachograph speed missing or erratic
- Cruise control, speed limiter or shift behaviour affected
- Tachograph fault message
- Likely causes
- LikelyTachograph calibration or parameters not matching the vehicle, e.g. after a tyre or axle change
- PossibleFaulty motion sensor or sensor wiring producing implausible speed values
- RareInternal fault of the tachograph unit
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €100 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.