U049B code meaning
Invalid Data Received From Tachograph Module
What U049B means
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.
U049B at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U049B
- Speedometer or tachograph speed missing or erratic
- Cruise control, speed limiter or shift behaviour affected
- Tachograph fault message
Common causes of U049B
- Most likelyTachograph calibration or parameters not matching the vehicle, e.g. after a tire or axle change
- PossibleFaulty motion sensor or sensor wiring producing implausible speed values
- Less likelyInternal fault of the tachograph unit
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Tachograph module
What each part of U049B means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 9B | The exact fault in that area. |
What to do next
- Note U049B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U049B
What does U049B mean?
U049B means "Invalid Data Received From Tachograph Module". U049B is set when the tachograph still transmits but its data are rejected. It is a generic code, so it means the same on every make.
Is it safe to drive with U049B?
U049B does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U049B fail an emissions test?
U049B is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U049B to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U049B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.