U3556Hydrogen Tank C Valve Control Circuit
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- U3556 is the control circuit code for the valve on tank C, the third tank found only on three-tank layouts such as the Nexo or the current Mirai. On the Mirai the two crosswise tanks behind the long central one are the smaller ones, so losing one costs only part of the range. That makes the fault easy to overlook while driving. The controller recognises an electrical fault in the valve drive directly and stores U3556, whereas a valve that sticks mechanically only shows up as missing hydrogen, which Hyundai's patent finds by comparing supply with consumption. Check coil, connector and driver first. No manufacturer documents U3556 publicly. Tank C stays shut; expect a warning and less range. The enable path of the same valve is U3557.
- What you may notice
- Hydrogen system warning
- Range noticeably shorter after a full fill
- Likely causes
- LikelyWiring or connector fault at the tank C valve
- PossibleValve coil open or shorted
- RareDriver stage for valve C faulty
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €100 – €5,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.