Network, generic (extended)

U356B Anode Drain Valve

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

U356B is about how the drain valve behaves, not its wiring. Hyundai shows how such faults are separated: if the level in the trap fails to drop within a set time after an open command while the position sensor still reports closed, the valve is judged stuck shut; the system then limits current, drains on a schedule derived from accumulated charge and runs the stack warmer so water leaves as vapour. If the level stays low after a close command and the sensor reports open, hydrogen could escape, so the system is shut down. A dead level sensor can mimic a jammed valve; another Hyundai patent forces the valve open and watches whether a sagging cell voltage recovers to tell the two apart. In winter frozen condensate is a likely cause. No public source cites U356B; expect a warning plus reduced power or a shutdown.

Likely causes

Drain valve frozen after parking in frost
Valve sticking or not sealing due to deposits or a worn seat
Water level sensor of the trap faulty, valve itself fine
Drain line downstream of the valve blocked or iced

Symptoms

  • Fuel cell system warning, MIL on
  • Power limited, fuel cell running hotter than usual
  • System shutdown if the valve stays open

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€250–1,300
Time1–4 h

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

Parts involved

anode drain valve

Related codes

U356AU356DU356EU3569

References: patents.google.com, patents.google.com, patents.google.com.