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U3555 Hydrogen Tank B Valve Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

U3555 reports that the valve on tank B does not behave as expected although its circuit tests good. Leakage through the closed valve is one form. Hyundai patented a check for it while the car is parked: at wake-ups, hydrogen left in the supply line is fed into the stack with the tank valves shut, so the high-pressure reading should fall slightly; if it stays the same at each wake-up, the tank is feeding gas past the seal. The opposite is a valve that will not open. On the Nexo, venting for service closes the manual valve on each tank with a hex key, and a manual valve left shut afterwards would look like a stuck valve. No maker documents U3555. U3552 and U3558 are the siblings for A and C.

Likely causes

Tank B valve seat leaking when closed
Valve not opening mechanically
Manual tank valve not reopened after service

Symptoms

  • Hydrogen system warning, sometimes after parking
  • Range lower than expected

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€500–6,000
Time2–10 h

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

Parts involved

h2 tank b valve

Related codes

U3553U3554U3552U3558

References: patents.google.com, static.nhtsa.gov.