U3555 code meaning
Hydrogen Tank B Valve Performance
Network system Generic code U35xx codes Check engine light
What U3555 means
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.
U3555 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor2 to 10 hours
- Clears after repairAfter a drive cycle
Symptoms of U3555
- Hydrogen system warning, sometimes after parking
- Range lower than expected
Common causes of U3555
- PossibleTank B valve seat leaking when closed
- PossibleValve not opening mechanically
- Less likelyManual tank valve not reopened after service
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
H2 tank b valve
What each part of U3555 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 55 | The exact fault in that area. |
What to do next
- Note U3555 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 U3555
What does U3555 mean?
U3555 means "Hydrogen Tank B Valve Performance". U3555 reports that the valve on tank B does not behave as expected although its circuit tests good. It is a generic code, so it means the same on every make.
Is it safe to drive with U3555?
Drive gently and only to a workshop. With U3555 the car can go into limp mode (reduced power) to protect itself.
Will U3555 fail an emissions test?
U3555 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 U3555 to fix?
Difficulty: workshop only. A typical repair takes 2 to 10 hours of work. This is a job for a workshop.
Will U3555 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.