U3556 code meaning
Hydrogen Tank C Valve Control Circuit
Network system Generic code U35xx codes Check engine light
What U3556 means
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.
U3556 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 8 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U3556
- Hydrogen system warning
- Range noticeably shorter after a full fill
Common causes of U3556
- Most likelyWiring or connector fault at the tank C valve
- PossibleValve coil open or shorted
- Less likelyDriver stage for valve C faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
H2 tank c valveValve wiring
What each part of U3556 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 56 | The exact fault in that area. |
What to do next
- Note U3556 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 U3556
What does U3556 mean?
U3556 means "Hydrogen Tank C Valve Control Circuit". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with U3556?
Drive gently and only to a workshop. With U3556 the car can go into limp mode (reduced power) to protect itself.
Will U3556 fail an emissions test?
U3556 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 U3556 to fix?
Difficulty: workshop only. A typical repair takes 1 to 8 hours of work. This is a job for a workshop.
Will U3556 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.