U354D code meaning
Hydrogen Tank B Temperature Sensor 2 Circuit
Network system Generic code U35xx codes Check engine light
What U354D means
U354D marks an electrical fault on the second temperature sensor of tank B. Apart from fill control, tank temperature is needed to convert pressure into fuel quantity, because cold gas at a given pressure holds more hydrogen than warm gas. Sensors and wiring sit at the tank under the floor, often inside the on-tank valve. Hyundai's venting bulletin 20-FL-008H-1 for the Nexo has the underbody covers removed to reach the tank valves, requires tank pressure below 500 psi before work on hydrogen parts and full venting before welding or open flame within 18 inches. A sensor fault on the tank can therefore become a job involving defuelling. No maker publishes U354D. Its partner on the same tank is U354C.
U354D at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor0.5 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U354D
- Hydrogen system warning
- Fuel gauge less accurate
- Refuelling ends early
Common causes of U354D
- Most likelyMoisture or damage at the underbody connector of tank B
- PossibleTemperature sensor 2 of tank B failed
- Less likelyHarness chafed after underbody or tank work
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
H2 tank b temp sensor 2Sensor wiring
What each part of U354D means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 4D | The exact fault in that area. |
What to do next
- Note U354D 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 U354D
What does U354D mean?
U354D means "Hydrogen Tank B Temperature Sensor 2 Circuit". U354D marks an electrical fault on the second temperature sensor of tank B. It is a generic code, so it means the same on every make.
Is it safe to drive with U354D?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U354D fail an emissions test?
U354D 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 U354D to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 6 hours of work. This is a job for a workshop.
Will U354D clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.