U354A code meaning
Hydrogen Tank A Temperature Sensor 1 Circuit
Network system Generic code U35xx codes Check engine light
What U354A means
U354A reports an electrical fault on the first temperature sensor of hydrogen tank A. Tank sensors matter most while refuelling: compression heats the gas, and FMVSS 308 slows the pressure ramp once the gas inside passes 85 °C; on the Mirai the tank temperature is passed to the dispenser by infrared. No maker publishes U354A, but Honda shows how such faults appear on the 2017 Clarity Fuel Cell under its own codes P1F76 (main tank) and P1F77 (sub tank): they set during fuelling, and because the sensor sits inside the tank, the first remedy in Tech Line article ATS 170903 was a new tank. Bulletin 19-001 later blamed many cases on outdated software in the fuel cell communication unit. Sensor 2 of the same tank is U354B.
U354A at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor0.3 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U354A
- Code sets while refuelling
- Hydrogen system warning
- Refuelling slower or ends before the tank is full
Common causes of U354A
- PossibleOutdated software in the unit that evaluates the tank sensors
- PossibleTemperature sensor inside the tank failed (often only as tank assembly)
- PossibleOpen or short in the sensor wiring or connector at the tank
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
H2 tank a temp sensor 1Sensor wiring
What each part of U354A means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 4A | The exact fault in that area. |
What to do next
- Note U354A 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 U354A
What does U354A mean?
U354A means "Hydrogen Tank A Temperature Sensor 1 Circuit". U354A reports an electrical fault on the first temperature sensor of hydrogen tank A. It is a generic code, so it means the same on every make.
Is it safe to drive with U354A?
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 U354A fail an emissions test?
U354A 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 U354A to fix?
Difficulty: workshop only. A typical repair takes 0.3 to 6 hours of work. This is a job for a workshop.
Will U354A clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.