Network, generic (extended)

U354D Hydrogen Tank B Temperature Sensor 2 Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Moisture or damage at the underbody connector of tank B
Temperature sensor 2 of tank B failed
Harness chafed after underbody or tank work

Symptoms

  • Hydrogen system warning
  • Fuel gauge less accurate
  • Refuelling ends early

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–4,000
Time0.5–6 h

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

Parts involved

h2 tank b temp sensor 2sensor wiring

Related codes

U354CU354BU354F

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