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U356A Anode Drain Valve Control Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U356A concerns the electrical drive of the solenoid sitting under the anode water trap, which lets condensate leave the hydrogen loop. Hyundai opens it when a level sensor reports a full trap and closes it at a low mark so no hydrogen follows; if that sensor fails, the valve is closed as soon as anode pressure falls faster than a set rate. GM also gives the drain valve an emergency role: after an injector sticks open, hydrogen may be let out through it until the concentration in the exhaust reaches a limit. A broken or shorted drive circuit takes away both jobs. No maker documents U356A publicly. Since water keeps collecting in the anode, a warning and reduced or interrupted operation are plausible. The valve's mechanical state is U356B, the header drain circuit U356C.

Likely causes

Open, short or corrosion in wiring or connector of the drain valve
Drain valve solenoid coil open or shorted
Driver stage of the fuel cell control unit faulty

Symptoms

  • Fuel cell system warning, MIL on
  • Reduced power after some driving time
  • Fuel cell system shuts down

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–1,000
Time0.5–3 h

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

Parts involved

anode drain valvevalve wiring

Related codes

U356BU356CU356EU3568

References: patents.google.com, patents.google.com.