U356AAnode Drain Valve Control Circuit
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Fuel cell system warning, MIL on
- Reduced power after some driving time
- Fuel cell system shuts down
- Likely causes
- LikelyOpen, short or corrosion in wiring or connector of the drain valve
- PossibleDrain valve solenoid coil open or shorted
- RareDriver stage of the fuel cell control unit faulty
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €150 – €1,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.