U356EAnode Drain Valve Heater Relay Control Circuit
- Generic OBD-II code · Network
- How the car detects it
- U356E refers to the relay that powers the heater on the anode drain valve, more precisely to its coil drive from the fuel cell controller. Drain valves sit in the wettest corner of the hydrogen loop and can freeze shut after a cold night. Hyundai fits PTC heaters to its purge valves, fed by the battery and switched on when a start below freezing is detected; Parker Hannifin places a PTC element right at the seat of a fuel cell drain valve, and Hilite sells drain valves with built-in heating that still open at minus 40 °C. If the relay cannot be driven, the heater stays off, or stays on and drains the battery. In mild weather nothing may be noticeable; in frost an iced drain valve can delay or prevent the start. No maker documents U356E publicly, and its MIL handling is unknown.
- What you may notice
- Fuel cell warning message
- Delayed or failed start in frost
- Often no noticeable effect in warm weather
- Likely causes
- LikelyOpen, short or corrosion in the relay coil wiring or connector
- PossibleHeater relay faulty
- RareFuse or supply of the relay circuit missing
- RareRelay driver in the fuel cell control unit faulty
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.