U356E
Anode Drain Valve Heater Relay Control Circuit.
- Generic
- Network
- Generic code
- Medium severity
How this code is built
- U
- SystemNetwork
- 3
- Defined bySAE, the same on every car
- 5
- AreaNetwork area 5
- 6E
- FaultThe specific fault in that area
What it means
U356E refers to a fault in the control circuit of the relay that powers the anode drain valve heater, a part of the fuel cell system on hydrogen vehicles. The control unit that commands the relay saw a circuit or communication state that did not match what it expected, such as an open circuit, a short, or no valid feedback. The exact relay, control unit and set conditions depend on the model, so check the manufacturer's data.
Symptoms
- Fuel cell or powertrain warning light on
- Reduced power or the vehicle limiting performance
- Difficulty starting or a fuel cell system start-up failure in cold weather
- Fuel cell system shutting down or refusing to ready
- Other fault codes stored in the fuel cell or hydrogen system control units
Possible causes
- Wiring fault in the heater relay control circuit (open circuit, short to earth or short to supply)likely
- Corroded, loose or damaged connector at the relay or control unitlikely
- Faulty heater relay, either failed internally or stuckpossible
- Low or unstable supply voltage or poor earth to the relay or control unitpossible
- Faulty anode drain valve heater element or its wiring causing a related circuit errorpossible
- Internal fault in the controlling module or an outdated software calibration known to affect this circuitrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting the ambient temperature and system state when the code set, and check for related codes in other modules.
- Look up the manufacturer's procedure for this model, as the layout and safety requirements for the fuel cell system vary. Only a technician trained in high-voltage and hydrogen systems should work on the system.
- Visually inspect the relay, its connector, and the wiring to the control unit for chafing, water ingress, corrosion and heat damage.
- Check the supply fuses and measure the relay supply voltage and earth under load, comparing the readings with the specification.
- Test the relay coil resistance and the relay's operation, then swap in a known good part only if the manufacturer permits it.
- Check the control circuit for continuity, short to earth and short to supply with the connectors disconnected, following the wiring diagram.
- Check the drain valve heater element resistance and its wiring against the specification.
- Check for software updates or technical bulletins relating to this code on the vehicle in question.
How to fix
- Repair or replace damaged wiring in the relay control circuit and secure any loose connections.
- Clean or replace corroded or damaged connectors and terminals, and restore any seals.
- Replace the faulty heater relay with a correct specification part.
- Repair the power supply or earth fault, and replace any blown fuse once the cause is found.
- Replace the faulty drain valve heater or its harness if testing shows it is defective.
- Update the control unit software or replace the module only if testing and the manufacturer's information confirm that this is the cause.
Can I keep driving?
The vehicle can often be driven for a short time, but get it checked soon, as a heater that does not work can let the drain valve freeze in cold weather and affect the fuel cell system. If the vehicle shows a stop warning, smells of gas, or goes into limited power, stop safely and seek specialist help.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.