U356E: Anode Drain Valve Heater Relay Control Circuit

What it means

Anode Drain Valve Heater Relay Control Circuit: the control circuit has an electrical fault.

At a glance

• Usually lights the warning light of the system that lost communication

How it works

The anode drain valve heater relay switches power to the heater associated with the anode drain valve. This code indicates an electrical fault in the relay control circuit, so the module may be unable to switch the heater as commanded.

Common causes

Most likely first.

1. Heater relay failed
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Save freeze-frame data and scan all modules for relay-control and network communication faults.
2. Check scan-tool data or an available actuator test to see whether the anode drain valve heater relay is being commanded.
3. Inspect the relay, its connector, and the associated wiring for corrosion, loose pins, or heat damage.
4. Test the relay control circuit, power, and ground against the manufacturer's wiring information, and check relay operation as specified by the manufacturer.
5. If other devices also show communication faults, investigate CAN wiring and gateway routing before replacing the relay.

Common fixes

• Reconnect the heater relay or repair damaged control wiring.
• Repair a confirmed power or ground fault in the relay circuit.
• Replace the anode drain valve heater relay if its control circuit is sound but the relay fails its specified test.
• Repair a confirmed CAN wiring or gateway routing fault.
• Replace a CAN terminating resistor only if testing confirms it is out of specification.

Can I keep driving?

If cold conditions bring on fuel-cell warnings, reduced power, or shutdown, stop when safe and arrange diagnosis; the drain-valve heater may not operate and the drain system may be affected. Avoid relying on the vehicle until the fault is checked if these symptoms occur.