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DTC codes / U35xx · Network communication / U356E

U356EAnode Drain Valve Heater Relay Control Circuit

The U356E code indicates that the powertrain control module (PCM) has detected a fault in the control circuit for the anode drain valve heater relay, which is part of the vehicle's evaporative emissions or fuel system. The computer monitors the circuit for expected voltage or current and sets this code when the signal is out of range, indicating an open, short, or excessive resistance in the wiring or relay.

SystemNetwork
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaNetwork communication

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) on the dashboard.
  • Often no symptoms besides the warning light, as the anode drain valve heater is a minor emissions component.
  • Possible rough idle or hesitation if the heater circuit fault affects fuel vapor flow.
  • A slight fuel odor may be noticed in rare cases if the valve fails to drain properly.
  • Reduced fuel economy in some instances due to improper vapor management.
  • Intermittent warning light if the circuit fault is temperature or vibration sensitive.

Common causes, most likely first

  1. Failed anode drain valve heater relay, which is the most common cause due to coil or contact wear.
  2. Open or shorted wiring in the control circuit between the PCM and the relay.
  3. Corroded or loose electrical connectors at the relay or PCM.
  4. Defective anode drain valve heater element causing excessive current draw.
  5. Faulty powertrain control module (PCM) driver circuit, though rare.
  6. Blown fuse or fusible link supplying power to the relay circuit.
  7. Water intrusion or physical damage to the wiring harness.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related diagnostic trouble codes (DTCs) in the PCM.
  2. Inspect the fuse and relay for the anode drain valve heater circuit, replacing any blown fuse or faulty relay.
  3. Perform a visual inspection of the wiring and connectors for damage, corrosion, or looseness.
  4. Use a digital multimeter to check for continuity and resistance in the control circuit between the PCM and relay.
  5. Test the anode drain valve heater element for resistance and compare to manufacturer specifications.
  6. Check for voltage and ground signals at the relay and PCM to confirm proper operation.
  7. If all circuits test good, consult factory service information for pinpoint tests and consider PCM replacement as a last resort.

Relay failures often mimic wiring faults

  • A failed anode drain valve heater relay is frequently the root cause, yet many technicians replace the valve itself without testing the relay first.
  • The code can be set by a simple blown fuse that also powers other circuits, so always check fuses before condemning expensive components.
  • Intermittent codes often result from poor connector pin tension or corrosion that only acts up under certain conditions, so wiggle-test wiring while monitoring live data.
  • This circuit is part of the evaporative emissions system on many vehicles, so a fault may not affect driveability but will prevent the EVAP monitor from running.
  • After repairs, clear the code and perform a drive cycle to verify the repair, as the PCM may need to see the heater circuit operate correctly before turning off the light.

Can I keep driving with U356E?

The vehicle is generally safe to drive with this code because it typically affects only an emissions-related heater circuit and does not impair engine operation. Avoid long-term driving without repair, as it may cause increased emissions and prevent the vehicle from passing an emissions inspection.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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