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DTC codes / U35xx · Network communication / U354F

U354FHydrogen Tank C Temperature Sensor 2 Circuit

The U354F code indicates that the powertrain control module (PCM) has detected an abnormal condition in the temperature sensor circuit for the second sensor on the hydrogen tank C. This sensor is used to monitor the temperature of the hydrogen storage system, and the circuit's voltage or resistance is outside the expected range, triggering the warning.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
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 vehicle may continue to operate normally.
  • Reduced power or limited operation if the PCM enters a fail-safe mode to protect the hydrogen system.
  • Inaccurate or erratic temperature readings on the instrument cluster, if equipped with a hydrogen temperature gauge.
  • Possible difficulty refueling if the system relies on temperature data to control the refueling process.
  • In rare cases, the vehicle may refuse to start or may shut down unexpectedly if the fault is interpreted as critical.

Common causes, most likely first

  1. Faulty temperature sensor 2 on hydrogen tank C, such as an open or shorted internal element.
  2. Damaged or corroded wiring harness or connector at the sensor or PCM.
  3. Poor electrical connection due to loose pins or water intrusion in the connector.
  4. Open or short circuit in the sensor signal or ground circuit.
  5. PCM internal fault affecting the sensor input circuit.
  6. Aftermarket accessories or modifications that interfere with the sensor wiring.

How to diagnose and fix it

  1. Connect a scan tool and verify the U354F code is current, then check for any related codes and freeze-frame data.
  2. Visually inspect the sensor, connector, and wiring for damage, corrosion, or loose connections; repair as needed.
  3. Measure the resistance of the temperature sensor with a multimeter and compare to the manufacturer's specification for the ambient temperature.
  4. Check the sensor signal circuit for an open or short to ground or voltage using a multimeter and wiring diagram.
  5. Check the sensor ground circuit for continuity to the PCM ground.
  6. If the circuit tests good, substitute a known-good sensor and clear the code to see if it returns.
  7. If the code persists after sensor replacement, diagnose the PCM and its programming, and replace or reprogram as required.

Hydrogen Sensor Circuit Diagnostics

  • A common mistake is to replace the sensor without checking the wiring, as chafed or corroded harnesses often cause this code.
  • The code can set intermittently due to vibration or temperature extremes, so a wiggle test of the harness while monitoring sensor data is valuable.
  • On some vehicles, a low 12-volt battery or poor ground can cause false sensor codes, so always verify battery condition and grounds first.
  • The U354F code may be accompanied by other hydrogen system codes, and addressing those first can resolve the U354F as a secondary fault.
  • This code does not always indicate a failed sensor; it can be triggered by a PCM software glitch that requires a reflash.

Can I keep driving with U354F?

If the vehicle drives normally and the only sign is the warning light, you can drive to a workshop for diagnosis, but avoid long trips or heavy loads. If the vehicle enters limp mode or shows other warnings, stop driving and seek professional assistance, as the hydrogen system may be compromised.

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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