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U355C Charge Air Cooler Outlet Temperature Sensor Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U355C reports a circuit fault on the temperature sensor behind the charge air cooler. Compression heats the air strongly: Honda gives about 120 °C at the compressor outlet, while the stack works at 80 to 90 °C, so the air is first brought down to roughly 60 to 75 °C. The sensor confirms this cooling before the air reaches the humidifier. In a Toyota patent it sits between intercooler and humidifier, and if the intercooler coolant pump fails, the controller slows the compressor to keep air temperature below a set limit; Nissan derives an upper pressure limit from the same reading. No maker documents U355C publicly. Without a valid temperature, humidifier and membrane lose their protection, so a warning and a careful cut in power should follow. Pressure here is U355A/U355B.

Likely causes

Open or short in wiring or connector of the temperature sensor
Temperature sensor (thermistor) faulty internally
Sensor ground or reference circuit faulty

Symptoms

  • Fuel cell system warning, MIL on
  • Power limited, especially under sustained high load
  • Compressor runs at reduced speed

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–600
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cac outlet temperature sensorsensor wiring

Related codes

U355AU355BU3559

References: patents.google.com, patents.google.com, patents.google.com.