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U3559 Air Inlet Pressure Sensor Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3559 flags a wiring or signal fault on the first pressure sensor of the air supply that feeds the stack, located behind the air filter and ahead of the electric compressor. Its reading is the suction pressure of the compressor: in a Toyota patent the delivery pressure is divided by it to place the operating point on the compressor map and keep clear of the surge line, and Nissan derives the compressor inlet pressure the same way from a barometric sensor. Altitude and a clogged filter also show up here. No maker documents U3559 publicly. Without the value the controller has to work with a substitute, the margin to surge shrinks, and output is likely held back. Honda's Clarity shows that air supply faults in such cars light the MIL. Sensors further downstream report as U355A and U355B.

Likely causes

Connector or wiring at the air filter housing wet, corroded or damaged
Inlet pressure sensor faulty internally
5 V supply or ground of the sensor missing
Fuel cell control unit faulty or needing a software update

Symptoms

  • Fuel cell system warning, MIL on
  • Reduced power, especially under high load or at altitude
  • Unusual compressor noise

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–700
Time0.5–2.5 h

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

Parts involved

air inlet pressure sensorsensor wiring

Related codes

U355AU355BU355CU3561

References: patents.google.com, patents.google.com, static.nhtsa.gov.