U3559Air Inlet Pressure Sensor Circuit
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Fuel cell system warning, MIL on
- Reduced power, especially under high load or at altitude
- Unusual compressor noise
- Likely causes
- LikelyConnector or wiring at the air filter housing wet, corroded or damaged
- PossibleInlet pressure sensor faulty internally
- Rare5 V supply or ground of the sensor missing
- RareFuel cell control unit faulty or needing a software update
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €100 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.