U3559 code meaning
Air Inlet Pressure Sensor Circuit
Network system Generic code U35xx codes Check engine light
What U3559 means
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.
U3559 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U3559
- Fuel cell system warning, MIL on
- Reduced power, especially under high load or at altitude
- Unusual compressor noise
Common causes of U3559
- Most likelyConnector or wiring at the air filter housing wet, corroded or damaged
- PossibleInlet pressure sensor faulty internally
- Less likely5 V supply or ground of the sensor missing
- Less likelyFuel cell control unit faulty or needing a software update
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Air inlet pressure sensorSensor wiring
What each part of U3559 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 59 | The exact fault in that area. |
What to do next
- Note U3559 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U3559
What does U3559 mean?
U3559 means "Air Inlet Pressure Sensor Circuit". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with U3559?
Drive gently and only to a workshop. With U3559 the car can go into limp mode (reduced power) to protect itself.
Will U3559 fail an emissions test?
U3559 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U3559 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will U3559 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.