U3566 code meaning
Anode Inlet Pressure Sensor 1 Circuit
Network system Generic code U35xx codes Check engine light
What U3566 means
U3566 is set for an electrical fault at anode inlet pressure sensor 1, sitting between hydrogen injector and stack. A GM patent explains why this value is central: it closes the loop for the injector and also feeds anode valve control and the handling of hydrogen in the exhaust. A wrong value derails that loop; in GM's example the injector is held at full duty because a 200 kPa target never shows on a sensor stuck at 100 kPa. GM flags such a sensor when its readings vary by less than 6 kPa over a time window and then runs the anode open loop, about 50 kPa above cathode pressure. Hyundai checks its stack supply pressure sensor against recirculation blower speed and warns in the cluster. As a circuit code U3566 covers opens and shorts; no public source uses it. Expect a warning and reduced power.
U3566 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U3566
- Fuel cell system warning, MIL on
- Noticeably reduced power
- Rough or interrupted fuel cell start
Common causes of U3566
- Most likelyOpen, short or corrosion in wiring or connector of sensor 1 at the stack
- PossibleAnode inlet pressure sensor 1 faulty internally
- Less likelyShared 5 V supply or ground faulty (often with other sensor codes)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Anode inlet pressure sensor 1Sensor wiring
What each part of U3566 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 66 | The exact fault in that area. |
What to do next
- Note U3566 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 U3566
What does U3566 mean?
U3566 means "Anode Inlet Pressure Sensor 1 Circuit". U3566 is set for an electrical fault at anode inlet pressure sensor 1, sitting between hydrogen injector and stack. It is a generic code, so it means the same on every make.
Is it safe to drive with U3566?
Drive gently and only to a workshop. With U3566 the car can go into limp mode (reduced power) to protect itself.
Will U3566 fail an emissions test?
U3566 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 U3566 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U3566 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.