U356C code meaning
Anode Header Drain Valve Control Circuit
Network system Generic code U35xx codes Check engine light
What U356C means
U356C covers the drive circuit of a second drain valve mounted directly on the anode exhaust header, the channel inside the stack that gathers the gas leaving every cell. GM lists three valves behind the stack: a bleed valve at the top of the anode sump, a drain valve at its bottom and this header valve, which empties into the cathode exhaust. Condensate pooling in the outlet header harms cell durability, above all when the car stands on a steep slope, and GM has also patented heating of these manifolds against ice. Older logic opened the header valve only at shutdown or on a tilt sensor signal; GM's newer scheme lets it serve a share of bleed requests, by default the fifth. If the drive is open or shorted, the water stays put. No maker documents U356C publicly; a warning and limited operation are likely. The sump drain circuit is U356A.
U356C 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 U356C
- Fuel cell system warning, MIL on
- Power limited, especially after parking on a slope
- Often no noticeable effect at first
Common causes of U356C
- Most likelyOpen, short or corrosion in wiring or connector of the header drain valve
- PossibleValve solenoid coil open or shorted
- Less likelyDriver stage of the fuel cell control unit faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Anode header drain valveValve wiring
What each part of U356C means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 6C | The exact fault in that area. |
What to do next
- Note U356C 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 U356C
What does U356C mean?
U356C means "Anode Header Drain Valve Control Circuit". U356C covers the drive circuit of a second drain valve mounted directly on the anode exhaust header, the channel inside the stack that gathers the gas leaving every cell. It is a generic code, so it means the same on every make.
Is it safe to drive with U356C?
Drive gently and only to a workshop. With U356C the car can go into limp mode (reduced power) to protect itself.
Will U356C fail an emissions test?
U356C 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 U356C to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U356C clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.