Network, generic (extended)

U3561 Cathode Bypass Valve Control Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3561 points to a break, a short or an output stage fault in the actuator circuit of the cathode bypass valve. This valve lets part of the compressor delivery skip the stack and flow straight into the exhaust. Nissan gives two reasons: keeping the compressor clear of surge when the stack needs little air, and putting enough air into the exhaust to dilute the hydrogen released when the anode is purged. Because opening the bypass lowers stack pressure, Nissan closes the pressure control valve a little further at the same moment. Toyota uses a three-way valve that can send the entire flow into the bypass when air pressure has to be dumped. No public maker document lists U3561. If the valve cannot be driven, a fuel cell warning is likely, along with limited power and possibly no start. Its mechanical behaviour is judged under U3562.

Likely causes

Open, short or corrosion in wiring or connector of the bypass valve
Bypass valve motor or actuator faulty
Driver stage of the fuel cell control unit faulty

Symptoms

  • Fuel cell system warning, MIL on
  • Reduced power, compressor speed fluctuating at low load
  • Fuel cell system does not start

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–1,200
Time0.5–3 h

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

Parts involved

cathode bypass valvevalve wiring

Related codes

U3562U3563U355FU3559

References: patents.google.com, patents.google.com.