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U3563 Cathode Bypass Valve Position Sensor Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3563 means the position sensor on the cathode bypass valve delivers no usable signal because of a broken wire, a short or a voltage outside its window. Toyota's patent mounts such a valve body position sensor right at the bypass valve, with pressure sensors before and after it; the angle tells the controller how the compressor air is really being split between stack and bypass. A Hydrogenics patent likewise fits angle sensors to the throttle-type valves of its stack. No public manufacturer source names U3563. Without the feedback, the controller has to infer the valve state indirectly, for example from compressor outlet pressure or stack current as Toyota describes, and will usually restrict operation. Drive faults of the valve are U3561, a mechanically misbehaving valve U3562.

Likely causes

Open, short or moisture in the position sensor wiring or connector
Position sensor in the valve unit faulty
Shared 5 V supply or ground faulty (often with other sensor codes)

Symptoms

  • Fuel cell system warning, MIL on
  • Reduced power, especially at low load

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 valve position sensorsensor wiring

Related codes

U3561U3562U3560U355F

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