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U355E Expander Inlet Pressure Sensor 2 Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U355E names a circuit fault on pressure sensor 2 at the expander inlet. Conditions there are harsh: cathode exhaust carries the product water of the stack, and Volkswagen notes in a turbine patent that the pressure drop inside the turbine makes water condense even behind a droplet separator, eroding the blades. A Hannover study on fuel cell turbines likewise asks for robustness against droplets and lets the turbine set the cathode operating pressure. Ford describes how wet pressure sensors in a fuel cell can freeze and give no or false signals at a cold start. A second sensor lets the controller spot such a reading. No maker documents U355E publicly. A failure of sensor 2 alone mainly removes this cross-check; together with U355D the expander control is blind and power is likely limited.

Likely causes

Wiring or connector of sensor 2 corroded by exhaust moisture, open or shorted
Water frozen in the sensor port at cold start
Expander inlet pressure sensor 2 faulty internally

Symptoms

  • Fuel cell system warning, MIL on
  • Fault appears mainly after cold starts
  • Reduced power if sensor 1 is affected as well

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–800
Time0.5–3 h

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

Parts involved

expander inlet pressure sensor 2sensor wiring

Related codes

U355DU355FU3560U3562

References: patents.google.com, gpps.global, patents.google.com.