Powertrain, generic (extended)

P2A55 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

A second vaporizer appears where one heat exchanger cannot supply enough gas, for instance on large or heavy-duty engines. On LNG trucks the job is harder still: Westport's patent CA2862664C starts from liquid near −160 °C, heats it with engine coolant and places a gas temperature sensor downstream of the exchanger to choose how the coolant flows. P2A55 reports a circuit fault of the outlet sensor on vaporizer B that the module cannot sort into low or high. For heavy-duty alternative fuel engines from model year 2018, CARB section 1971.1 lets each maker submit its own monitoring plan, which helps explain why public code lists are scarce; none documents P2A55. The intact sensor on vaporizer A helps as a comparison while tracing plug and harness of B.

Likely causes

Plug or harness of the vaporizer B sensor damaged

Vaporizer B outlet sensor failed

Fault in the sensor input of the control module

Symptoms

Check engine light, depending on calibration
Reduced power or gas mode limited
Fall-back to the second fuel on dual-fuel engines

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€100–600

Time0.5–2.5 h

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

Parts involved

alt fuel vaporizer b outlet temp sensorwiring harnessafcm

References: law.cornell.edu, patents.google.com, law.cornell.edu.