Powertrain, generic (extended)

P2A74 Alternative Fuel Hydraulic Fuel Pump Select Valve Control Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2A74 covers brief, recurring faults in the select valve control circuit that clear before a firm low or high verdict. On LNG trucks the valve usually sits near the tank-mounted pump and hydraulic lines, where frame flex, road spray and very cold surfaces around the cryogenic tank stress connectors and insulation. A valve that drops out for a moment can cut hydraulic flow to the working pump mid-stroke; because Westport's control logic recognises the stroke end from pressure changes, such dropouts may also upset pump timing. Typical finds are loose terminals, corroded pins and wiring chafed along the frame rail. No manufacturer publishes P2A74. Wiggle the harness while watching the output status, and check the plug for moisture.

Likely causes

Loose terminal in the select valve connector
Moisture or ice in the connector near the cryogenic tank
Harness chafed along the frame rail with intermittent contact

Symptoms

  • Check engine light on, may go out again
  • Brief hesitation or pressure dips in gas mode
  • Irregular tank changeover

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–900
Time1–4 h

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

Parts involved

alt fuel hyd pump select valvewiring harnessafcm

Related codes

P2A70P2A71P2A72P2A73

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