Powertrain, generic (extended)

P2A91 Alternative Fuel Tank Select Valve A Control Circuit/Open

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

A tank select valve decides which storage vessel feeds the fuel system. That sets it apart from a tank shutoff valve (P224C, P2A22 and onward), which simply opens or isolates one cylinder, and from the hydraulic fuel pump select valve (P2A70 and onward), which routes drive oil to a pump. Westport's patent US8726785B2 shows the idea with two LNG vessels and one external pump, where an insulated valve links the pump to either vessel. P2A91 means the control circuit of select valve A is open or otherwise faulty, so the valve stays in its rest position. Fuel is then drawn only from the vessel reached in that position and the rest may become unusable. No manufacturer documents P2A91 publicly; CARB requires output circuits to be checked for continuity.

Likely causes

Loose connector or broken wire to select valve A

Burnt-out solenoid coil of valve A

Faulty output stage in the alternative fuel module

Symptoms

Malfunction lamp on
Only one tank is used, range noticeably shorter
Fuel gauge shows content left although the engine runs short of gas

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–1,200

Time1–4 h

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

Parts involved

alt fuel tank select valve awiring harnessafcm

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