Powertrain, generic (extended)

P2A86 Alternative Fuel Pump B Compression Stroke Valve Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2A86 is stored when pump B's compression stroke valve circuit shows a higher voltage than its state allows, pointing to an interrupted coil, a broken return wire where the valve is switched on the ground side, or a short to the supply. The valve then rests in its drain position: drive oil bypasses pump B and its plunger stays retracted. On a two-tank layout as in Westport's patent, the controller may keep drawing from the other tank, so the truck runs on while the second tank's LNG cannot be used and slowly warms up. Because the pump performs no strokes, its usual hydraulic pressure signature disappears, which helps to confirm the diagnosis. No manufacturer documents P2A86. Check the coil, the plug and the supply feed.

Likely causes

Open coil or broken wire at valve B
Control wire shorted to supply voltage
Corroded terminals in the valve B plug

Symptoms

  • Warning lamp on
  • One LNG tank is no longer emptied
  • Shorter range on gas

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–1,500
Time1–4 h

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

Parts involved

alt fuel pump b compression stroke valvewiring harnessafcm

Related codes

P2A83P2A84P2A85P2A82P2A8A

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