Powertrain, generic (extended)

P2A85 Alternative Fuel Pump B Compression Stroke Valve Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2A85 means the drive output for pump B's compression stroke valve reads too low for its commanded state. Typical are a control wire chafed through to the frame, which can keep the solenoid energised even when the controller wants it off, or a coil with shorted windings that draws excessive current. A valve stuck in the fill position leaves pump B's plunger parked at full extension; the pump stops delivering, and pressurised oil remains on its drive side. Caterpillar's six-element example can partly make up for this with the remaining elements, whereas a two-tank system loses the second tank's supply. No manufacturer publishes P2A85. Compare the measured coil resistance with that of an identical A or C valve.

Likely causes

Control wire of valve B chafed through to the frame
Coil of valve B with shorted windings
Output stage for valve B shorted

Symptoms

  • Warning lamp on
  • Pump B delivers nothing, reduced power or range

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

P2A83P2A84P2A86P2A81P2A89

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