Powertrain, generic · Hybrid propulsion

P0B0B Electric/Auxiliary Transmission Fluid Pump A Motor Supply Voltage Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0B0B reports a supply voltage at the motor of auxiliary pump A that is above the expected range. Subaru documents it on the 2014-15 XV Crosstrek Hybrid (bulletin 16-94-15R), together with P172A: a leaking O-ring at the electric oil pump relief valve can let CVT fluid into the pump motor. The check removes the three U, V and W cables at the oil pump inverter and reads AC voltage across them with the engine held at 1800 rpm in Park; 0.5 V or more means the drive motor and case assembly with the damaged seal must be replaced, less means the cause lies elsewhere. Subaru adds that P0C79, drive motor inverter voltage too high, appears only together with these codes and does not mean the inverter is faulty. P0B09 and P0B0A are the open and low variants.

Likely causes

CVT fluid entering the pump motor via a leaking relief valve O-ring (Subaru XV Crosstrek Hybrid)
Supply circuit shorted to a higher voltage source
Oil pump inverter or its voltage sensing faulty

Symptoms

  • Warning lamp on, hybrid or CVT function restricted
  • Possibly P0C79 stored at the same time

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–6,000
Time1–12 h

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

Parts involved

aux trans pump a motorwiring harnesstcm

Related codes

P0B09P0B0AP0B0CP0C79

References: static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.