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DTC codes / P0Bxx · Hybrid propulsion / P0B0C

P0B0CElectric/Auxiliary Transmission Fluid Pump A Hydraulic Leakage

P0B0C indicates that the transmission control module has detected a hydraulic leakage condition in the electric or auxiliary transmission fluid pump circuit A. The computer monitors pump performance and pressure, and when the pump cannot maintain the commanded pressure due to an internal or external leak, it sets this code and may disable the auxiliary pump function.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light, often with no other symptoms
  • Harsh or delayed shifting, especially when the vehicle is cold or under load
  • Transmission slipping or inability to engage certain gears
  • Overheating of the transmission fluid due to poor circulation
  • Whining or groaning noise from the transmission area when the auxiliary pump runs
  • Limp mode or reduced power mode if the fault escalates

Common causes, most likely first

  1. External hydraulic leak from the auxiliary pump body, seals, or connected lines
  2. Internal leakage past the pump's seals or worn pump components
  3. Damaged or deteriorated O-rings and gaskets at the pump mounting flange
  4. Cracked or loose hydraulic lines or fittings leading to or from the pump
  5. Contaminated transmission fluid causing seal degradation and internal leakage
  6. Faulty pressure sensor or wiring providing false leakage indications
  7. Mechanical failure of the pump itself, such as a scored housing or worn gears

How to diagnose and fix it

  1. Verify transmission fluid level and condition; top off or replace fluid if contaminated
  2. Inspect the auxiliary pump and surrounding area for external fluid leaks and trace lines for cracks or loose fittings
  3. Check pump electrical connector and wiring for corrosion or damage, and confirm pump activation with a scan tool
  4. Perform a pressure test on the auxiliary pump circuit to confirm hydraulic leakage versus sensor error
  5. Remove and disassemble the auxiliary pump to inspect seals, O-rings, and internal components for wear or damage
  6. Replace faulty seals, gaskets, or the entire auxiliary pump assembly as needed
  7. Clear the code and road test to verify the repair and ensure no pending codes return

Hidden Causes of Auxiliary Pump Leak Codes

  • A common oversight is assuming the pump itself is faulty when the real leak is at a cracked line or loose fitting that only seeps under pressure.
  • Contaminated transmission fluid from neglected service intervals can cause seal swelling and internal leakage that mimics a failed pump.
  • Some vehicles set this code due to a faulty pressure sensor or wiring issue rather than an actual hydraulic leak, so always verify with a mechanical pressure gauge.
  • The auxiliary pump may only run under specific conditions such as engine start-stop events, so a leak might not be present during a static inspection.
  • After replacing the pump, air trapped in the hydraulic circuit can cause a repeat code until the system is properly bled and fluid level stabilized.

Can I keep driving with P0B0C?

Driving with P0B0C is generally not recommended because a hydraulic leak can lead to transmission overheating and internal damage. If the vehicle must be moved, keep the distance short and avoid heavy loads or aggressive acceleration, and monitor fluid level closely.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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