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DTC codes / P0Bxx · Hybrid propulsion / P0B06

P0B06Electric/Auxiliary Transmission Fluid Pump Motor Phase W Current

P0B06 is set when the transmission control module detects that the electrical current in phase W of the auxiliary transmission fluid pump motor is outside the expected range during operation or self-test. This pump maintains fluid pressure when the engine is stopped, so the fault often affects stop-start and hybrid driving modes rather than normal driving.

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

Symptoms you may notice

  • Illumination of the check engine light or service transmission warning
  • Often no symptoms besides the warning light, especially if the engine-driven pump still provides pressure
  • Harsh or delayed engagement when accelerating from a stop in vehicles that rely on the auxiliary pump
  • The vehicle may refuse to enter engine stop-start mode or may stall when coming to a stop
  • Reduced fuel economy due to the engine idling instead of shutting off
  • In rare cases, a no-move condition if the auxiliary pump is the sole pressure source

Common causes, most likely first

  1. Damaged or chafed wiring in the phase W circuit between the control module and the pump motor
  2. Corroded, loose, or water-intruded connector at the auxiliary pump or control module
  3. Failed auxiliary transmission fluid pump motor (open or shorted phase winding)
  4. Faulty auxiliary pump control module or internal driver for phase W
  5. Low or contaminated transmission fluid causing pump overheating and current draw changes
  6. Internal transmission mechanical issues that increase pump load

How to diagnose and fix it

  1. Verify battery voltage and condition, then clear the code and perform a road test to confirm it returns
  2. Inspect the auxiliary pump harness and connectors for chafing, corrosion, or loose pins, focusing on the phase W circuit
  3. Measure resistance of the phase W winding at the pump connector and compare with the other phases to detect an open or short
  4. Check for service bulletins and software updates for the transmission control module that address pump current monitoring
  5. If electrical checks are normal, perform the manufacturer's guided diagnostic for the auxiliary pump, which may include commandeering the pump with a scan tool
  6. Replace the auxiliary transmission fluid pump motor or control module as indicated by test results, following the service procedure
  7. After repair, clear codes and verify the auxiliary pump operates correctly during engine stop-start events

Auxiliary pump faults that fool technicians

  • A weak or failing 12-volt battery can cause the auxiliary pump to draw excessive current and set P0B06 without any fault in the pump itself.
  • Transmission fluid that is low or contaminated with debris can overwork the auxiliary pump and trigger a phase current code, so always check fluid condition first.
  • The code can be stored intermittently by a momentary voltage spike or a poor ground connection that only acts up under specific temperature or vibration conditions.
  • On some vehicles, the auxiliary pump only runs during engine stop-start events, so a fault may not appear during a conventional test drive without forcing those conditions.
  • A phase W current code does not always mean the pump motor is failing; the control module's internal current sensing circuit can drift and report false faults.

Can I keep driving with P0B06?

You can generally continue driving because the engine-driven pump provides normal hydraulic pressure, but avoid relying on engine stop-start features and have the fault diagnosed soon to prevent possible loss of pressure during auto-stop events.

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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