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DTC codes / P27xx · Transmission / P276A

P276AElectric/Auxiliary Transmission Fluid Pump B Motor Supply Voltage Circuit / Open

P276A indicates that the transmission control module (TCM) has detected an open circuit or supply voltage fault in the electrical path for the auxiliary transmission fluid pump motor, specifically on the B-side circuit. This pump is used in some automatic transmissions to maintain fluid pressure when the engine is stopped, such as during engine auto-stop events, and the TCM monitors the motor supply voltage to ensure the pump can operate when commanded.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) on the dashboard, often with no other noticeable symptoms.
  • The engine auto-stop feature may be disabled, causing the engine to remain running when it would normally shut off at a stop.
  • Harsh or delayed transmission shifts may occur if the auxiliary pump cannot maintain pressure during engine-off periods.
  • In some cases, the transmission may enter limp mode or fail to engage drive or reverse after an auto-stop event.
  • A stored diagnostic trouble code (DTC) P276A may be the only evidence, with no drivability complaints reported by the driver.

Common causes, most likely first

  1. An open circuit in the wiring harness or connector between the TCM and the auxiliary transmission fluid pump motor, often due to corrosion, chafing, or a loose pin.
  2. A failed auxiliary transmission fluid pump motor, such as a burned-out winding or internal open circuit.
  3. A blown fuse or faulty relay that supplies power to the auxiliary pump motor circuit.
  4. High resistance or damage at the pump motor electrical connector, including water intrusion or terminal fretting.
  5. A faulty TCM or power control module that fails to provide the correct supply voltage to the pump motor.
  6. Poor ground connection for the auxiliary pump motor circuit, leading to voltage drop under load.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related DTCs in the TCM and other modules to confirm the fault is isolated to the auxiliary pump supply circuit.
  2. Inspect the auxiliary pump motor fuse and relay, and test them for continuity and proper operation; replace any blown fuse or faulty relay.
  3. Visually inspect the wiring harness and connectors at the auxiliary pump motor and TCM for signs of damage, corrosion, or loose terminals; repair or replace as needed.
  4. Perform a voltage drop test on the supply circuit to the auxiliary pump motor while commanding the pump on with a scan tool, checking for excessive resistance.
  5. Measure resistance across the auxiliary pump motor terminals and compare to the manufacturer's specification to determine if the motor is open or shorted.
  6. If the motor tests bad, replace the auxiliary transmission fluid pump motor and clear the code, then verify the repair with a test drive that includes auto-stop events.
  7. If all circuits and components test good, suspect an internal TCM fault; follow the manufacturer's diagnostic flow for TCM replacement or reprogramming.

Don't overlook the simple supply circuit

  • A common oversight is replacing the auxiliary pump motor when the actual fault is a corroded connector or chafed wire that only shows an open circuit under vibration or temperature change.
  • The code can set intermittently due to a loose ground connection at the chassis, which may test fine when static but fail under load; always perform a loaded voltage drop test.
  • Some vehicles use the auxiliary pump only during auto-stop events, so a failed pump may not affect normal driving until the engine shuts off at a stop, leading to a no-start or delayed engagement condition.
  • A weak or failing battery can cause the TCM to log this code if supply voltage drops during cranking, so check battery health and charging system before condemning the pump.
  • After repairs, the TCM may require a relearn or adaptation reset for the auto-stop system to function correctly; clearing the code alone may not restore normal operation.

Can I keep driving with P276A?

You can generally continue driving, but be aware that the engine auto-stop feature may be disabled and transmission engagement after a stop could be delayed or harsh. Avoid relying on auto-stop functionality and have the fault diagnosed promptly to prevent potential transmission damage or a no-drive condition.

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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