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DTC codes / P0Cxx · Hybrid propulsion / P0C27

P0C27Electric/Auxiliary Transmission Fluid Pump A Motor Current Low

P0C27 means the transmission control module (TCM) commanded the electric auxiliary transmission fluid pump on circuit A to run, but the current flowing through the pump motor stayed below the expected threshold. The computer sees an open or high-resistance path in the pump motor circuit, so the pump is not drawing the current it should.

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

Symptoms you may notice

  • Illumination of the check engine light or transmission warning lamp, often with no other symptoms besides the warning light
  • Transmission may enter limp mode or default to a fixed gear when the auxiliary pump is needed for fluid pressure
  • Harsh or delayed shifting, especially after an auto start-stop event or while the engine is off in a hybrid
  • Loss of drive or reduced power if the auxiliary pump is responsible for maintaining pressure during engine shutdown
  • A stored pending or confirmed P0C27 code with possible related pump circuit codes in the TCM memory

Common causes, most likely first

  1. Open or high-resistance wiring in the pump motor power or ground circuit, including a broken wire or corroded connector terminal
  2. Failed electric auxiliary transmission fluid pump motor, such as an open winding or worn brushes
  3. Blown fuse or tripped relay dedicated to the auxiliary transmission fluid pump circuit
  4. Poor connection at the pump harness connector, the TCM connector, or a body ground shared with the pump circuit
  5. Internal fault in the transmission control module (TCM) driver circuit for the pump, though this is less common
  6. Low or contaminated transmission fluid that causes the pump to cavitate or run dry, indirectly affecting current draw

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data for P0C27, then clear the code and verify whether it returns under the same conditions
  2. Inspect the auxiliary pump fuse, relay, and wiring harness for obvious damage, corrosion, or loose connectors before any parts replacement
  3. Measure resistance across the pump motor terminals and compare with the manufacturer's specification to check for an open winding
  4. Back-probe the pump power and ground circuits at the pump connector while commanding the pump on with a scan tool, looking for voltage drop or missing current
  5. Perform a voltage drop test on the ground side of the pump circuit to rule out a bad chassis ground or connector terminal
  6. If the circuit tests good, substitute a known-good pump or use a current clamp to confirm actual pump current draw against the TCM's expected value
  7. After repair, clear codes, run the auxiliary pump activation test, and road-test the vehicle through several auto start-stop cycles to confirm the code does not reset

What the pump current test really shows

  • A low-current code often comes from a simple open circuit, such as a chafed wire or a corroded pin, rather than a failed pump motor, so always check the harness before condemning the pump.
  • The auxiliary pump may only run during engine auto start-stop events or in hybrid electric mode, so a P0C27 can stay pending for days and only set when those conditions are met.
  • A weak or failing battery can cause the TCM to log a low-current pump code if system voltage drops during the pump command, so load-test the battery before deeper circuit diagnosis.
  • Some vehicles use a pulse-width-modulated (PWM) signal to control pump speed, and a stuck-open driver in the TCM can mimic a bad pump motor on a current test.
  • Transmission fluid level and condition matter: a pump that is starved of fluid can draw less current than expected and set this code without any electrical fault at all.

Can I keep driving with P0C27?

You can usually drive the vehicle to a repair shop, but avoid relying on auto start-stop or hybrid electric-only operation because the auxiliary pump may not maintain transmission pressure. If the transmission enters limp mode or driveability worsens, stop driving and have it towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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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