01 This Is Why Your Car Vibrates at High Speeds • 02 Don't Get Stranded! Warning Signs Your Hybrid Battery Needs… • 03 Experts Reveal Why Saying One Wrong Phrase At A Dealership … • 04 Mechanics Admit They're Surprised How Many Owners Don't Kno… • 05 The Secret ECU Behavior That Protects Your Engine Without W… • 06 Trucks of All Trades: Understanding the World of Trucks and… • 07 This One Oil Filter Mistake Could Be Silently Destroying Yo… • 08 Why Cars That Take Longer To Start In The Morning Are Often… • 09 Understanding Gear Ratios: How Transmissions Impact Perform… • 10 B1075 – Climate Control System Fault: Temperature Regulatio… •

DTC codes / P0Axx · Hybrid propulsion / P0A05

P0A05Motor Electronics Coolant Pump Control Circuit/Open

P0A05 indicates that the powertrain control module (PCM) has detected an open circuit or loss of continuity in the control circuit for the motor electronics coolant pump, which is the electric pump that circulates coolant through the inverter and motor electronics on hybrid and electric vehicles. The PCM commands the pump on and monitors the circuit for expected voltage or current feedback, and it sets this code when the circuit remains open or the feedback is missing.

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

Symptoms you may notice

  • Illumination of the check engine light or service vehicle soon message, often with no other noticeable symptoms
  • Reduced power or limp mode as the vehicle protects the motor electronics from overheating
  • Overheating warning or shutdown of the hybrid/EV system after extended driving
  • Audible absence of the electric coolant pump running when the ignition is on or the vehicle is started
  • Intermittent warning light that appears after the vehicle warms up or during certain driving conditions

Common causes, most likely first

  1. Failed electric coolant pump motor (open winding or seized pump)
  2. Damaged or disconnected wiring harness to the coolant pump, including chafed or corroded connectors
  3. Blown fuse or faulty relay supplying power to the coolant pump control circuit
  4. Open circuit in the control wire between the PCM and the coolant pump
  5. Poor ground connection for the coolant pump circuit
  6. Faulty PCM driver for the coolant pump control circuit (rare)

How to diagnose and fix it

  1. Verify the coolant pump fuse and relay, replacing any blown fuse or faulty relay as needed
  2. Inspect the coolant pump electrical connector and harness for corrosion, damage, or loose pins
  3. Measure resistance of the coolant pump motor windings and compare to specification
  4. Check for battery voltage and ground at the pump connector with the key on and the pump commanded on
  5. Perform a continuity test on the control circuit between the PCM and the pump connector
  6. Command the coolant pump on with a scan tool and listen for pump operation or check for current draw
  7. If all electrical checks pass, replace the coolant pump and clear the code

What the coolant pump circuit test reveals

  • A seized coolant pump can blow the fuse and set P0A05, so always check for a mechanically stuck pump before replacing electrical parts.
  • The PCM may set this code only after a commanded pump-on test fails, so the pump might run intermittently and still trigger the code.
  • Corrosion inside the pump connector is a common cause that is easily overlooked when the harness looks fine from the outside.
  • On some vehicles, a low coolant level or air pocket can cause the pump to overheat and fail electrically, leading to this code.
  • The code does not always mean the pump is dead; a wiring open or a bad ground can produce the same symptom and code.

Can I keep driving with P0A05?

Do not continue driving with this code because the motor electronics coolant pump may not be running, which can cause overheating and expensive damage to the inverter or motor. Have the vehicle towed or drive only a very short distance to a repair shop if absolutely necessary.

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.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage