P0A75 means the Hybrid/EV Control ECU has detected that **Motor Electronics Coolant Pump “A” is stuck OFF**. This electric pump circulates coolant through the inverter and power electronics to keep temperatures under control. When it fails to turn on, coolant flow stops and the inverter overheats quickly. You may notice reduced hybrid power, loud cooling fans, warning lights, or the vehicle refusing READY mode. Because overheating can damage expensive components, this code should be taken seriously. This guide explains P0A75 clearly—what it means, why it happens, and how to diagnose and fix it properly.
What Does P0A75 Mean?
P0A75 triggers when the ECU commands Motor Electronics Coolant Pump “A” to activate, but the expected electrical response or coolant flow does not occur. The ECU monitors pump status through current draw, voltage feedback, and temperature trends. If the pump fails to turn on, draws zero current, or does not create expected coolant temperature changes, the ECU assumes it is stuck OFF.
Because the inverter relies on active cooling even at low loads, a stuck pump can cause rapid temperature spikes. The hybrid system often enters limp mode or disables EV operation to protect the electronics.
Quick Reference
- OBD-II Family: P-Code (Hybrid Cooling System)
- Scope: Generic
- System: Inverter / Motor Electronics Cooling
- Difficulty Level: Moderate
- Estimated Repair Cost: €120–€450
- Last Updated: 2025-11-24
Real-World Example / Field Notes
We’ve seen P0A75 on Toyota Prius and Camry hybrids, Hyundai Ioniq and Kona Hybrid, Kia Niro, Ford Fusion Hybrid, and GM Voltec systems. One Prius repeatedly overheated on the highway because the inverter coolant pump seized internally—yet worked intermittently during cold engine bay tests, making diagnosis tricky. A Kia Niro Hybrid set P0A75 after a coolant flush because an air pocket prevented the pump from priming, causing the ECU to detect zero flow. In another case, a Ford hybrid had a corroded pump connector that intermittently cut power to the pump. Each case highlights the importance of checking both electrical supply and coolant flow.
Symptoms of P0A75
- Hybrid/EV warning lights: Often triggered immediately after startup.
- Loss of EV mode: The system avoids loading the inverter.
- Limp mode: Power decreased to reduce heat generation.
- Inverter overheating: Temperature increases rapidly.
- No coolant movement: Reservoir shows no turbulence.
- Cooling fans running loudly: System compensates for poor coolant flow.
- Vehicle shutting down (severe): READY mode may be blocked.
Common Causes of P0A75
Most Common Causes
- Failed coolant pump “A” (internal electronic or mechanical failure).
- Seized pump impeller preventing startup.
- Corroded, loose, or damaged pump connector.
- Air pockets preventing coolant flow after service.
- Open circuit in pump power or ground wiring.
Less Common Causes
- Faulty coolant pump relay or fuse (vehicle dependent).
- Weak inverter ECU driver output for pump control.
- Clogged coolant passages or collapsed hoses.
- Low coolant level causing cavitation or dry running.
Diagnosis: Step-by-Step Guide
Begin by confirming whether the pump truly fails to activate or if the ECU is misinterpreting a related cooling issue.
Tools You’ll Need: OBD-II scan tool, multimeter, test light, infrared thermometer, coolant funnel/bleeder, wiring diagrams, and insulated gloves.
- Command the pump ON with a scan tool. Listen for humming or buzzing; a silent pump is likely failed.
- Check coolant movement. Remove the reservoir cap and look for turbulence—if none, the pump is stuck OFF.
- Test pump power supply. Verify correct voltage at the connector with the pump commanded ON.
- Check pump ground continuity. Weak or missing ground can prevent pump activation.
- Perform a resistance check on the pump motor. Infinite resistance typically indicates internal failure.
- Inspect the pump connector. Look for green corrosion, loose terminals, or water intrusion.
- Bleed the inverter cooling system. Air pockets can cause pump shutdown and overheating.
- Inspect coolant level and quality. Low coolant or contamination reduces flow.
- Check hoses for blockages. A collapsed hose can mimic a stuck pump.
- Review freeze-frame data. Shows whether overheating occurred during idle, acceleration, or high-load driving.
Pro Tip: Use Mode $06 pump performance metrics (if available) to see commanded pump duty cycle versus actual temperature change—if temperature does not drop with high pump duty, the pump is likely seized internally.
Possible Fixes & Repair Costs
- Replace Motor Electronics Coolant Pump “A”: €150–€350 depending on model.
- Repair or replace corroded wiring or connectors: €40–€150.
- Bleed and refill the inverter cooling system: €40–€120.
- Replace coolant hoses or remove blockages: €30–€120.
- Replace pump fuse or relay (if equipped): €10–€40.
- Replace inverter control driver (rare): €300–€550.
Confirm pump power and flow before replacing high-cost components—most P0A75 issues are solved by pump replacement or fixing wiring faults.
Can I Still Drive With P0A75?
Driving with P0A75 is risky. Without coolant flow, the inverter can overheat rapidly, especially in warm weather or under load. If you notice reduced power, loud cooling fans, or hybrid warnings, stop driving immediately to prevent inverter damage or propulsion shutdown.
Related Codes
- P0A6C – Hybrid Battery Voltage System Isolation Sensor Range/Performance
- P0A9F – Hybrid Battery Temperature Sensor Too Hot
- P0A9E – Hybrid Battery Temperature Sensor Too Cold
- P0A9D – Hybrid Battery Temperature Sensor Range/Performance
- P0A9C – Motor Electronics Coolant Temperature Sensor Circuit High
- P0A9B – Motor Electronics Coolant Temperature Sensor Circuit Low
- P0A9A – Motor Electronics Coolant Temperature Sensor Circuit Range/Performance
- P0A99 – Motor Electronics Coolant Temperature Sensor Circuit
- P0A98 – Hybrid Battery Pack Cooling Fan 2 Performance
- P0A97 – Hybrid Battery Pack Cooling Fan 2 Control Circuit
Key Takeaways
- P0A75 means Motor Electronics Coolant Pump “A” is stuck OFF.
- Most causes involve pump failure, wiring issues, or air pockets.
- Driving with this fault can cause inverter overheating and limp mode.
- Always verify pump power and coolant flow before replacing parts.
FAQ
What causes P0A75 most often?
Usually a failed coolant pump or corroded connector that prevents the pump from turning on.
Is it safe to drive with P0A75?
No. The inverter can overheat quickly without coolant circulation, risking expensive damage.
How do I fix P0A75?
Test pump power, check wiring, bleed the cooling system, and replace the coolant pump if it fails activation tests.
Can an air pocket cause P0A75?
Yes. Air trapped in the inverter cooling system can stop circulation and trigger overheating faults.
Does P0A75 mean the inverter is failing?
Rarely. The pump or wiring is almost always the issue, but prolonged overheating can damage the inverter over time.