P0A6D means the Hybrid/EV Control ECU has detected a **fault in the Motor Electronics Coolant Pump Control Circuit**. This coolant pump is responsible for circulating coolant through the inverter, power electronics, and sometimes the electric motor housing. When the control circuit experiences an electrical issue—such as an open circuit, short, or incorrect control signal—the pump may run weakly or stop completely. Without proper cooling, the inverter can overheat, forcing the vehicle into limp mode or shutting down electric propulsion. This guide explains what P0A6D means, along with symptoms, causes, diagnosis steps, and repair options.
What Does P0A6D Mean?
P0A6D triggers when the ECU detects that the **control signal to the inverter coolant pump is incorrect or out of specification**. This can happen if the pump doesn’t respond to ECU commands, pulls too much/too little current, or reports an invalid feedback signal.
Most hybrid/EV coolant pumps are electronically controlled brushless motors. The ECU constantly monitors pump speed, electrical load, and response. If the pump fails to activate or the circuit behaves unexpectedly, the ECU sets P0A6D and may limit hybrid operation to prevent overheating.
Quick Reference
- OBD-II Family: P-Code (Hybrid Cooling System)
- Scope: Generic
- System: Power Electronics / Inverter Cooling
- Difficulty Level: Moderate
- Estimated Repair Cost: €150–€600
- Last Updated: 2025-11-24
Real-World Example / Field Notes
We’ve seen P0A6D on Toyota Prius/Camry/RAV4 hybrids, Lexus hybrids, Hyundai Ioniq/Kona hybrids, and GM/Voltec vehicles. In a Prius, the inverter pump failed intermittently due to a worn internal circuit board, causing the inverter temperature to spike during highway driving. A Hyundai Ioniq Hybrid displayed P0A6D because of a corroded pump connector, causing the ECU to see an open-circuit condition. In both cases, the vehicle entered limp mode when the inverter coolant temperature climbed.
Symptoms of P0A6D
- “Check Hybrid System” message: Often appears immediately.
- Limp mode activation: Hybrid power is reduced to protect electronics.
- Inverter overheating: Temperature rises rapidly under load.
- No or weak coolant flow: The pump may not run even when commanded.
- Loud fan operation: Inverter cooling fans may run at maximum speed.
- Shutdown or reduced EV mode: Some systems disable electric drive when hot.
- Vehicle may stall (rare): If inverter temperature protection shuts down power.
Common Causes of P0A6D
Most Common Causes
- Failed inverter coolant pump (internal electronics failure).
- Open circuit in the pump control wiring harness.
- Corroded or loose coolant pump connector.
- Short-to-ground or short-to-power in the pump control wires.
- Low or contaminated coolant causing pump drag or speed errors.
Less Common Causes
- Inverter ECU driver circuit malfunction.
- Blown fuse supplying power to the coolant pump.
- Poor grounding at chassis or inverter frame.
- Coolant blockage or air pocket causing abnormal pump load.
Diagnosis: Step-by-Step Guide
Your goal is to determine whether the pump itself, wiring, power supply, or ECU control driver is causing the malfunction.
Tools You’ll Need: OBD-II scan tool, multimeter, coolant funnel/bleeder, wiring diagrams, thermometer or scan tool temperature data.
- Check live inverter coolant temperature. Rapid rise after startup suggests pump inactivity.
- Command the pump ON with a scan tool. Verify whether the pump starts or remains inactive.
- Listen and feel for pump operation. A healthy pump makes a faint buzzing or humming sound.
- Inspect the pump connector. Look for corrosion, green deposits, loose pins, or water intrusion.
- Check power and ground supply at the pump. Verify correct voltage and continuity.
- Perform a resistance test on the pump motor windings. Out-of-spec values indicate internal failure.
- Test control signal voltage. If no signal is present, check wiring back to the ECU.
- Inspect wiring harness routing. Look for abrasion, pinching, or melted insulation.
- Check coolant level and condition. Low coolant or air pockets cause abnormal pump behavior.
- Review freeze-frame data. Helps determine whether the failure occurred under load, at idle, or during warm-up.
Pro Tip: On many hybrids, the inverter pump runs as soon as the vehicle enters READY mode. If you hear no circulation sound and feel no turbulence in the reservoir, the pump is likely dead—even before testing with a scan tool.
Possible Fixes & Repair Costs
- Replace the inverter coolant pump: €150–€400.
- Repair wiring damage or open circuits: €40–€180.
- Clean or replace corroded connector terminals: €10–€60.
- Replace pump fuse or relay (if equipped): €10–€30.
- Refill and bleed inverter coolant system: €40–€120.
- Replace or repair inverter driver circuit (rare): €300–€600.
Most P0A6D faults stem from bad pumps or corroded connectors. Verify power, ground, and control signal before replacing major components.
Can I Still Drive With P0A6D?
Not recommended. Without proper cooling, the inverter and power electronics can overheat rapidly. The hybrid system may enter limp mode, shut off the electric motor, or disable READY mode to protect itself. Driving with an overheating inverter can cause severe damage—stop immediately if temperatures climb.
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
- P0A6D indicates an electrical fault in the inverter coolant pump control circuit.
- Most failures are caused by bad pumps, wiring damage, or connector corrosion.
- Driving with this fault can cause inverter overheating and limp mode.
- Verify pump operation and electrical supply before replacing components.
FAQ
What causes P0A6D most often?
A failed inverter coolant pump or corroded pump connector is the most common cause of this code.
Can I drive with P0A6D?
It’s unsafe. The inverter can overheat quickly if the pump isn’t running. Stop driving until the issue is diagnosed.
How do I diagnose P0A6D?
Command the pump on with a scan tool, check power/ground, inspect the connector, and test pump resistance and control signals.
Does P0A6D mean the inverter is failing?
Usually not. The pump or wiring is more likely to be the problem. Inverter driver failure is possible but rare.
Does low coolant cause P0A6D?
It can contribute. Air pockets or low coolant can make the pump draw abnormal current or fail to circulate properly.