P0A6F means the Hybrid/EV Control ECU has detected a **high-voltage condition in the Motor Electronics Coolant Pump control circuit**. This electronically controlled pump circulates coolant through the inverter and power electronics. A “Circuit High” fault usually indicates an **open circuit, disconnected connector, broken wire, or internally open pump motor**, causing the control signal or feedback line to float higher than normal. When the pump doesn’t respond correctly, the inverter can overheat, forcing the vehicle into limp mode or blocking READY mode entirely. This guide explains exactly what P0A6F means, the causes, symptoms, diagnosis steps, and repair options.
What Does P0A6F Mean?
The ECU sets P0A6F when the coolant pump’s control or feedback signal voltage registers **higher than the expected operating range**. This typically happens when the circuit is open—meaning the ECU’s output is not being loaded by the pump, creating an abnormally high voltage.
Because the inverter relies on continuous coolant circulation, a failed or non-responsive pump triggers protective logic. The hybrid system may limit motor power, disable EV mode, or completely block system startup if temperatures rise.
Quick Reference
- OBD-II Family: P-Code (Hybrid Cooling System)
- Scope: Generic
- System: Inverter / Motor Electronics Cooling
- Difficulty Level: Moderate
- Estimated Repair Cost: €150–€550
- Last Updated: 2025-11-24
Real-World Example / Field Notes
P0A6F shows up across Toyota/Lexus hybrids, Hyundai/Kia hybrids, Ford hybrids, and GM/Voltec systems. A Toyota Prius presented P0A6F after a coolant pump connector came loose during an engine swap—the ECU saw an open circuit and immediately disabled the inverter pump. A Kia Niro Hybrid had a broken control wire near the pump bracket, causing intermittent circuit-high spikes that appeared only during acceleration. Both vehicles overheated the inverter when the pump wasn’t working as commanded.
Symptoms of P0A6F
- Hybrid/EV warning messages: Typically triggered within seconds of READY mode.
- Inverter overheating: Coolant stops circulating, temperatures rise quickly.
- Limp mode: System reduces electric power to protect components.
- No coolant flow in the reservoir: Clear sign of pump inactivity.
- Cooling fans running at full speed: Compensation for lack of pump flow.
- EV mode disabled: System avoids high inverter loads.
- READY mode refusal (severe): System blocks startup if overheating risk is detected.
Common Causes of P0A6F
Most Common Causes
- Open circuit in the pump control or feedback wiring.
- Disconnected or loose coolant pump connector.
- Internally open inverter coolant pump (motor windings or electronics).
- Broken or damaged harness near the pump bracket.
- Corroded connector pins causing loss of electrical continuity.
Less Common Causes
- Fault in the inverter output driver for the coolant pump.
- Blown pump power fuse or relay (vehicle dependent).
- Poor grounding of the inverter or pump assembly.
- Coolant contamination entering the pump electronics.
Diagnosis: Step-by-Step Guide
Your goal is to locate the **open circuit** that’s causing the abnormally high signal. Most P0A6F issues are simple wiring or pump failures.
Tools You’ll Need: Scan tool, multimeter, wiring diagrams, coolant bleeder, insulated gloves, and access to inverter temperature data.
- Check inverter coolant temperature on live data. Rising temperature indicates poor or no circulation.
- Command the coolant pump ON. If the pump doesn’t respond, proceed to electrical checks.
- Inspect the pump connector. Ensure it’s fully seated and free of corrosion.
- Perform continuity checks on the control wire. High/infinite resistance confirms an open circuit.
- Check for blown pump fuses (if equipped). Some hybrids use a dedicated fuse or module.
- Verify pump ground. A broken or loose ground can cause circuit-high conditions.
- Check the pump’s internal resistance. Infinite resistance indicates internal open windings.
- Look for wiring damage. Abrasion near engine mounts, coolant hoses, or brackets is common.
- Bleed the coolant system. Air pockets are not a cause of P0A6F, but they worsen overheating symptoms.
- Review freeze-frame data. Helpful for identifying whether the fault occurred at idle or under load.
Pro Tip: A quick touch test helps—if the pump stays completely cold during READY mode, it’s likely not running at all, confirming either an open pump motor or an open control circuit.
Possible Fixes & Repair Costs
- Reconnect or replace loose/damaged pump connector: €10–€60.
- Repair open or broken wiring: €40–€180.
- Replace the inverter coolant pump: €150–€400.
- Replace pump fuse or relay (if applicable): €10–€40.
- Repair inverter control output (rare): €300–€550.
- Refill and bleed the coolant system after repairs: €40–€120.
Most P0A6F cases are caused by a disconnected pump, broken wire, or failed motor. Always verify electrical continuity before replacing expensive inverter components.
Can I Still Drive With P0A6F?
Driving with P0A6F is risky. When the inverter coolant pump isn’t running, the system overheats quickly—especially during acceleration or high-load EV operation. If the inverter temperature spikes, the vehicle may enter limp mode or disable propulsion entirely. Stop driving if overheating warnings appear.
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
- P0A6F indicates a high-voltage/open-circuit condition in the inverter coolant pump control circuit.
- Most causes involve open wiring, loose connectors, or a failed pump motor.
- Driving can overheat the inverter and trigger limp mode or shutdown.
- Check continuity, connectors, and pump resistance before replacing major parts.
FAQ
What causes P0A6F most frequently?
Typically an open circuit—broken wiring, a loose connector, or an internally open coolant pump motor.
Can I drive with P0A6F?
Not safely. If the pump isn’t running, the inverter can overheat quickly. Stop driving if warnings appear.
How do I diagnose P0A6F?
Check pump activation with a scan tool, test continuity, inspect connectors, verify ground, and measure pump resistance.
Does P0A6F mean the pump is bad?
Often yes, but wiring faults are equally common. Always confirm with continuity and resistance checks.
Can low coolant cause P0A6F?
Low coolant won’t trigger P0A6F directly, but it can worsen overheating symptoms when the pump is inactive.