P0A05 means the ECU has detected a problem in the **Drive Motor “A” Temperature Sensor circuit** — the sensor that monitors the operating temperature of the primary electric drive motor in a hybrid or electric vehicle. When this circuit fails, the ECU cannot determine how hot the drive motor is, which can trigger reduced power, inverter protection mode, or complete loss of electric assist. You may notice warning lights, limited performance, or overheating alerts. This guide explains exactly what P0A05 means, what causes it, the symptoms, how to diagnose it, and the repairs that typically fix this electric-drive temperature sensor fault.
What Does P0A05 Mean?
P0A05 sets when the ECU reads an implausible, missing, or unstable voltage from the Drive Motor “A” Temperature Sensor. This sensor is usually an NTC thermistor embedded in or attached to the electric motor housing. Its job is to provide real-time temperature information so the ECU can manage torque output, inverter cooling, and thermal protection strategies.
If the reading becomes invalid due to a sensor failure, wiring issue, or connector fault, the ECU cannot accurately assess motor temperature. To prevent motor overheating or insulation damage, the system may reduce or disable electric drive and switch the vehicle into limp mode.
Quick Reference
- OBD-II Family: P-Code (Hybrid/EV Powertrain)
- Scope: Generic
- System: Drive Motor Temperature Monitoring
- Difficulty Level: Moderate to High
- Estimated Repair Cost: €80–€400
- Last Updated: 2025-11-24
Real-World Example / Field Notes
P0A05 is commonly seen on Toyota Prius, Lexus hybrids, Chevrolet Volt, Nissan Leaf, and Hyundai/Kia EV and hybrid models. One Toyota Highlander Hybrid case involved intermittent loss of electric drive on steep highway climbs. Live data showed the motor temperature suddenly jumping to over 150°C, then dropping to normal within seconds — a classic example of a failing temperature sensor connector. Cleaning and reseating the connector fixed the issue. On the Nissan Leaf, P0A05 has been caused by corrosion at the motor temperature sensor harness where road spray accumulates near the front subframe.
Symptoms of P0A05
- Reduced electric power: ECU limits torque to protect the motor.
- Limp mode: Vehicle may rely heavily on the gasoline engine (hybrids).
- Warning messages: “EV System Error,” “Check Hybrid System,” or “Motor Overheating.”
- Intermittent electric drive loss: Vehicle may switch between EV and engine without command.
- Cooling fans running excessively: ECU compensates for uncertain sensor data.
- Overheating alerts: The system may assume a hot motor even if temperature is normal.
- Check Engine Light: P0A05 may appear with inverter or motor control codes.
Common Causes of P0A05
Most Common Causes
- Failed Drive Motor “A” temperature sensor.
- Loose or corroded sensor connector.
- Damaged wiring harness near the motor/inverter.
- Coolant or oil intrusion into the connector.
- Open or short-to-ground in the sensor circuit.
Less Common Causes
- Motor overheating causing thermal drift in the sensor.
- ECU input circuit malfunction (rare).
- Improper coolant flow (hybrid systems with motor cooling jackets).
- Air pockets in motor cooling loop (liquid-cooled electric motors).
- Sensor mounting damage or poor thermal contact.
Diagnosis: Step-by-Step Guide
Your goal is to confirm whether the problem is the sensor, wiring, connector, or a true temperature issue affecting the motor.
Tools You’ll Need: Hybrid/EV-capable OBD-II scanner, multimeter, IR thermometer, wiring diagram, cooling system tools (for liquid-cooled motors), and basic hand tools.
- Check live data for Drive Motor “A” temperature. Look for unrealistic readings such as –40°C, 150°C+, or rapid fluctuations.
- Inspect the sensor connector. Check for corrosion, coolant/oil residue, loose pins, or moisture intrusion.
- Perform a wiggle test. Move the harness gently while watching live data. Sudden changes indicate wiring or connector issues.
- Check wiring for damage. Look for chafing or heat damage near the motor or inverter, where temperatures are highest.
- Measure sensor resistance. Compare readings to manufacturer charts at ambient temperature.
- Check for open or short circuits. Use a multimeter to test for continuity and unwanted grounding.
- Use an IR thermometer. Compare actual motor casing temperature with live data values.
- Inspect cooling system (if equipped). Low coolant, air pockets, or clogged passages can cause actual overheating.
- Check for companion codes. Codes like P0A2F (Drive Motor Temperature Sensor Circuit) help confirm problem areas.
- Evaluate ECU signal input. If wiring and sensor check out, the issue may be within the motor control ECU (rare).
Pro Tip: If the drive motor temperature reading is stuck at –40°C or another implausible value, the circuit is likely open. If it reads extremely high, suspect a short-to-ground or internally shorted sensor.
Possible Fixes & Repair Costs
- Replace Drive Motor “A” Temperature Sensor: €80–€200.
- Repair wiring or connectors: €10–€80.
- Clean or replace corroded connector: €10–€40.
- Fix coolant leaks near the sensor (if liquid-cooled): €20–€120.
- Bleed or flush the motor cooling system: €40–€120.
- Replace coolant pump (if motor is liquid-cooled): €100–€350.
Because P0A05 is often caused by wiring and connector issues, always test the harness before replacing the sensor or motor components.
Can I Still Drive With P0A05?
Driving with P0A05 is risky. The ECU may severely limit or disable electric drive if it cannot determine motor temperature, especially during acceleration or high load. Overheating the drive motor can cause permanent internal damage. Short, gentle driving might be possible, but repair the issue as soon as possible.
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
- P0A05 indicates a fault in the temperature sensor circuit for Drive Motor “A.”
- Most causes involve wiring, connector issues, or a failing sensor.
- Driving is possible but risky due to overheating and loss of EV power.
- Live data, resistance checks, and connector inspection are essential for diagnosis.
FAQ
What causes P0A05 most commonly?
Corroded connectors, broken wiring, or a failing thermistor inside the drive motor temperature sensor are the most frequent causes.
Is P0A05 dangerous?
Yes. If the ECU cannot determine motor temperature, it may disable electric drive or fail to prevent overheating, risking expensive motor damage.
Where is the Drive Motor “A” Temperature Sensor located?
Usually embedded in or mounted on the electric drive motor housing, often near the inverter connection or cooling jacket inlet.
Can low coolant cause P0A05?
On liquid-cooled motors, yes — low coolant or air pockets can lead to erratic temperature readings or actual overheating.
How do I fix P0A05?
Inspect wiring, clean the connector, check resistance, compare live data with IR temperature checks, and replace the sensor if readings remain invalid.