P0A43 – Drive Motor “A” Temperature Sensor Circuit High

P0A43 means the ECU has detected a **high-voltage condition in the Drive Motor “A” temperature sensor circuit**, which monitors how hot the main electric traction motor gets during driving. “Circuit High” indicates the signal voltage is higher than normal — typically caused by an open circuit, unplugged connector, broken wiring, or an internally open thermistor. When this happens, the ECU can’t trust the temperature reading and may disable EV torque, reduce acceleration, or trigger limp mode to prevent unseen overheating. This guide explains the meaning, causes, diagnosis steps, and the most effective repairs for P0A43.

What Does P0A43 Mean?

P0A43 sets when the Hybrid/EV Powertrain Control Module sees **temperature sensor voltage above the valid range** for Drive Motor “A.” Since these sensors use NTC thermistors, higher voltage corresponds to unrealistically low temperatures. When the circuit is open, the ECU interprets the motor as being extremely cold (often –40°C) — a value impossible during normal operation.

Because traction motor cooling and thermal limits are tightly controlled, the ECU responds quickly by reducing torque or disabling EV propulsion whenever a circuit-high fault is detected.

Quick Reference

  • OBD-II Family: P-Code (Hybrid/EV Powertrain)
  • Scope: Generic
  • System: Drive Motor “A” Temperature Monitoring
  • Difficulty Level: Moderate
  • Estimated Repair Cost: €120–€400
  • Last Updated: 2025-11-24

Real-World Example / Field Notes

P0A43 is common on Toyota/Lexus hybrids, Hyundai/Kia EVs, and GM/Voltec systems. In one Toyota Prius case, Drive Motor A temperature stayed fixed at –40°C regardless of load. The cause was a broken signal wire inside a harness clip that had rubbed through against the inverter cover. On a Kia Niro EV, the thermistor inside the motor failed open, causing the ECU to think the motor was permanently cold and shutting down EV torque on startup. In both cases, the fault was evident immediately on live data.

Symptoms of P0A43

  • Fixed low temperature reading: Commonly –40°C at all times.
  • Reduced EV power: Torque drops to protect the motor.
  • EV mode dropout: Hybrids force the engine to take over.
  • Limp mode: Acceleration becomes restricted.
  • Warning messages: “Check Hybrid System,” “EV System Error,” etc.
  • Cooling pump/fans running hard: The ECU attempts to compensate for unknown motor temperature.
  • READY-mode issues: Severe cases may prevent EV startup.

Common Causes of P0A43

Most Common Causes

  • Open circuit in the temperature sensor signal wire.
  • Broken or unplugged temperature-sensor connector.
  • Failed thermistor inside the drive motor (open resistance).
  • Corroded connector terminals raising resistance.
  • Harness damage from vibration, heat, or road debris.

Less Common Causes

  • Coolant intrusion causing intermittent opens.
  • Internal stator temperature circuit failure.
  • Loose ground reference for the sensor or ECU.
  • Hybrid ECU input-driver malfunction (rare).

Diagnosis: Step-by-Step Guide

Your goal is to find where the circuit is open — in the sensor, wiring, or connector.

Tools You’ll Need: EV-capable scan tool, multimeter, wiring diagram, IR thermometer, coolant bleed tools.

  1. Check live data. A constant –40°C reading indicates a full open circuit.
  2. Inspect the connector. Look for corrosion, loose locking tabs, pushed pins, or coolant contamination.
  3. Perform a wiggle test. Move the harness while watching temperature data — flickers confirm wiring issues.
  4. Measure signal voltage. Higher-than-normal voltage confirms an open circuit.
  5. Test sensor resistance. Infinite resistance at ambient temperature indicates a failed thermistor.
  6. Check wiring continuity. Verify both signal and ground wires between the motor and ECU.
  7. Inspect harness routing. Look for pinch points, crushed insulation, or areas contacting metal brackets.
  8. Confirm actual motor temperature. Use an IR thermometer to compare to live data.
  9. Check freeze-frame data. See if the fault appears immediately at key-on or under load — an immediate fault points to an open circuit.
  10. Verify coolant system operation. Although unrelated to circuit high faults, ensure the cooling loop is functioning normally.

Pro Tip: If the temperature reading stays at –40°C even when the harness is manipulated, the sensor or internal motor thermistor is likely open — not the wiring.

Possible Fixes & Repair Costs

  • Repair open or broken wiring: €10–€100.
  • Clean or replace corroded connectors: €10–€50.
  • Replace Drive Motor “A” temperature sensor (if serviceable): €150–€250.
  • Repair or replace motor stator temperature circuit: €300–€500+ depending on model.
  • Fix coolant leaks near sensor harness: €40–€150.
  • Bleed/restore cooling flow: €40–€120.

Because “circuit high” nearly always indicates an open path, always inspect wiring and connector integrity before replacing the drive motor or major components.

Can I Still Drive With P0A43?

Driving may be possible, but it’s risky. The ECU may reduce torque or shut down EV power because it cannot confirm true motor temperature. If the temperature reading stays at –40°C or if warnings appear, avoid driving until the fault is repaired to prevent motor overheating.

Need HVAC actuator and wiring info?

HVAC door and actuator faults often need connector views, wiring diagrams, and step-by-step test procedures to confirm the real cause before replacing parts.

Factory repair manual access for P0A43

Check repair manual access

Compare nearby drive motor trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • P0A9C – Motor Electronics Coolant Temperature Sensor Circuit High
  • P0A67 – Drive Motor “B” Position Sensor Circuit High
  • P0A63 – Drive Motor “A” Position Sensor Circuit High
  • P0A6F – Motor Electronics Coolant Pump Control Circuit High
  • P0A9B – Motor Electronics Coolant Temperature Sensor Circuit Low
  • P0A9A – Motor Electronics Coolant Temperature Sensor Circuit Range/Performance

Key Takeaways

  • P0A43 indicates a high-voltage (open circuit) fault in Drive Motor “A” temperature sensing.
  • Most causes involve open wiring, bad connectors, or failed thermistors.
  • EV torque may be reduced or disabled to protect the motor.
  • A consistent –40°C reading is the fastest clue to locating the issue.

FAQ

What causes P0A43 most often?

An open circuit — usually a broken wire, unplugged connector, or failed thermistor inside the drive motor.

Why does the temperature show –40°C?

–40°C is the default value the ECU displays when the thermistor circuit is open and no valid signal is received.

Is P0A43 dangerous?

Potentially. If the ECU can’t monitor motor temperature, it may limit power or enter limp mode to prevent overheating damage.

How do I diagnose P0A43?

Inspect connectors, test wiring continuity, check sensor resistance, and compare real motor temperature with IR measurements.

Can I drive with P0A43?

Short distances may be possible, but sudden torque loss or shutdown can occur. Repair the circuit before normal driving.