P0A15 – Engine Mount Control Circuit Low

P0A15 means the ECU has detected a **fault in the Drive Motor “B” Inverter Temperature Sensor circuit**. This sensor monitors the temperature of the inverter that powers Drive Motor “B” (often the rear motor on AWD hybrids/EVs). A circuit fault means the signal is missing, electrically incorrect, or out of range. Because the inverter handles high voltage and creates significant heat, inaccurate temperature readings trigger protective limits on torque or EV operation. This guide explains what P0A15 means, the symptoms, causes, diagnosis steps, and the repairs that typically fix this inverter temperature circuit problem.

What Does P0A15 Mean?

P0A15 sets when the ECU detects that the Drive Motor “B” inverter temperature sensor circuit is not behaving correctly. Most inverter temperature sensors use NTC thermistors; if voltage is too high, too low, or completely missing, the ECU considers the reading invalid. Since Drive Motor “B” may provide AWD capability or additional propulsion, the system must protect it from overheating.

When P0A15 is active, the ECU may disable the rear motor, reduce EV power, raise cooling fan speed, or enter limp mode to prevent possible inverter overheating.

Quick Reference

  • OBD-II Family: P-Code (Hybrid/EV Powertrain)
  • Scope: Generic
  • System: Drive Motor “B” Inverter Temperature Monitoring
  • Difficulty Level: Moderate
  • Estimated Repair Cost: €100–€350
  • Last Updated: 2025-11-24

Real-World Example / Field Notes

P0A15 is seen on AWD Toyota/Lexus hybrids (e-AWD), Hyundai/Kia PHEVs, and dual-motor EVs. One Lexus RX450h example showed the rear motor shutting off completely during acceleration. Scan data revealed a stuck inverter temperature reading at 135°C despite the vehicle being cold. The cause was a corroded sensor connector on the rear inverter assembly. Cleaning the terminals and repairing a damaged insulation section restored normal AWD function. On a Hyundai Kona Electric AWD variant, coolant seepage at the rear inverter plate intermittently shorted the sensor.

Symptoms of P0A15

  • Loss of AWD/Rear motor assistance: Rear motor may shut off completely.
  • Reduced EV power: ECU limits torque to protect the inverter.
  • Cooling fan running constantly: System tries to compensate for invalid data.
  • Unrealistic inverter temperature readings: Extremely high or low values.
  • Warning lights: “AWD System Malfunction,” “Check Hybrid System,” or “EV System Error.”
  • Limp mode: Acceleration may be restricted.
  • EV mode dropout: Hybrid switches to engine power more often.

Common Causes of P0A15

Most Common Causes

  • Damaged or corroded inverter temperature sensor connector.
  • Chafed wiring near the rear inverter housing.
  • Coolant intrusion into the sensor connector.
  • Failed NTC thermistor inside the sensor (open or shorted).
  • Short-to-ground or short-to-power in the signal wire.

Less Common Causes

  • Inverter coolant pump failure (if a shared pump cools both inverters).
  • Air pockets or low coolant in the rear inverter cooling loop.
  • Incorrect coolant type affecting thermal transfer.
  • ECU signal interpretation faults (rare).
  • Internal inverter PCB sensor line damage.

Diagnosis: Step-by-Step Guide

Your goal is to determine whether the fault comes from the sensor, its wiring, or the inverter cooling system.

Tools You’ll Need: EV/hybrid scan tool, multimeter, wiring diagram, IR thermometer, coolant tools, and access to the rear inverter assembly.

  1. Check live temperature data. A fixed –40°C indicates an open circuit; 150°C indicates a short-to-ground.
  2. Inspect the sensor connector. Look for coolant residue, bent pins, corrosion, or loose locking tabs.
  3. Perform a wiggle test. Flex the wiring harness with live data displayed — sudden changes indicate intermittent wiring faults.
  4. Check for coolant leaks. Rear inverters often sit low and are more exposed to spray and corrosion.
  5. Test sensor resistance. Compare to OEM specifications at room temperature.
  6. Test for circuit shorts. Use a multimeter to check signal wire continuity to ground or power.
  7. Verify rear inverter cooling flow. Some AWD systems share pumps; confirm proper operation.
  8. Bleed cooling system. Air pockets cause misleading thermal behavior.
  9. Compare IR thermometer readings. Confirms whether scan data reflects real temperatures.
  10. Check companion codes. Cooling system performance codes help identify underlying issues.

Pro Tip: If the rear motor cuts out under load but inverter case temperature is normal on IR, the fault is almost certainly electrical — not thermal.

Possible Fixes & Repair Costs

  • Repair or replace damaged wiring: €10–€100.
  • Clean or replace corroded connector terminals: €10–€50.
  • Replace Drive Motor “B” inverter temperature sensor: €100–€200.
  • Fix rear inverter coolant leaks: €40–€150.
  • Bleed/flush cooling system: €40–€120.
  • Replace coolant pump (if applicable): €120–€350.

Because wiring and connector issues are very common on rear-mounted inverters, always inspect those thoroughly before replacing the sensor.

Can I Still Drive With P0A15?

You can usually drive, but with restrictions. The rear motor may remain disabled, reducing traction, acceleration, and stability in slippery conditions. Prolonged driving without accurate inverter temperature monitoring risks overheating. Repair the issue promptly, especially if you rely on AWD capability.

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

  • P0A15 indicates a circuit fault in the Drive Motor “B” inverter temperature sensor.
  • Common causes include wiring damage, connector corrosion, and failed sensors.
  • The ECU may disable the rear motor or limit EV performance.
  • Live data and connector inspection are the fastest diagnostic tools.

FAQ

What causes P0A15 most often?

Corroded connectors, coolant contamination, or damaged wiring near the rear inverter are the most common causes.

Why is my AWD system disabled?

The ECU disables Drive Motor “B” if it cannot trust the inverter temperature sensor. This prevents overheating damage.

Is P0A15 dangerous?

It can be. If the inverter overheats without proper monitoring, severe damage can occur. The system also may reduce traction.

How do I diagnose P0A15?

Check live data for unrealistic temperatures, inspect the connector, test sensor resistance, look for wiring faults, and verify cooling system function.

Can I still drive with P0A15?

Yes, but AWD capability may be lost and EV power reduced. Repair the issue soon to protect the inverter.