P0A73 – Inverter Temperature Too Low

DTC P0A73 – Inverter Temperature Too Low is a hybrid/EV powertrain code that appears when the hybrid control module detects that the inverter temperature sensor is reading abnormally low. This often points to a faulty sensor, wiring issue, or a cooling system problem affecting accurate temperature feedback. You may notice limited electric assist or hybrid warnings. Because the inverter relies on precise temperature data to manage high-voltage circuits, incorrect readings can limit performance. This guide clearly explains the meaning, causes, symptoms, diagnosis, and the most effective fixes for P0A73.

What Does P0A73 Mean?

P0A73 is a generic SAE J2012-DA hybrid-system diagnostic code set when the inverter temperature reading falls below the expected threshold. The hybrid ECU uses this temperature input to regulate cooling flow, inverter load, and power distribution between MG1/MG2. If the signal drops unrealistically low—suggesting a short-to-ground, failed sensor, or disconnected circuit—the ECU flags the code.

The code often appears during cold starts or after repairs when coolant flow or wiring isn’t fully restored. Because inverter temperature is critical for safe power management, the system may limit motor torque to protect the electronics.

P0A73 Quick Reference

  • OBD-II Family Scope: Generic (SAE J2012-DA)
  • System: Hybrid Powertrain / Inverter Temperature Monitoring
  • Difficulty Level: Medium–High
  • Estimated Repair Cost: €120 – €850
  • Last Updated: 03 December 2025

Real-World Example / Field Notes

One case I saw was on a 2013 Lexus CT200h that repeatedly set P0A73 on cold mornings. The owner had recently replaced the inverter coolant pump following a P0A93 fault. During inspection, I found the temperature sensor harness clipped against the pump bracket, cutting partially into the insulation. The ECU saw sudden low readings and set the fault. Repairing the wiring and securing the harness solved it—no inverter replacement needed. With hybrid systems, even minor wiring damage can create misleading temperature data.

Symptoms of P0A73

  • Check Engine Light: MIL or hybrid system warning indicator.
  • Reduced Hybrid Assist: Limited electric motor performance.
  • Higher Engine RPM: Gas engine compensates for restricted inverter output.
  • Poor Cold Start Performance: Inverter runs conservative strategy when temp data is invalid.
  • Cooling Fan Behavior Changes: Fans may run more often due to fail-safe logic.
  • Occasional EV Mode Lockout: Vehicle may disable electric-only operation.

Common Causes of P0A73

Most Common Causes

  • Faulty inverter temperature sensor
  • Short-to-ground or open circuit in the sensor wiring
  • Unseated or corroded temperature sensor connector
  • Cooling system recently serviced with air pockets present
  • Battery or inverter coolant pump drawing low flow

Less Common Causes

  • Hybrid ECU calibration errors
  • Internal inverter temperature sensing IC failure
  • Broken harness near the inverter housing from vibration
  • Damaged high-voltage junction block causing temp-signal interference

Diagnosis: Step-by-Step Guide

Start by confirming the code and examining freeze-frame conditions to see when the low temperature reading occurred.

Tools You’ll Need

An OBD-II scanner with hybrid support, digital multimeter, wiring diagram, test leads, and ideally a thermal camera to compare actual surface temperatures with sensor data.

  1. Verify P0A73 is active. Check for companion codes like P0A70 or P0A71.
  2. Review freeze-frame data. Note ambient temperature and inverter load when the error set.
  3. Inspect sensor connector. Look for corrosion, loose locking tabs, or moisture.
  4. Check continuity of sensor wiring. Test between the sensor and inverter control module.
  5. Compare sensor reading to actual temperature. Use a thermal camera or IR thermometer.
  6. Test for short-to-ground. A very low temperature value often indicates a wiring short.
  7. Inspect coolant flow. Air pockets or low circulation can mislead the ECU.
  8. Check for technical service bulletins (TSBs). Some hybrid models require software updates.
  9. Run a road test. Watch the temperature signal stabilize after warm-up.
  10. Perform wiggle-test on the harness. Intermittent drops often reveal broken strands.

Pro Tip: Use Mode $06 to inspect the inverter temperature sensor’s minimum/maximum limits. If a test result is near threshold, the sensor may be drifting—even if it hasn’t failed outright.

Possible Fixes & Repair Costs

  • Replace inverter temperature sensor – Restores accurate temperature monitoring. €180–€350
  • Repair or replace damaged sensor wiring – Fixes intermittent low readings. €120–€300
  • Bleed the inverter cooling system – Removes air pockets causing false temperature variation. €100–€180
  • Replace inverter coolant pump – If low flow affects temperature stability. €250–€600
  • ECU software update – Addresses logic errors in early hybrid models. €100–€200
  • Inverter replacement – Rare but required for internal sensor failures. €1,000–€2,000+

Confirm the cause before replacing high-voltage components—many P0A73 cases are simple wiring or sensor faults.

Can I Still Drive With P0A73?

Most vehicles will still drive, but hybrid performance may be limited until the temperature sensor behaves normally. If the vehicle enters reduced-power mode or shows hybrid system warnings, avoid long trips. Incorrect temperature readings can lead to overheating if the system cannot manage cooling properly.

Need wiring diagrams and factory-style repair steps?

Powertrain faults often require exact wiring diagrams, connector pinouts, and guided test steps. A repair manual can help you confirm the cause before replacing parts.

Factory repair manual access for P0A73

Check repair manual access

Compare nearby inverter temperature trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • P0A74 – Inverter Temperature Too High
  • P0A9F – Hybrid Battery Temperature Sensor Too Hot
  • P0A9E – Hybrid Battery Temperature Sensor Too Cold
  • P0A93 – Inverter A Cooling System Performance
  • P0A89 – DC/DC Converter Temperature Too High
  • P0A88 – DC/DC Converter Temperature Too Low

Key Takeaways

  • P0A73 means the inverter temperature sensor is reading unrealistically low.
  • Most issues come from wiring faults, failed sensors, or coolant flow problems.
  • Driving is possible but hybrid performance may be reduced.
  • Always compare live temperature data with actual temperature readings.

FAQ

What causes inverter temperature to read too low?

Usually a failed temperature sensor or damaged wiring pulls the signal toward ground. Air pockets in the inverter cooling system can also make the temperature reading inaccurate during cold operation.

How do I fix P0A73?

Begin by checking the sensor connector, wiring integrity, and coolant flow. If readings don’t match actual temperatures, the sensor is likely faulty. Software updates may be required on certain hybrid models.

Can cold weather cause P0A73?

Extremely cold starts can briefly drop inverter temperatures, but the code only sets when values fall below logical limits. If the code repeats, the sensor or wiring is usually to blame.

Is it safe to keep driving?

Short trips are usually safe, but avoid long-distance driving until accurate temperature readings are restored. Incorrect data can cause cooling mismanagement under load.

Does P0A73 mean the inverter is failing?

Not necessarily. Internal inverter failure is rare for this code. Most issues are related to the external temperature sensor or its wiring.