P0A37 Generator Temperature Sensor Circuit Range / Performance

P0A37 Possible Causes

  • Faulty hybrid vehicle engine
  • Hybrid vehicle engine wiring harness open or shorted
  • Poor electrical connection in hybrid vehicle engine circuit

What Does It Mean?

How to Fix Code P0A37

Check the “Possible Causes” listed above. Visually inspect the wiring harness and related connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

P0A37 Possible Symptoms

Check engine light illuminated (or service engine soon warning light)

P0A37 Meaning

Engine temperature sensor No. 2 detects the transmission-differential fluid temperature. The resistance of the thermistor installed in engine temperature sensor No. 2 varies with changes in transmission-differential fluid temperature. The construction of engine temperature sensor No. 2 and how it connects to the HV control ECU are the same as those of engine temperature sensor No. 1.
Based on the signal provided by engine temperature sensor No. 2, the HV control ECU limits the load to prevent engine overheating. Additionally, the HV control ECU checks engine temperature sensor No. 2 for wiring malfunction and the sensor for malfunction.

P0A38 Low Generator Temperature Sensor Circuit

P0A38 Possible Causes

  • Faulty hybrid vehicle motor
  • Hybrid vehicle motor wiring harness open or shorted
  • Poor electrical connection in hybrid vehicle motor circuit

What Does It Mean?

How to Fix Code P0A38

Check the “Possible Causes” listed above. Visually inspect the wiring harness and related connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

P0A38 Possible Symptoms

Check engine light illuminated (or service engine soon warning light)

P0A38 Meaning

Engine temperature sensor No. 2 detects the transmission-differential fluid temperature. The resistance of the thermistor installed in engine temperature sensor No. 2 varies with changes in transmission-differential fluid temperature. The construction of engine temperature sensor No. 2 and how it connects to the HV control ECU are the same as those of engine temperature sensor No. 1.
Based on the signal from engine temperature sensor No. 2, the HV control ECU limits the load to prevent engine overheating. Additionally, the HV control ECU checks engine temperature sensor No. 2 for wiring malfunction and the sensor for malfunction.

P0A39 High Generator Temperature Sensor Circuit

Code Meaning

P0A39 indicates a problem with the hybrid engine’s temperature sensor #2, which monitors the temperature of the transaxle fluid. This sensor uses a thermistor: its electrical resistance varies with the fluid temperature. The hybrid (HV) ECU uses this data to:

  • Limit engine load and prevent overheating.

  • Detect sensor or wiring malfunctions.

Note: Its operation is identical to temperature sensor #1, but it is dedicated to the transaxle.

Visible Symptoms

  • 🔥 Check engine light on (or “Service hybrid system soon” message).

  • No other obvious engine symptoms (the system automatically limits performance to protect the engine).

Probable Causes

Priority Cause Description
1 Electrical Issues Open/short-circuited wiring harness, oxidized/faulty connectors, bent/broken pins.
2 Sensor Failure Thermistor out of specifications (incorrect resistance).
3 HV ECU Failure Rare – check after eliminating other causes.
4 Faulty Hybrid Engine Very unlikely (the code specifically targets the sensor circuit).

Diagnostic Procedure

Required Tools: Digital multimeter, OBD2 scanner, vehicle technical documentation.

  1. Visual Inspection (80% of solutions):

    • Check the sensor wiring harness (physical damage, rodent bites).

    • Inspect the connectors:

      • Bent, broken, or corroded pins.

      • Loose connection or moisture.

      • Clean with contact spray if necessary.

  2. Sensor Electrical Test:

    • Disconnect the connector and measure the resistance between the pins:

      • Expected Value: Varies with temperature (refer to manufacturer documentation).

      • Anomaly: Infinite resistance (open circuit) or zero (short circuit).

  3. Circuit Test to HV ECU:

    • Use the multimeter in continuity mode:

      • Check for no break between the sensor and the ECU.

    • Measure the supply voltage (usually 5V) with the ignition on.

  4. ECU Diagnostic:

    • If the wiring and sensor are intact, suspect an HV ECU failure (use a scanner to check live data).

Common Repairs

  • 🔧 Replacement of temperature sensor #2 (moderate cost).

  • 🔧 Repair of wiring harness/connector (soldering, plug replacement).

  • 💡 Tip: After repair, clear the code and test the vehicle under real conditions (temperature rise).

⚠️ Hybrid Safety: Always shut off the high voltage (follow manufacturer procedures) before any intervention.

Why This Approach?

  • Electrical causes (wiring, connectors) account for 90% of P0A39 cases.

  • The sensor is inexpensive and easy to test – replacing it is a quick solution if resistance values are inconsistent.

  • The ECU or hybrid engine is rarely at fault (replace only as a last resort).

Source: Manufacturer technical data (Toyota/Lexus, Honda, Ford Hybrid).

P0A3A Generator Temperature Sensor Circuit Intermittent

P0A3A Possible Causes

  • Faulty hybrid vehicle engine
  • Hybrid vehicle engine wiring harness open or shorted
  • Poor electrical connection in hybrid vehicle engine circuit

What Does It Mean?

How to Fix Code P0A3A

Check the “possible causes” listed above. Visually inspect the wiring harness and related connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

P0A3A Possible Symptoms

Check engine light illuminated (or service engine soon warning light)

P0A3A Meaning

Engine temperature sensor No. 2 detects the transmission-differential fluid temperature. The resistance of the thermistor installed in engine temperature sensor No. 2 varies with changes in transmission-differential fluid temperature. The construction of engine temperature sensor No. 2 and how it connects to the HV control ECU are the same as those of engine temperature sensor No. 1.
Based on the signal provided by engine temperature sensor No. 2, the HV control ECU limits the load to prevent engine overheating. Additionally, the HV control ECU checks engine temperature sensor No. 2 for wiring malfunction and the sensor for malfunction.

P0A3B Generator Overheating

P0A3B Possible Causes

  • Faulty hybrid vehicle engine
  • Hybrid vehicle engine wiring harness open or shorted
  • Poor electrical connection of hybrid vehicle engine circuit

What Does It Mean?

How to Fix P0A3B Code

Check the “possible causes” listed above. Visually inspect the wiring harness and related connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

P0A3B Possible Symptoms

Check engine light illuminated (or service engine soon warning light)

P0A3B Meaning

Engine temperature sensor No. 2 detects the transmission-differential fluid temperature. The resistance of the thermistor installed in engine temperature sensor No. 2 varies with changes in transmission-differential fluid temperature. The construction of engine temperature sensor No. 2 and how it is connected to the HV control ECU are the same as those of engine temperature sensor No. 1.
Based on the signal provided by engine temperature sensor No. 2, the HV control ECU limits the load to prevent engine overheating. Additionally, the HV control ECU checks engine temperature sensor No. 2 for wiring malfunction and the sensor for malfunction.

P0A3C Drive Motor “A” Temperature Sensor

P0A3C Possible Causes

  •     Faulty drive motor ‘A’ inverter sensor
  •     Drive motor ‘A’ inverter sensor harness is open or shorted
  •     Poor electrical connection in drive motor A inverter sensor circuit

What Does It Mean?

How to Fix Code P0A3C

    Check the “possible causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

P0A3C Possible Symptoms

    Engine light on (or service engine soon warning light)

P0A3C Meaning

The Engine Control Module (ECM) monitors the drive motor ‘A’ inverter overheat sensor. The ECM sets the OBDII code when the drive motor ‘A’ inverter overheat sensor does not meet factory specifications.

P0A3D Drive Motor Inverter Temperature “B

P0A3D Possible Causes

  • Faulty drive motor ‘A’ inverter sensor
  • Drive motor ‘A’ inverter sensor harness is open or shorted
  • Poor electrical connection in drive motor A inverter sensor circuit

What Does It Mean?

How to Fix Code P0A3D

Check the “possible causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

P0A3D Possible Symptoms

Engine light on (or service engine soon warning light)

P0A3D Meaning

The Engine Control Module (ECM) monitors the drive motor ‘A’ inverter overheat sensor. The ECM sets the OBDII code when the drive motor ‘A’ inverter overheat sensor does not meet factory specifications.

P0A3E Generator Inverter Overheating

P0A3E Possible Causes

  • Faulty transmission assembly
  • Faulty transmission control module
  • Vehicle driven beyond design specifications
  • Motor electronics cooling system issues

What Does It Mean?

How to Fix Code P0A3E

Check the “possible causes” listed above. Visually inspect related wiring harnesses and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

P0A3E Possible Symptoms

Engine light on (or service engine soon warning light)

P0A3E Meaning

Indicates that the motor generator inverter has experienced overheating of the 3 temperature sensors

P0A3F Drive Motor “A” Position Sensor Circuit

P0A3F Possible Causes

  • Faulty drive motor generator
  • Drive motor harness is open or shorted
  • Poor electrical connection in the drive motor generator circuit

What Does It Mean?

How to Fix Code P0A3F

Check the “possible causes” listed above. Visually inspect the related wiring harness and connectors. Look for damaged components and check for broken, bent, pushed out, or corroded connector pins.

P0A3F Possible Symptoms

Engine light on (or service engine soon warning light)

P0A3F Meaning

The drive motor position sensor is monitored by the engine control module. The engine control module monitors the angular position, speed, and direction of the drive motor generator rotor based on signals from the resolver-type position sensor. The position sensor contains a drive coil, two driven coils, and an irregularly shaped metal rotor. The metal rotor is mechanically attached to the drive motor-generator shaft. When the vehicle is turned on, the engine control module sends a 7V AC, 10 kHz excitation signal to the drive coil. The drive coil excitation signal creates a magnetic field surrounding the two driven coils and the irregularly shaped rotor. The engine control module then monitors the two driven coil circuits for a return signal. The position of the irregular metal rotor causes the magnetically induced return signals from the driven coils to vary in size and shape. Comparing the two signals from the driven coils allows the engine control module to determine the exact position, speed, and direction of the drive motor-generator rotor. The position sensor is a non-repairable part of the drive motor.

P0A40 Drive Motor “A” Position Sensor Circuit Range/Performance

P0A40 Possible Causes

  • Faulty drive motor generator
  • Drive motor harness is open or shorted
  • Poor electrical connection in drive motor generator circuit

What Does It Mean?

How to Fix Code P0A40

Check the “possible causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

P0A40 Possible Symptoms

Malfunction Indicator Light illuminated (or Service Engine Soon warning light)

P0A40 Meaning

The drive motor position sensor is monitored by the motor control module. The motor control module monitors the angular position, speed, and direction of the drive motor generator rotor based on signals from the resolver-type position sensor. The position sensor contains one drive coil, two driven coils, and an irregularly shaped metal rotor. The metal rotor is mechanically attached to the drive motor-generator shaft. When the vehicle is turned on, the motor control module delivers a 7V AC, 10 kHz excitation signal to the drive coil. The drive coil excitation signal creates a magnetic field surrounding the two driven coils and the irregularly shaped rotor. The motor control module then monitors the two driven coil circuits for a return signal. The position of the irregular metal rotor causes the magnetically induced return signals from the driven coils to vary in size and shape. A comparison of the two signals from the driven coils allows the motor control module to determine the exact position, speed, and direction of the drive motor-generator rotor. The position sensor is a non-repairable part of the drive motor.