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DTC codes / P0Axx · Hybrid propulsion / P0A42

P0A42Drive Motor A Position Sensor Circuit High

P0A42 indicates that the hybrid or electric vehicle control module has detected an abnormally high voltage signal from the position sensor circuit of drive motor A, which is the primary traction motor. The sensor normally reports the motor's rotor position to the controller so it can synchronize phase currents; a high signal means the circuit is likely open, shorted to voltage, or the sensor's internal resistance has shifted out of range.

SystemPowertrain
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the check engine light or hybrid system warning lamp, often with no other noticeable symptoms
  • Reduced power or a limp-home mode that limits vehicle speed
  • The hybrid system may refuse to start or may shut down shortly after startup
  • Rough or erratic operation of the electric drive motor, including shuddering during acceleration
  • A stored code in the hybrid control module accompanied by a message on the driver information display
  • In some cases, the gasoline engine may run continuously because the hybrid system cannot reliably control the motor

Common causes, most likely first

  1. An open circuit or high resistance in the position sensor signal wire, commonly due to a broken wire or corroded connector terminal
  2. A short to voltage on the sensor signal circuit, often from chafed insulation contacting a power wire
  3. A failed motor position sensor, such as a damaged internal winding or hall-effect element
  4. A poor ground connection for the sensor or the motor housing, causing a reference voltage shift
  5. A faulty hybrid control module or inverter assembly that misreads the sensor signal
  6. Contamination or debris inside the motor housing that interferes with the sensor's magnetic pickup
  7. A damaged resolver or sensor rotor inside the drive motor, usually after mechanical work or a collision

How to diagnose and fix it

  1. Connect a scan tool and record all hybrid system freeze-frame data, then clear the code and test-drive to see if it returns immediately
  2. Visually inspect the motor position sensor connector and harness for corrosion, loose pins, or chafed wires, and repair as needed
  3. Measure resistance and voltage on the sensor signal circuit at the sensor connector and compare with the factory specification
  4. Check the sensor ground circuit for excessive resistance by measuring voltage drop from the sensor ground pin to the chassis
  5. Perform a wiggle test on the harness while watching live sensor data to catch intermittent opens or shorts
  6. If the circuit checks out, remove and inspect the position sensor for physical damage or contamination, and replace it if faulty
  7. As a last step, substitute a known-good hybrid control module or inverter only after confirming all wiring and sensor tests pass

What a high signal really tells you

  • A high signal voltage does not automatically mean the sensor has failed; an open signal wire will pull the reference voltage high, so always check continuity before condemning the sensor.
  • Corroded terminals inside the motor connector are a frequent cause on vehicles that operate in wet or salty environments, and the corrosion often hides behind the connector seal.
  • The position sensor shares its reference voltage with other sensors in some designs, so a fault in a related circuit can drag the signal high and set P0A42 as a side effect.
  • After replacing a motor position sensor, some vehicles require a relearn or calibration procedure with the scan tool, otherwise the code may reset even though the repair is correct.
  • A weak or failing 12-volt auxiliary battery can cause erratic reference voltages that mimic a sensor fault, so load-test the battery before diving into hybrid wiring.

Can I keep driving with P0A42?

Do not continue driving with P0A42 because the hybrid controller may lose accurate motor position and command incorrect phase currents, which can lead to sudden loss of power or damage to the inverter. Have the vehicle towed to a qualified hybrid repair facility and avoid any further operation until the circuit is diagnosed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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