P0A42

What it means

P0A42 means the hybrid or electric vehicle control unit has detected a signal voltage that is too high in the circuit for the drive motor 'A' position sensor. This sensor, usually a resolver or similar rotor position sensor, tells the inverter exactly where the motor rotor is so it can time the power to the motor windings. The fault sets when the position signal sits above its expected range, which points to a wiring, connector, sensor or inverter fault.

Symptoms

• Hybrid or EV system warning light on, often with the main warning light
• Reduced power or limp mode
• Car will not go into Ready mode or will not move
• Engine may run more than normal in a hybrid, or the car may shut down the electric drive
• Rough or jerky drive, or sudden loss of drive while moving

Possible causes

• Damaged, chafed or shorted wiring in the motor position sensor circuit, for example a short to a voltage supplylikely
• Corroded, loose or water-damaged connector at the motor or inverterlikely
• Faulty drive motor position sensor (resolver) or its internal windingpossible
• Open circuit in the sensor return or signal wire causing a high readingpossible
• Fault in the inverter or motor control module's sensor interface circuitpossible
• Outdated or faulty control unit software, where the manufacturer has identified this as a known cause for the modelrare

How to diagnose

1. Read all stored codes and freeze frame data, noting whether other motor, inverter or position sensor codes are present and under what conditions the fault set
2. Check for manufacturer service bulletins and known issues for the specific model and motor type, as the sensor layout varies
3. Make sure the high voltage system is properly isolated and that only suitably trained staff work on it, following the manufacturer's safe working procedure
4. Visually inspect the position sensor wiring and connectors at the motor and inverter for chafing, corrosion, moisture, bent pins and poor locking
5. Check live data for the motor position or rotor angle and motor speed, and see whether the reading is stuck, erratic or out of range
6. With the system safely isolated, test the sensor circuit for shorts to voltage, open circuits and high resistance, and test the sensor winding resistance against the manufacturer's specification
7. Wiggle test the harness while watching live data to find intermittent faults
8. If the wiring and sensor test good, check the inverter or control unit supply and grounds, then follow the manufacturer's procedure to confirm a control unit fault

How to fix

• Repair or replace damaged wiring in the position sensor circuit, using the correct high-quality repair method for the model
• Clean, dry or replace corroded or damaged connectors and terminals, and fix any water ingress
• Replace the drive motor position sensor or the motor assembly if the sensor is not serviced separately, and perform any required sensor learn or calibration procedure
• Repair or replace the inverter or motor control unit if it is confirmed faulty, with any required programming
• Update the control unit software only if the manufacturer lists it as a fix for this fault
• After repair, clear the code and road test to confirm it does not return

Can I keep driving?

Nearby codes

• P0A41GenericDrive Motor A Position Sensor Circuit Low
• P0A43GenericDrive Motor A Position Sensor Circuit Intermittent