P0A66
Drive Motor B Phase U Current.
- Generic
- Powertrain
- Generic code
- High severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- A
- AreaHybrid propulsion
- 66
- FaultThe specific fault in that area
What it means
P0A66 is a generic hybrid or electric vehicle code relating to the phase U current of drive motor B. The motor inverter or hybrid control unit monitors the current in each motor phase. It set this code because the phase U current reading was faulty, implausible or out of range, or did not match what the controller commanded. Exact set conditions and the location of drive motor B vary by manufacturer and model.
Symptoms
- Hybrid or EV system warning light on the dashboard
- Reduced power or limp-home mode
- Car refuses to enter READY mode or will not move
- Jerky, rough or uneven motor response under acceleration
- Sudden loss of drive while moving
- Engine running more than normal on a hybrid, with poor economy
Possible causes
- Faulty phase U current sensor or sensing circuit inside the inverterlikely
- Damaged, loose or corroded motor phase cable or high-voltage connector at the inverter or motorlikely
- Inverter or power module fault affecting phase U outputpossible
- Drive motor B winding fault or insulation breakdownpossible
- Wiring fault or poor connection in the sensor signal circuit to the control unitpossible
- Low or unstable 12 V supply or poor earth affecting the inverter control electronicspossible
- Faulty or outdated control unit softwarerare
How to diagnose
- Read all stored and pending codes with freeze frame data, noting speed, load, temperature and system state when the fault set, and check for related inverter, motor position or insulation codes.
- Check the 12 V battery condition and charging, as low voltage can cause false inverter faults.
- Visually inspect the inverter and motor wiring, connectors and coolant hoses for damage, corrosion, water ingress or heat marks, once the high-voltage system has been made safe by a suitably trained technician.
- Inspect the low-voltage sensor connectors and wiring to the inverter for pins that are loose, bent or corroded, and for chafing.
- Using live data, compare the phase U current reading with the other phases and with the commanded current, if the vehicle shows these values.
- Following the manufacturer's procedure, with the system isolated, measure the motor winding resistance and insulation resistance on phase U compared with the other phases.
- Check inverter coolant level and cooling circuit operation, as overheating can cause current faults.
- Check for any software updates or technical bulletins for the model before replacing major components.
How to fix
- Repair or replace damaged motor phase cables, high-voltage connectors or low-voltage wiring, and secure the connections to the specified torque.
- Replace or repair the inverter assembly if the current sensing or power stage is faulty, following the manufacturer's procedure.
- Replace drive motor B if winding or insulation faults are confirmed.
- Restore a healthy 12 V supply by repairing or replacing the battery or correcting earth faults.
- Update the control unit software only if the manufacturer lists an outdated or faulty calibration as a cause for this code.
- Clear the code after repair and road test to confirm it does not return.
Can I keep driving?
Avoid driving with this code present, as power can be lost without warning and the fault may involve the high-voltage system. Have it inspected by a technician trained in hybrid and electric vehicles before further use.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.