P0A56

What it means

P0A56 means the hybrid or electric vehicle control unit has judged the signal from the Drive Motor 'B' current sensor to be implausible or out of its expected range. The sensor is still producing a signal, but the value does not match what the inverter and motor control are commanding or what other sensors report. Which sensor, phase and motor 'B' refers to depends on the vehicle and drive system layout.

Symptoms

• Hybrid or EV system warning light on, often with the malfunction indicator lamp
• Reduced power or limp-home mode
• Loss of electric assist or reduced electric drive
• Rough or jerky acceleration under electric power
• Engine running more than normal on a hybrid, or the car refusing to go into Ready mode

Possible causes

• Faulty drive motor current sensor or its internal electronicslikely
• Damaged wiring, poor connector contact or corrosion in the current sensor circuitlikely
• Fault in the inverter or motor control module affecting how the current signal is read or processedpossible
• Low or unstable 12 V supply or poor earths affecting the sensor reference or signalpossible
• Motor winding or high-voltage cable fault causing real current to differ from the commanded valuepossible
• Outdated or faulty control unit software where the manufacturer has issued a known correctionrare

How to diagnose

1. Read all stored and pending codes and record the freeze frame data, noting load, speed and battery state when the code set, and look for related inverter, motor or position sensor codes.
2. Check the 12 V battery condition and charging voltage, as low voltage can cause false sensor faults, and fix any such problems before going further.
3. Visually inspect the sensor wiring and connectors between the motor, inverter and control unit for chafing, water ingress, corrosion, bent pins and loose fits, without opening any high-voltage components.
4. Check live data for the motor 'B' current reading against the commanded current and the other motor or phase readings, at rest and under light load, looking for offsets, noise or dropouts.
5. Check the sensor supply, reference and signal circuits for correct voltage, continuity and short circuits using the manufacturer's procedure for your model.
6. Only a technician trained in high-voltage systems should isolate the high-voltage system and test motor winding insulation and resistance, following the manufacturer's safe working procedure.
7. Check for manufacturer service bulletins and software updates relevant to the vehicle and code.
8. Clear the code after repair and road test, confirming it does not return and the live data is plausible.

How to fix

• Repair or replace damaged wiring and clean or replace corroded or damaged connectors in the sensor circuit.
• Replace the drive motor current sensor or the assembly that contains it, as specified for the model.
• Repair or replace the inverter or motor control unit if diagnosis shows it is misreading or faulty.
• Restore proper 12 V battery and earth condition if low voltage or poor earths caused the fault.
• Repair or replace the motor or high-voltage cabling if testing shows a genuine winding or insulation fault.
• Update the control unit software only where the manufacturer lists an outdated calibration as a known cause.

Can I keep driving?

Nearby codes

• P0A55GenericDrive Motor B Current Sensor Circuit
• P0A57GenericDrive Motor B Current Sensor Circuit Low