Wiring fault in the battery power-off control circuit, such as short to earth, chafing or water damage; Poor connection or corrosion at the battery controller or contactor connector; Faulty main contactor or relay in the battery pack, or its control coil; Low 12 V supply or poor earth affecting the battery controller or contactor drive; Faulty battery controller or hybrid control unit; Damage to the pack or its internal wiring after an impact or water ingress.

P0A28

Hybrid/EV Battery Power Off Circuit Low.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
A: AreaHybrid propulsion
28: FaultThe specific fault in that area

What it means

P0A28 is the generic code for a low signal in the circuit that switches the hybrid or EV traction battery power off, such as the contactor, relay or cut-off control. The hybrid control unit or battery controller commanded or monitored this circuit and saw a voltage lower than expected. Exact circuit layout and the trigger conditions vary by model and battery design.

Symptoms

Hybrid or high-voltage system warning light on the dashboard
Car will not go into Ready mode or will not start
Reduced power or limp-home mode
Loss of electric assist or EV driving
Car shuts down unexpectedly while driving
Engine runs constantly with no hybrid assist

Possible causes

Wiring fault in the battery power-off control circuit, such as short to earth, chafing or water damagelikely
Poor connection or corrosion at the battery controller or contactor connectorlikely
Faulty main contactor or relay in the battery pack, or its control coilpossible
Low 12 V supply or poor earth affecting the battery controller or contactor drivepossible
Faulty battery controller or hybrid control unitrare
Damage to the pack or its internal wiring after an impact or water ingressrare

How to diagnose

Read all stored codes and freeze frame data, and note any other high-voltage, battery or interlock codes that appear alongside P0A28.
Check the 12 V battery condition and charging voltage, as a weak supply can upset the control circuits, and check the main earths.
Visually inspect the accessible wiring and connectors for the battery controller and power-off circuit for chafing, corrosion, water and previous repair work.
Only a technician trained in high-voltage systems should continue: follow the manufacturer's procedure to make the system safe and isolate it before touching any orange high-voltage components.
Check the service disconnect or plug is fully and correctly seated, if the model has one.
Use live data to compare the commanded and actual state of the power-off or contactor circuit, where the model supports it.
Test the circuit wiring for continuity, short to earth and supply voltage against the model's wiring diagram.
Test the contactor or relay coil resistance and operation as the manufacturer specifies, as the procedure depends on the model.

How to fix

Repair or replace damaged wiring in the power-off circuit and secure it clear of sharp edges and moisture.
Clean, repair or replace corroded or loose connectors and terminals.
Replace a faulty contactor or relay, or the affected battery pack component, as the manufacturer permits.
Restore the 12 V supply by charging or replacing the battery and repairing poor earths.
Replace or reprogram the battery controller or hybrid control unit only after confirming the fault is internal and an approved update applies.

Can I keep driving?

High severity

Avoid driving it. A fault in the high-voltage power-off circuit can cause sudden loss of drive or a safety shutdown, so have it checked by a high-voltage trained technician.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.