Common OBD II Codes

essential Prius fault codes categorized by system.

🔴 Hybrid System & High-Voltage Battery

• P0A80 – Replace Hybrid Battery Pack (Internal cell failure)
• P3000 – HV Battery Malfunction (General system error/communication)
• P0AA6 – Hybrid Battery Isolation Fault (Voltage leak to chassis)
• P0A93 – Inverter Cooling System Performance (Inverter pump failure)
• P0A7F – Hybrid Battery Deterioration (Battery reaching end of life)
• P0A1D – Hybrid Control Module RAM Error (ECU internal fault)
• P0A0D – High Voltage System Interlock Circuit High (Service plug loose)
• P3011–P3024 – Battery Block 1 through 14 Weak (Specific module failure)

🟠 Engine & Emissions (Check Engine Light)

• P0420 – Catalyst System Efficiency Below Threshold (Catalytic converter)
• P0171 – System Too Lean (Air/fuel mixture off; usually dirty MAF)
• P0300 – Random or Multiple Cylinder Misfire (Plugs, coils, or head gasket)
• P0401 – Exhaust Gas Recirculation (EGR) Flow Insufficient (Clogged valve)
• P3190 – Poor Engine Power (Engine failing to stay running/out of gas)
• P0101 – Mass Air Flow (MAF) Sensor Circuit Range/Performance
• P0125 – Insufficient Coolant Temp for Closed Loop (Stuck thermostat)
• P0505 – Idle Control System Malfunction (Dirty throttle body)

🟡 Braking & Stability Control

• C1256 – Accumulator Low Pressure (Brake actuator failure)
• C1391 – Abnormal Leak in Accumulator (Brake booster assembly leak)
• C1241 – Low Battery Positive Voltage (Commonly a dying 12V battery)
• C1259 – HV System Regenerative Braking Malfunction
• C1310 – Malfunction in HV System (Brake ECU seeing a hybrid fault)
• C2121 – No Signal from Transmitter ID1 (TPMS/Tire pressure sensor)

🔵 Body & Electrical

• B1421 – Solar Sensor Circuit (Passenger side; often triggers if in shade)
• B1423 – Pressure Switch Abnormal (A/C refrigerant low)
• B2799 – Engine Immobilizer System Malfunction (Key fob sync issue)