Toyota Prius Hybrid Battery Error Codes

Toyota Prius Hybrid Battery Diagnostic Codes

Hybrid vehicles are engineered for efficiency, but battery issues can trigger warning lights and error codes. This guide helps you understand the most common Toyota Prius codes and what actions to take.

If you notice warning lights, reduced fuel efficiency, or unusual behavior from your hybrid system, you can check the battery codes using an OBD-II scanner. Connect the scanner to your vehicle’s diagnostic port to read error codes and identify which component requires attention.

Critical Battery Replacement Codes

  • Possible Causes:

    • Service plug (safety disconnect) not fully locked in place

    • Loose or disconnected high-voltage wiring harness

    • Damaged or corroded interlock connectors

    • Faulty HV battery pack connection or inverter safety plug

    Solution:

    • Verify HV service plug is properly installed and locked

    • Inspect high-voltage harness and interlock connectors for damage/corrosion

    • Ensure battery pack and inverter connectors are secure

    • If problem persists, perform continuity test on interlock circuit and replace faulty component

  • Possible Causes: Worn battery cells

  • Solution: Replace battery pack or individual cells

  • We have a detailed post about this code

  • Possible Causes: Battery aging or capacity loss

  • Solution: Inspect and replace battery as needed

  • We have a detailed post about this code

Individual Cell / Module Codes

  • Possible Causes:

    • One or more battery modules showing abnormal voltage

    • Weak or failing cell(s) in HV battery pack

    • Corroded or loose module connections

    • Battery management system (BMS) error in monitoring individual modules

    Solution:

    • Inspect and clean module connections

    • Measure individual module voltages and identify weak/failing modules

    • Replace faulty module(s) if necessary

    • Clear codes after repair and allow BMS to rebalance

  • Possible Causes: Reduced capacity of certain cells

  • Solution: Replace affected cell or battery pack

  • We have a detailed post about this code

  • Possible Causes:

    • Faulty or degraded battery module “D”

    • Loose, corroded, or damaged module connectors

    • Poor contact between modules in the HV battery pack

    • Hybrid Battery ECU misreading voltage due to sensor or wiring issue

    • Module imbalance due to age or repeated cycling

    Solution:

    • Inspect module “D” and connectors for damage or corrosion

    • Test module voltage and replace if performance is below specification

    • Check inter-module connections and tighten/clean as needed

    • Inspect wiring and sensors related to module voltage

    • Replace Hybrid Battery ECU only if wiring and module are confirmed good but code persists

  • Possible Causes: Worn or damaged module

  • Solution: Inspect and replace module

Voltage & Temperature Related Codes

Possible Causes:

  • Faulty evaporator temperature sensor

  • Damaged or disconnected wiring

  • Short or open circuit in HVAC system

  • Poor sensor calibration or ECM/ECU fault

Solution:

  • Inspect sensor and wiring harness for damage or loose connections

  • Replace faulty evaporator temperature sensor

  • Check HVAC control module for proper operation

  • Clear code after repair and test system operation

  • Possible Causes: Weak or failing 12V battery

  • Solution: Check and replace 12V battery

Possible Causes:

  • Dirty or faulty MAF sensor

  • Intake air leaks

  • Damaged wiring or poor connection

  • ECU malfunction

Solution:

  • Clean or replace MAF sensor

  • Inspect intake hoses for leaks

  • Repair wiring or connectors if needed

  • Clear codes and test drive

Possible Causes: Faulty or clogged cooling fan, damaged wiring/connectors, or malfunction of Battery ECU.

Solution: Clean or replace cooling fan, inspect and repair wiring/connectors, check Battery ECU if issue persists.

Possible Causes:

  • Low or leaking hybrid battery coolant level

  • Blocked or restricted coolant flow in battery pack

  • Faulty coolant pump or thermostat

  • Faulty temperature sensors or wiring

Solution:

  • Check coolant level and top up if needed

  • Inspect hoses and connectors for leaks or blockages

  • Test coolant pump operation and replace if defective

  • Inspect temperature sensors and wiring; replace if necessary

  • Clear code after system check and refill/rebalance coolant

  • Possible Causes: Faulty battery or wiring issue

  • Solution: Inspect battery and connections

  • Possible Causes:

    • Faulty hybrid battery current sensor

    • Damaged or loose wiring/connectors

    • Poor ground connection

    • Hybrid Battery ECU internal fault

    Solution:

    • Inspect and repair wiring/connectors

    • Clean or tighten ground points

    • Replace current sensor if faulty

    • Diagnose/replace Hybrid Battery ECU if necessary

  • Possible Causes:

    • Faulty hybrid battery current sensor sending too high signal

    • Short to power in the sensor wiring

    • Corrosion or poor contact causing incorrect readings

    • Hybrid Battery ECU fault

    Solution:

    • Check wiring for shorts and repair if needed

    • Clean and secure connector terminals

    • Replace current sensor if defective

    • Test/replace Hybrid Battery ECU if issue persists

  • Possible Causes:

    • Power supply overvoltage to Hybrid Battery ECU (BECM)

    • Damaged wiring harness or short to power

    • Internal failure in Battery ECU

    • Incorrect replacement battery/ECU installation

    Solution:

    • Inspect power supply wiring for shorts or damage

    • Verify proper voltage levels to BECM

    • Replace Battery ECU if faulty

    • Clear codes and recheck system operation

  • Possible Causes: Faulty sensor or overheating

  • Solution: Check sensors and cooling system

Hybrid System & Inverter Codes

Possible Causes:

  • ABS ECU error

  • Low brake fluid or hydraulic system issue

  • Wiring or connector problem

  • Faulty wheel speed sensor

Solution:

  • Inspect ABS ECU and wiring

  • Check brake fluid and hydraulic components

  • Replace faulty sensors

  • Clear codes and test drive

Possible Causes:

  • Faulty wheel speed sensor

  • Damaged sensor wiring or connector

  • Debris or corrosion at sensor hub

  • Faulty ABS module

Solution:

  • Inspect and clean wheel speed sensor and hub

  • Test sensor and replace if faulty

  • Repair damaged wiring or connectors

  • Check ABS module if sensor replacement does not resolve code

Possible Causes:

  • Faulty brake pressure sensor or brake booster

  • Malfunctioning ABS/ESC module

  • Low brake fluid level

  • Air in brake lines or contaminated brake fluid

  • Wiring issues or poor electrical connections in brake system

Solution:

  • Inspect and replace faulty brake pressure sensor or booster if needed

  • Check and repair ABS/ESC module wiring and connections

  • Ensure brake fluid is at proper level and replace if contaminated

  • Bleed air from brake lines

  • Replace ABS/ESC module if it is defective after other checks

Possible Causes:

  • Faulty rear left wheel speed sensor

  • Damaged sensor wiring or connector

  • ABS module malfunction

Solution:

  • Inspect and replace faulty wheel speed sensor

  • Repair wiring or connector

  • Clear codes and test drive

Possible Causes:

  • TCS disabled due to previous ABS or wheel sensor faults

  • Faulty traction control module

  • Low brake fluid level affecting TCS

  • Faulty yaw rate or steering angle sensor

Solution:

  • Resolve any ABS/wheel sensor codes (like C1236) first

  • Check brake fluid level and top up if needed

  • Inspect TCS module and related sensors

  • Replace defective modules or sensors if required

Possible Causes:

  • Faulty oxygen sensor heater (Bank 1, Sensor 1)

  • Blown fuse or damaged wiring in HO2S circuit

  • Poor connection at sensor connector

  • ECU malfunction

Solution:

  • Inspect and replace faulty HO2S sensor

  • Check wiring harness and fuses; repair as needed

  • Ensure secure sensor connector

  • Clear codes after repair and test drive

Possible Causes:

  • Faulty oxygen sensor heater (Bank 1, Sensor 2)

  • Blown fuse or damaged wiring

  • Poor connector connection

  • ECU issue

Solution:

  • Replace faulty HO2S sensor

  • Inspect wiring and fuses

  • Secure connectors

  • Clear codes and test drive

Possible Causes:

  • Faulty EGR solenoid or valve

  • Damaged wiring or connector in EGR circuit

  • ECU issue

Solution:

  • Inspect and replace EGR solenoid/valve if needed

  • Repair wiring and connectors

  • Clear codes and test drive

Possible Causes:

  • Failing catalytic converter

  • Faulty upstream/downstream oxygen sensors

  • Exhaust leaks

  • Wiring issues

Solution:

  • Inspect catalytic converter and replace if needed

  • Check and replace oxygen sensors

  • Repair exhaust leaks

  • Clear codes and test drive

  • Possible Causes: Battery, inverter, or system issue

  • Solution: Diagnose and repair specific component

Possible Causes:

  • Dirty or faulty throttle body

  • Clogged fuel filter or weak fuel pump

  • Low-quality fuel or clogged injectors

  • Faulty MAF/MAP sensor

  • Ignition issues (spark plugs, coils)

  • Engine compression problems

Solution:

  • Inspect and clean the throttle body

  • Check fuel pressure, replace fuel filter/pump if needed

  • Use high-quality fuel, clean or replace injectors if necessary

  • Diagnose and replace MAF/MAP sensor if required

  • Replace worn spark plugs/coils

  • Perform a compression test and repair the engine if needed

Possible Causes:

  • Dirty or stuck throttle body

  • Faulty Mass Air Flow (MAF) sensor or intake air leak

  • Weak or failing fuel pump / clogged fuel filter

  • Worn spark plugs or weak ignition coil

  • ECU software issue or hybrid system not enabling fuel/ignition properly

Solution:

  • Clean and inspect throttle body

  • Check MAF sensor and intake hoses for leaks

  • Measure fuel pressure and replace pump/filter if needed

  • Replace spark plugs or ignition components if worn

  • Update/reprogram ECU if applicable and clear stored codes

Possible Causes:

  • Fuel system malfunction (fuel not reaching cylinders)

  • Ignition system problems

  • Discharged or faulty HV battery (engine won’t crank)

  • Starter/inverter issues that crank the ICE

  • Faulty crankshaft or camshaft position sensor

  • Fuel freezing/low temperature (common in winter)

Solution:

  • Check fuel level and quality, and fuel system pressure

  • Inspect spark plugs and coils, replace if necessary

  • Ensure HV battery is charged (and no other battery codes present)

  • Diagnose the inverter and engine starting system

  • Check CKP/CMP sensors (crankshaft/camshaft)

  • In cold weather – use engine heater or winter-grade fuel

  • Possible Causes: Damaged connectors or wiring

  • Solution: Check and repair high-voltage connections

Possible Causes:

  • Faulty HV battery current sensor

  • Poor connection or corrosion at the sensor connector

  • Damaged or shorted wiring between the sensor and HV ECU

  • Malfunctioning HV Battery ECU (controller)

  • Rarely – battery internal issue causing abnormal current flow

Solution:

  • Inspect wiring and connectors related to the HV battery current sensor

  • Test the current sensor for proper resistance and voltage output

  • Clean and restore all electrical contacts

  • Replace the HV battery current sensor if defective

  • If ECU-related issue is suspected, check for software updates or replace the HV Battery ECU

  • Possible Causes: Inverter or battery issues

  • Solution: Inspect inverter and battery

Possible Causes:

  • Faulty ABS control module

  • Damaged or disconnected wiring/connectors in the CAN network

  • Blown fuse related to ABS module

  • Intermittent communication issues due to ECU problems

Solution:

  • Inspect ABS module and wiring harness for damage

  • Check and replace any blown fuses

  • Reconnect or repair loose/disconnected connectors

  • Replace ABS control module if faulty

Possible Causes:

  • Faulty BCM

  • Broken or loose wiring in CAN bus

  • Poor ground connections

  • Other ECU causing communication interference

Solution:

  • Inspect BCM wiring and connectors

  • Ensure proper grounding of BCM

  • Scan other ECUs for faults that may block communication

  • Replace BCM if found defective

How do I know if my Prius battery needs replacement?
Check for warning lights, reduced efficiency, or unusual behavior. Use an OBD-II scanner to read battery error codes.

Can I fix individual Prius battery cells myself?
Replacing individual cells is possible but risky due to high voltage. It’s recommended to consult a certified hybrid technician.

If your Prius shows a check engine light, scan for hybrid battery codes. Diagnostic trouble codes can reveal issues with battery modules, the high voltage battery, or the high voltage system. Common codes include P0A80 replace hybrid battery pack, P0A85 battery cooling fan, P0A93 inverter cooling system, and P3030 high voltage line snapped. Proper servicing hybrid batteries keeps your vehicle safe and running efficiently.