P0AC5
Hybrid/EV Battery Temperature Sensor B Circuit.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- A
- AreaHybrid propulsion
- C5
- FaultThe specific fault in that area
What it means
P0AC5 means the hybrid or EV control unit has found a fault in the circuit of high-voltage battery temperature sensor B. The sensor's signal was outside the expected range, implausible against the other battery temperature sensors, or missing. Without reliable temperature data the system cannot manage battery cooling, charging and power limits properly. Which sensor is 'B' and where it sits depends on the model and battery design.
Symptoms
- Hybrid or EV system warning light, or a malfunction indicator lamp, on the dashboard
- Reduced power or limited acceleration (limp mode)
- Reduced regenerative braking or charging
- Battery cooling fan running constantly, or not running at all
- Poor fuel economy on a hybrid because the engine runs more to protect the battery
- Reduced electric-only range or the car refusing to charge
Possible causes
- Faulty battery temperature sensor B (open circuit, short circuit or drifted reading)likely
- Damaged, chafed or corroded wiring between the sensor and the battery management unitlikely
- Loose, corroded or contaminated connector at the sensor or battery packlikely
- Fault in the battery management unit's sensor input circuitpossible
- Moisture or coolant ingress into the battery pack harness or sensorpossible
- Real battery temperature problem, such as a blocked cooling duct or failed cooling fan, causing an implausible readingpossible
- Outdated control unit software that is a known cause of false sensor faults on some modelsrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting battery temperatures, state of charge and whether other battery codes are present
- Check the manufacturer's service information for the location and wiring of sensor B on this model and battery type
- Compare live data from all battery temperature sensors on a cool car; they should read similar values, and sensor B should not be fixed at an extreme value or stuck
- Inspect the battery cooling air intake, ducts, filters and fan for blockage, debris or damage
- Visually inspect accessible wiring and connectors for chafing, corrosion, water ingress or loose pins, following high-voltage safety procedures
- Test the sensor circuit for continuity, short to earth or short to supply, and sensor resistance against the specified values, with the high-voltage system isolated by a trained technician
- Wiggle-test the harness while watching live data to find intermittent faults
- If wiring and sensor test good, check for software updates and for faults in the battery management unit
How to fix
- Replace the faulty battery temperature sensor or sensor assembly as specified for the model
- Repair or replace damaged wiring and terminals in the sensor circuit
- Clean, secure or replace corroded or loose connectors, and fix the source of any moisture ingress
- Clear blocked cooling ducts or repair the battery cooling fan so temperatures read correctly
- Update the control unit software if the manufacturer lists it as the fix for this fault, or replace the battery management unit if it is proven faulty
- Clear the code after the repair and road test to confirm it does not return
Can I keep driving?
The car can usually be driven for a short time, but battery protection may be reduced, so avoid hard driving and long trips and have it diagnosed soon. If the car is overheating, smells unusual or goes into severe limp mode, stop driving and seek help. All work on the high-voltage system must be done by a suitably trained technician.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.