P0AC6
Hybrid/EV Battery Temperature Sensor B Circuit Range/Performance.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- A
- AreaHybrid propulsion
- C6
- FaultThe specific fault in that area
What it means
P0AC6 means the hybrid or EV battery control unit has judged the signal from hybrid/EV battery temperature sensor 'B' to be implausible, although the circuit is not necessarily open or shorted. The reading may be stuck, drift too slowly or quickly, or disagree with other battery temperature sensors or the expected temperature after a cold soak. Sensor location and the plausibility test vary by model and battery design.
Symptoms
- Hybrid or EV system warning light on the dashboard
- Reduced power, limited electric assist or reduced regenerative braking
- Battery cooling fan running constantly, erratically or not at all
- Reduced electric-only range or altered charging behaviour
- Poor fuel economy as the system relies more on the engine
Possible causes
- Faulty battery temperature sensor B giving a stuck or drifting readinglikely
- Corroded, loose or damaged connector terminals at the sensor or battery control unitlikely
- Damaged wiring or high resistance in the sensor signal or ground circuitpossible
- Restricted battery cooling airflow (blocked intake, ducting or fan fault) causing real temperature differences between modulespossible
- Fault in the battery control unit's sensor input circuitrare
- Outdated control unit software where the manufacturer has a known fix for the plausibility testrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting battery temperatures, ambient temperature and vehicle state when the code set.
- Check for related codes for other battery temperature sensors, cooling fan or battery control unit faults, and deal with those first.
- Following the manufacturer's high-voltage safety procedure, which only suitably trained staff should do, visually inspect the sensor wiring, connectors and battery cooling ducts for damage, moisture, debris or blockage.
- After the car has sat cold for several hours, compare live data from all battery temperature sensors and check that they read close to each other and to ambient.
- Watch sensor B live data while the system warms up or the cooling fan runs, and check that it responds smoothly and in step with the others.
- Check the sensor resistance and the circuit's reference voltage, signal and ground against the manufacturer's specification, including wiggle-testing the harness.
- Check that the battery cooling fan and airflow work correctly, as real temperature spread can look like a sensor fault.
- Look for manufacturer service bulletins or software updates relating to this code for the specific model.
How to fix
- Replace the faulty battery temperature sensor or sensor assembly as the manufacturer specifies.
- Clean, repair or replace corroded or damaged connectors and terminals.
- Repair or replace damaged wiring in the sensor signal or ground circuit.
- Clear blocked battery cooling ducts or intakes and repair any faulty cooling fan.
- Update the battery control unit software if an outdated version is a known cause, or replace the unit if it is confirmed faulty.
Can I keep driving?
The car can usually be driven for a short time, but expect reduced hybrid or EV performance, and the battery's temperature monitoring is compromised. Have it diagnosed soon, and stop driving if the system warns of overheating or the car goes into limp mode.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.