Faulty battery temperature sensor 'C' reading out of range (internal short); Sensor signal wire shorted to earth in the battery harness; Damaged, corroded or loose connector at the sensor or battery monitoring module; Moisture or coolant ingress into the sensor circuit or connector; Fault in the battery monitoring module or battery control unit input circuit; Outdated control unit software where the manufacturer lists it as a known cause.

P0ACC

Hybrid/EV Battery Temperature Sensor C Circuit Low.

Generic
Powertrain
Generic code
Medium severity

How this code is built

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

What it means

P0ACC means the hybrid or EV control unit saw the signal from battery temperature sensor 'C' fall below the expected range. This usually means a sensor circuit voltage that is too low, such as a short to earth, a damaged sensor or a wiring fault. The control unit can no longer trust the pack temperature reading, so it may limit battery use to protect the pack. Which sensor is 'C' and where it sits depends on the model and battery design.

Symptoms

Hybrid or EV system warning light on, often with the malfunction indicator lamp
Reduced power or the car going into a limited performance mode
Reduced electric assist, or the engine running more often on a hybrid
Reduced charging speed or reduced regenerative braking
Battery cooling fan running constantly or at an odd speed
Reduced EV range or unusual battery state of charge readings

Possible causes

Faulty battery temperature sensor 'C' reading out of range (internal short)likely
Sensor signal wire shorted to earth in the battery harnesslikely
Damaged, corroded or loose connector at the sensor or battery monitoring modulepossible
Moisture or coolant ingress into the sensor circuit or connectorpossible
Fault in the battery monitoring module or battery control unit input circuitrare
Outdated control unit software where the manufacturer lists it as a known causerare

How to diagnose

Read all stored and pending codes and freeze frame data, noting whether other battery temperature or cooling codes are present
Check for manufacturer service bulletins and the model-specific location of temperature sensor C
Compare the live data for all battery temperature sensors against each other with the pack at rest and cold; a single sensor reading very low or implausible points to the circuit
Visually inspect accessible wiring, connectors and the battery cooling air path for damage, water, debris or corrosion
Have a qualified high-voltage technician isolate the system following the manufacturer's safe procedure before any work on the battery pack
Measure the sensor resistance and compare it with the specification for the model
Check the signal and reference wiring for shorts to earth and for continuity, and inspect the connector pins
Clear the code after repair and road test, confirming it does not return and that the temperature readings are plausible

How to fix

Replace the faulty battery temperature sensor 'C' using the manufacturer's procedure
Repair or replace the damaged wiring section causing the short to earth
Clean, repair or replace the affected connector and dry out any moisture, finding and fixing the source of the water
Replace the battery monitoring module or control unit only if testing proves the input circuit is faulty
Update the control unit software only where a known fault is confirmed in the manufacturer's information

Can I keep driving?

Medium severity

The car may be driveable, but expect reduced power and the system limiting battery use, and the fault may get worse. Book it in soon, and stop driving if warnings escalate, the car loses drive or there is any smell or heat from the battery. Work on the high-voltage system should only be done by a suitably qualified technician.

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