P0AAC
Hybrid/EV Battery Pack Air Temperature Sensor A 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
- AC
- FaultThe specific fault in that area
What it means
P0AAC is the generic code for a fault in the circuit of hybrid or EV battery pack air temperature sensor A. The control unit that monitors the battery saw a signal from this sensor that was outside the expected range, or that did not make sense compared with other temperature readings. Exact sensor position and the way the fault is judged vary by model, so check the manufacturer data for the vehicle.
Symptoms
- Hybrid or battery system warning light on the dashboard
- Cooling fan for the battery running loudly or constantly
- Reduced power or the car going into a limited performance mode
- Reduced electric-only driving or poor charging and regeneration
- Battery temperature readings that look wrong or stuck on a scan tool
Possible causes
- Faulty battery pack air temperature sensor (open circuit, short circuit or drifted reading)likely
- Damaged, chafed or corroded wiring between the sensor and the battery control unitlikely
- Poor connection at the sensor or battery control unit connector, such as loose, bent or corroded terminalspossible
- Blocked battery cooling duct or filter causing real temperature differences that the unit judges as implausiblepossible
- Fault in the battery control unit sensor input or reference voltage supplyrare
- Outdated software in the battery control unit, where the manufacturer lists it as a known cause for the modelrare
How to diagnose
- Read all stored codes and freeze frame data, noting battery temperatures, ambient temperature and whether the fault is current or intermittent.
- Compare the reading from sensor A with the other battery temperature sensors and the intake air temperature on a scan tool after the car has been cool for some time; they should be close.
- Check for manufacturer service bulletins and software updates relevant to the model.
- Inspect the sensor, its wiring and connectors for damage, water ingress, corrosion or loose terminals, following the high-voltage safety procedure for the vehicle.
- Check the battery cooling intake, ducts, filter and fan for blockages or debris, as the layout depends on the model.
- With the system made safe, test the sensor resistance against the manufacturer's temperature specification.
- Test the sensor circuit for continuity, shorts to earth or supply, and correct reference voltage, using the wiring diagram for that model.
- Wiggle test the harness while watching the live temperature value to find intermittent faults.
How to fix
- Replace the battery pack air temperature sensor if its resistance or reading is out of specification.
- Repair or replace damaged wiring and renew faulty connectors or terminals.
- Clean and refit connectors and apply the correct protection against moisture where needed.
- Clear blocked cooling ducts or replace a dirty filter and confirm the fan works properly.
- Update the battery control unit software if an applicable update exists, or replace the unit if the fault is confirmed in it.
Can I keep driving?
The car can usually be driven for a short time, but fix it soon because the battery may not be cooled or protected properly and power may be limited. High-voltage work must only be done by someone trained to do it, and if the battery overheats or a stronger warning appears, stop driving and get help.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.