Open circuit or high resistance in the sensor signal or return wiring; Corroded, loose or damaged connector at the sensor or battery control unit; Faulty battery pack air temperature sensor (internal open circuit); Signal wire shorted to a voltage supply; Blocked or restricted battery cooling air intake or duct affecting the sensor reading; Fault in the battery control unit or its sensor reference supply.

P0AAF

Hybrid/EV Battery Pack Air Temperature Sensor A Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

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

What it means

P0AAF means the hybrid or EV control unit has seen a signal from the battery pack air temperature sensor A circuit that is higher than the expected range. This usually points to an electrical fault such as an open circuit or short to voltage, which makes the sensor read extremely cold, rather than a genuinely hot pack. The exact sensor location and how the reading is used for cooling control vary by model.

Symptoms

Hybrid or EV system warning light on
Malfunction indicator lamp on
Battery cooling fan running constantly or not at all
Reduced power or limited hybrid or EV assist
Reduced charging or regeneration
Battery temperature reading stuck at an implausible low value on a scan tool

Possible causes

Open circuit or high resistance in the sensor signal or return wiringlikely
Corroded, loose or damaged connector at the sensor or battery control unitlikely
Faulty battery pack air temperature sensor (internal open circuit)likely
Signal wire shorted to a voltage supplypossible
Blocked or restricted battery cooling air intake or duct affecting the sensor readingrare
Fault in the battery control unit or its sensor reference supplyrare

How to diagnose

Read all stored and pending codes and note freeze frame data, including battery temperatures and ignition status.
Check for related codes on other battery temperature sensors or the sensor reference supply, as these point to a shared circuit fault.
Compare the live data for sensor A with the other pack temperature sensors and with ambient temperature; an implausibly low or fixed value suggests an electrical fault.
Visually inspect the sensor wiring and connectors for damage, water ingress, corrosion, pushed-out pins or chafing, following the manufacturer's high-voltage safety procedure.
Check that the cooling air intake, ducts and filter are clear, as listed in the model's service information.
With the system safely isolated, measure the sensor resistance and compare it with the manufacturer's specification at the current temperature.
Check the signal circuit for continuity, short to voltage and short to earth, and check the reference voltage at the connector.
Clear the codes and retest to see if the fault returns, after repairs are done.

How to fix

Repair or replace damaged wiring in the sensor circuit.
Clean, repair or replace corroded or damaged connectors and terminals.
Replace the battery pack air temperature sensor if its resistance is out of specification.
Clear any blockage in the battery cooling air intake or ducting.
Have the battery control unit tested and replaced or reprogrammed only if the circuit checks prove it to be at fault and the manufacturer specifies it.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but the system may lose accurate battery temperature monitoring and could limit power or cooling. Have it diagnosed soon, and stop driving if warnings escalate or the car loses power. Work on the high-voltage system should only be done by a suitably trained person.

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