Wiring fault in fan 2 control circuit, such as chafing, short to earth or open circuit; Corroded, loose or damaged connector at the fan or control unit; Faulty battery cooling fan 2 motor or its internal driver electronics; Faulty fan control relay or fan speed controller, where fitted; Blown fuse or low supply voltage to the fan circuit from a weak 12 V battery; Fault inside the battery management or hybrid control unit; Water ingress or blocked ducting causing fan or connector damage.

P0A99

Hybrid/EV Battery Pack Cooling Fan 2 Control 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
99: FaultThe specific fault in that area

What it means

P0A99 is a generic powertrain code meaning the hybrid/EV battery management or powertrain control unit has detected a low voltage or low signal on the control circuit for battery pack cooling fan 2. The control unit commands the fan and monitors the circuit, and it saw a state that did not match the command, such as a circuit held low, shorted to earth or open. Exact fan numbering, location and control method (relay, direct drive or PWM signal) depend on the vehicle model.

Symptoms

Hybrid system or check engine warning light on
Battery cooling fan not running, or running constantly at full speed
Reduced hybrid or EV power output or limited charging and regeneration
Battery pack temperature rising on hot days or under heavy load
Unusual fan noise from the battery vent area
Possible additional battery temperature or fan related codes stored

Possible causes

Wiring fault in fan 2 control circuit, such as chafing, short to earth or open circuitlikely
Corroded, loose or damaged connector at the fan or control unitlikely
Faulty battery cooling fan 2 motor or its internal driver electronicslikely
Faulty fan control relay or fan speed controller, where fittedpossible
Blown fuse or low supply voltage to the fan circuit from a weak 12 V batterypossible
Fault inside the battery management or hybrid control unitrare
Water ingress or blocked ducting causing fan or connector damagerare

How to diagnose

Read all stored codes and freeze frame data, noting battery temperatures, vehicle state and whether other fan or temperature codes are present
Check the 12 V battery condition and charging voltage, as low supply can set control circuit faults
Inspect the battery cooling fan 2 intake and duct for blockage, debris or damage, following the manufacturer's safety procedure for high voltage components
Visually inspect the fan 2 wiring and connectors for chafing, corrosion, moisture and poor pin tension
Check the relevant fuse and relay, where fitted, against the manufacturer's wiring diagram
Using a bidirectional test function, command fan 2 on and off and listen and observe its response and any control signal change
Measure supply, earth and control signal at the fan connector against the wiring diagram to separate a wiring fault from a faulty fan
Check for a manufacturer calibration or software update relating to this code for the specific model

How to fix

Repair or replace damaged wiring and ensure the circuit is properly routed and secured
Clean, repair or replace corroded or damaged connectors
Replace the battery cooling fan 2 assembly if it fails testing
Replace a faulty relay, fuse or fan controller, and trace the cause if a fuse has blown
Restore 12 V battery and charging system health if supply voltage was low
Clear blocked ducts, then clear the code and confirm the fan operates and the fault does not return

Can I keep driving?

Medium severity

Short, gentle journeys are usually possible, but without proper cooling the battery may overheat and the car may limit power. Get it checked soon and avoid heavy loads or hot conditions until it is fixed.

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