P0A9C

What it means

P0A9C is the generic code for a range or performance fault in the hybrid or EV battery temperature sensor 'A' circuit. The battery control unit compared the reading from this sensor with what it expected, based on other battery temperature sensors, coolant or ambient temperature and the time since the car was last used, and found it implausible. The sensor signal is still within electrical limits, so the fault is usually a drifting sensor, a poor connection or a real temperature difference in the pack.

Symptoms

• Hybrid or EV system warning light on, often with the malfunction indicator lamp
• Reduced power or limited acceleration
• Battery cooling fan running louder or more often than normal
• Reduced electric-only driving or charging rate
• Poor or fluctuating state-of-charge readings
• In some cases no symptoms other than the warning light

Possible causes

• Faulty or drifting battery temperature sensor 'A' (reads out of step with the other pack sensors)likely
• Corroded, loose or damaged connector terminals at the sensor or battery control unitlikely
• Damaged wiring to the sensor (chafing, high resistance or intermittent open circuit)possible
• Genuine uneven pack temperature caused by a blocked, failed or restricted battery cooling fan, duct or intakepossible
• Fault in the cooling or thermal management system, such as a coolant pump or valve fault on liquid-cooled packs (depends on model)possible
• Fault inside the battery control unit or its sensing circuitrare
• Internal battery module fault causing a local hot spotrare

How to diagnose

1. Read all stored codes and freeze frame data, noting battery temperatures, ambient temperature and vehicle state when the code set, and check for other battery or cooling codes.
2. Check for relevant technical service bulletins and software updates for the specific model, as sensor location and strategy vary.
3. Inspect the battery cooling intake, ducts, filters and fan for blockage, debris or damage, and check the fan runs.
4. Compare live data from all battery temperature sensors after the car has been cold-soaked; they should read close to each other and to ambient.
5. Inspect the sensor wiring and connectors for corrosion, bent pins, water ingress and chafing, following the high-voltage safety procedure.
6. Wiggle-test the harness while watching live temperature data for jumps or dropouts.
7. Measure sensor resistance and circuit voltage against the manufacturer's specification, and check for open circuit or high resistance.
8. Check the thermal management system operation on liquid-cooled packs, including coolant level and pump operation, as per the model procedure.

How to fix

• Replace the faulty battery temperature sensor or the sensor assembly, as the manufacturer specifies.
• Clean or repair the connector terminals, or replace the connector if damaged.
• Repair or replace damaged wiring in the sensor circuit.
• Clear blockages from the cooling intake and ducts, and replace a failed cooling fan or filter.
• Repair the thermal management fault, such as a pump, valve or coolant level issue.
• Replace or reprogram the battery control unit only if testing confirms it is faulty or the manufacturer lists a calibration update for this fault.

Can I keep driving?

Nearby codes

• P0A9BGenericHybrid/EV Battery Temperature Sensor A Circuit
• P0A9DGenericHybrid/EV Battery Temperature Sensor A Circuit Low