P0AE9
Hybrid/EV Battery Temperature Sensor D Circuit Range/Performance.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- A
- AreaHybrid propulsion
- E9
- FaultThe specific fault in that area
What it means
P0AE9 means the hybrid or EV control unit has found that the signal from traction battery temperature sensor 'D' is implausible. It is not necessarily open or shorted, but it does not match what is expected. The control unit usually compares it with the other battery temperature sensors, the intake air temperature or the temperature after a long soak. Which physical sensor is 'D' depends on the model and pack design.
Symptoms
- Hybrid or EV system warning light on, often with the main warning light
- Reduced power or limited electric assist
- Battery cooling fan running loudly or constantly
- Reduced charging or regeneration, or reduced electric-only driving
- Poor fuel economy because the engine runs more to protect the battery
- Charging slower than normal or not starting (plug-in and EV models)
Possible causes
- Faulty or drifting battery temperature sensor Dlikely
- Damaged wiring, corrosion or poor connection at the sensor or battery monitoring connectorlikely
- Blocked or failed battery cooling fan, duct or air filter causing a real temperature difference between sensorspossible
- Fault in the coolant circuit on liquid-cooled packs (low coolant, air in the system, pump fault)possible
- Fault in the battery monitoring unit or battery control modulerare
- Internal pack fault causing a genuine local hot or cold spotrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting battery temperatures, ambient temperature and vehicle state when the code set.
- Check for related codes for other battery temperature sensors, the cooling fan or the battery monitoring unit, and deal with those first.
- Compare live data from all battery temperature sensors after the car has been cold-soaked. Sensors should read close to each other and to ambient. Note any sensor that is fixed, jumping or far off.
- Inspect the battery cooling air intake, ducts, filter and fan for blockage, debris or damage, and check the fan runs when commanded.
- On liquid-cooled systems, check coolant level, condition and pump operation according to the manufacturer's procedure.
- Inspect the wiring and connectors between the sensor and the battery monitoring unit for corrosion, pin tension, chafing and moisture. Only do this after following the high-voltage isolation procedure.
- Check the sensor resistance and the reference voltage and signal circuit against model-specific data.
- Check for software updates or technical bulletins for the model if no hardware fault is found.
How to fix
- Replace the faulty battery temperature sensor or the sensor harness section.
- Repair or replace damaged wiring and connectors, and clean or reseat corroded terminals.
- Clear blockages and replace the cooling fan, filter or ducting if faulty.
- Restore the correct coolant level, bleed the system and repair pump or circuit faults on liquid-cooled packs.
- Replace or reprogram the battery monitoring unit only after the sensor and wiring have been proved good, and apply any manufacturer calibration update if it is a known cause.
Can I keep driving?
The car may be driven for a short time, but power may be limited and the battery will not be protected as well as it should be. Get it checked soon, and stop if there are overheating warnings, a burning smell or a loss of drive. Work on high-voltage components must only be done by trained staff.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.