P0A02
Motor Electronics Coolant Temperature Sensor Circuit Low
- Severity
- Medium
- Driving
- Drive only to a garage
The motor electronics coolant temperature signal is reading low - typically a short to earth or an open circuit, rather than a genuine temperature. Note that on these sensors the electrical direction and the temperature direction are opposite: resistance falls as temperature rises, so a short reports impossibly hot coolant and an open circuit reports impossibly cold.
Possible causes
- CommonFailed coolant temperature sensor
- CommonCorroded or damaged connector
- CommonWiring fault between the sensor and the module
- CommonLow coolant level in the motor electronics loop - a reservoir people forget exists
- PossibleLoss of reference voltage or earth
- PossibleLow 12 volt battery voltage
What you might notice
- Reduced power, especially after sustained hard driving or a long climb
- Hybrid or electric drive system warning message
- Cooling fans running constantly
- Reduced charging rate
- Check engine light on
What to check, in order
- Check the level in the motor electronics coolant reservoir, which is separate from the engine's. This is the single most missed check on these vehicles - people top up the engine coolant, see a full bottle and move on.
- Check the 12 volt battery first - it is the most common cause of scattered hybrid system codes.
- Compare this reading against the other temperatures the module has after the vehicle has stood overnight. They should agree within a few degrees, and the odd one out is the faulty one.
- Inspect the connector for corrosion and check the reference voltage and earth at the sensor.
- Do not disturb anything orange.
- Unplug the sensor and see whether the low reading persists at the harness. That separates a wiring fault from a failed sensor in a couple of minutes.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx