P0A00
Motor Electronics Coolant Temperature Sensor Circuit
- Severity
- Medium
- Driving
- Drive only to a garage
A fault in the motor electronics coolant temperature sensor circuit. Hybrids and electric vehicles have a second cooling loop, separate from the engine's, that cools the inverter and the motor electronics. It has its own pump, its own radiator and often its own reservoir - and topping up the engine coolant does nothing for it. The module uses this sensor to know whether the inverter is within its safe temperature range; without a reading it cannot confirm that, so it reduces power rather than risk cooking electronics it cannot see the temperature of.
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.
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.