Motor Electronics Coolant Temperature Sensor Circuit Range/Performance

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
• CommonMotor electronics coolant pump not circulating
• CommonAir lock in the loop after a coolant change
• PossibleBlocked or debris-packed inverter radiator

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

1. 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.
2. Check the 12 volt battery first - it is the most common cause of scattered hybrid system codes.
3. 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.
4. Inspect the connector for corrosion and check the reference voltage and earth at the sensor.
5. Do not disturb anything orange.
6. Check that the electronics coolant pump actually runs. A loop that is not circulating gives a sensor reading that never changes, and the sensor is innocent.
7. Bleed the loop if coolant has been changed recently. An air lock at the sensor produces exactly this and is easy to overlook.