The coolant temperature sensor in an automobile is responsible for relaying engine temperature by measuring the temperature of engine coolant to the car's on-board computer. When this sensor malfunctions the symptoms range from poor engine performance to diminished fuel economy and engine shutdown. A driver that notices these symptoms early can isolate repair costs to the coolant sensor and prevent further damage to engine components.
Rich Running Engine
A failing coolant temperature sensor will prevent a vehicle's engine from entering a closed loop. This will cause the vehicle to run rich meaning the engine's fuel mixture will have a higher percentage of fuel to air which will result in diminished fuel economy. The driver will experience this as sluggish acceleration and having to ride the accelerator in order to achieve what would normally be an easily attainable city driving speed.
Increased Vehicle Emissions
As a result of a fuel-rich mixture entering the engine block, carbon monoxide emissions will also increase. The driver will notice black smoke coming from the vehicle's tail pipe, which will be more pronounced as the car is accelerating. This increase in carbon monoxide could also lead to engine sputtering which will cause the vehicle to stall while idling or attempting to accelerate from the idling position.
a malfunctioning temperature sensor will often send incorrect information to the vehicle's on-board computer. As a result, when the vehicle reaches a normal operating speed the sensor may relay an incorrect signal to the computer that the engine is overheating resulting in engine shutdown. The vehicle will not be able to start again until the engine has completely cooled and will need to have the sensor replaced in order to prevent the recurrence of the problem.