The engine coolant sensor monitors the operating temperature of the engine on an automobile and sends information to the onboard computer. The computer makes adjustments that ensure the vehicle reaches and maintains the ideal operating temperature, according to Auto Parts Warehouse. The monitor is the brain of the cooling system.
When the vehicle starts in the morning, the engine is cold and needs to reach the ideal operating temperature for maximum fuel economy. The monitor provides information to the computer to close emissions ports so the engine warms quickly, according to Auto Parts Warehouse. Once the engine warms, the information provided sends a signal to open these ports for cleaner operation of the vehicle. In order to prevent overheating, the monitor is responsible for starting the cooling fan, which pulls air through the radiator when the car is moving slowly or idling.
If there is a problem with the engine coolant monitor, the diagnostic computer returns an error code, causing the check-engine light to illuminate, according to RepairPal. A mechanic uses a scan tool to retrieve the diagnostic code. The faulty monitor sometimes causes difficulty in starting the engine and reduces fuel economy. Other problems that sometimes cause a faulty coolant-monitor code include problems with the engine coolant, wiring, thermostat or overheating.