Check DTC Codes for a Bad Coolant Temperature Sensor
If you scan your vehicle’s check engine light and come across any of the listed codes, it is possible that your coolant temperature sensor is faulty.
P0115 Engine Coolant Temperature Circuit Malfunction
This particular code indicates that the engine control unit (ECU) has detected an abnormal signal from the coolant temperature sensor. This issue could be due to a poor ground connection or faulty wiring.
P0116 Engine Coolant Temperature Circuit Range/Performance Problem
The P0116 code signifies that the values provided to the ECU by the coolant temperature sensor do not align with the expected range. Essentially, the sensor’s resistance may remain constant regardless of whether the engine is cold or warm.
To troubleshoot this problem, use a multimeter to measure the resistance in the coolant temperature sensor both when the engine is cold and when it has reached operating temperature. Remember to keep the sensor inside the engine block during this process, but ensure that the connector to the sensor is disconnected.
If the resistance varies as anticipated, there may be a faulty connection at the ECU. If the resistance remains constant, it is probable that the coolant temperature sensor is faulty.
P0117 Engine Coolant Temperature Circuit Low Input
P0117 signifies that the ECU has identified an abnormally extended period of low voltage from the coolant temperature sensor. For example, the voltage may register below 0.1 volts for 2.5 seconds or more.
P0118 Engine Coolant Temperature Circuit High Input
P0118 indicates that the ECU has identified an abnormally extended period of high voltage. For example, the coolant temperature sensor may read above 4.9 volts for 2.5 seconds or more.
The P0119 trouble code indicates that the engine coolant temperature sensor is sending an inconsistent signal, which is not normal. It takes time for the coolant to heat up, so if the sensor is sending a voltage that fluctuates between 1 and 4 volts multiple times per second, this is a clear indication of a faulty signal.
A faulty signal can be caused by electrical issues such as a poor ground connection or worn insulation within the wiring harness.
A closed thermostat keeps the coolant inside the engine block for a longer period, allowing it to retain some heat. Engines do not run efficiently when they are too cold.