Code 14, Coolant Temperature Sensor (Cts) Circuit High Temperature Indicated

The coolant temperature sensor uses a thermistor to control signal voltage to the ECM. The ECM applies voltage on Light Green/Black wire to the sensor. When engine is cold, thermistor resistance is high. This means the ECM will see high signal voltage. As engine warms, thermistor resistance is less. This means the ECM will see low signal voltage. When engine reaches normal operating temperature, signal voltage will be approximately 2.5-3.0 volts at ECM terminal No. 17. Coolant temperature is an input used by the ECM to control "Open Loop" timing, fuel delivery and early fuel evaporation.

1. This checks if code was set as the result of a hard failure or an intermittent condition. Code 14 will set if signal voltage indicates a coolant temperature more than 365°F (185°C) for 2 minutes.
2. This simulates conditions for Code 15. If ECM sees open circuit (high voltage) and displays low coolant temperature, the ECM and wiring are okay.