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

The coolant temperature sensor uses a thermistor to control signal voltage to the ECM. The ECM applies voltage on Gray wire to the sensor. When engine is cold, thermistor resistance is high. This means the ECM sees high signal voltage.

As engine warms, thermistor resistance is less. This means the ECM sees low signal voltage. When engine reaches normal operating temperature, signal voltage will be approximately 1.5-2.0 volts at ECM terminal A11. Coolant temperature is an input used by the ECM to control fuel delivery, Electronic Spark Control (EST) and Idle Air Control (IAC).

1. This checks if code was set by a hard failure or an intermittent condition. Code 14 sets if signal voltage indicates a coolant temperature more than 275°F (135°C) for 3 seconds.
2. This simulates conditions for Code 14A. If ECM sees open circuit (high voltage) and displays low coolant temperature, the ECM and wiring are okay.