Code 14, Coolant Temp Sensor (Cts) CKT High Temp Indicated: Notes

CTS uses a thermistor to control signal voltage to ECM. ECM applies voltage on Gray/Black wire to sensor. When engine is cold, thermistor resistance is high. Thus, ECM will sense high signal voltage.

As engine warms up, thermistor resistance decreases and ECM senses low signal voltage. When engine reaches normal operating temperature, signal voltage will be approximately 1.5-2.0 volts at ECM terminal C10. Coolant temperature is one of the inputs used by ECM to control fuel delivery, Electronic Spark Control (EST) and Idle Air Control (IAC).

1. This checks if code is due to a hard failure or intermittent condition. Code 14 is set if signal voltage indicates coolant temperature is greater than 275°F (135°C) for 3 seconds.
2. This simulates conditions for Code 14 (low temperature indicated). If ECM senses open circuit (high voltage) and displays low coolant temperature, ECM and wiring are okay.