Code 14, Coolant Temperature Sensor (Temperature Too High): Notes

The coolant temperature sensor uses a thermistor to control signal voltage to ECM. The ECM supplies voltage on circuit No. 410 to sensor. When engine is cold, the sensor resistance is high, and ECM receives a high voltage signal.

As engine coolant warms, sensor resistance becomes less, and voltage signal drops. At normal engine operating temperature, voltage will measure about 1.5-2.0 volts at ECM terminal C10.

Coolant temperature is one of the inputs used to control:

Fuel delivery.
Electronic Spark Timing (EST).
Radiator cooling fan.
Torque Converter Clutch (TCC).
Idle Air Control (IAC).

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1) Check if code will set as a result of hard failure or intermittent condition. Code 14 will set if CTS signal voltage indicates a coolant temperature greater than 275°F (135°C) for 2 seconds.

Test Number 2) This test simulates conditions for a Code 15. If ECM recognizes an open circuit (high voltage), and displays a low temperature, the ECM and wiring are okay.