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

The coolant temperature sensor uses a thermistor to control signal voltage to ECM. The ECM applies a reference voltage on signal wire to sensor. When engine is cold, sensor resistance is high, and ECM receives a high signal voltage.

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 by ECU to control the following.

• 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.

1. This step determines whether code is caused by a hard failure or intermittent condition. Code 14 will set if CTS signal voltage indicates coolant temperature is greater than 275°F (135°C) for 3 seconds.
2. This step 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.