Code 14B, Coolant Temperature Sensor (Cts) Circuit Low 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 No. A11. Coolant temperature is an input used by the ECM to control fuel delivery, Engine Spark Timing (EST) and engine idle speed.

1. This checks if code was set as the result of a hard failure or an intermittent condition. Code 14B sets if signal voltage indicates a coolant temperature less than -22°F (-30°C) after engine has been running for 2 minutes.
2. This simulates conditions for Code 14A. If ECM sees grounded circuit (low voltage) and displays high coolant temperature, the ECM and wiring are okay.
3. This determines if wiring or ECM is faulty.