Code 14A - Cts Circuit (High Temperature Indicated): Notes

Coolant temperature sensor uses a thermistor to control signal voltage to the ECM. The ECM applies voltage on Gray/Black wire to the sensor. When engine is cold, thermistor resistance is high and ECM will see a high signal voltage.

As engine warms, thermistor resistance is less and ECM will see a 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, Electronic Spark Control (EST), idle speed and cooling fan.

1. This determines if code set because of a hard failure or an intermittent condition. Code 14A sets if signal voltage indicates a coolant temperature greater than 275°F (135°C) for 255 seconds.
2. This simulates conditions for Code 14B. If ECM sees open circuit (high voltage) and displays low coolant temperature, ECM and wiring are okay.