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

Coolant temperature sensor controls signal voltage to the ECM. The ECM applies voltage on circuit No. D12 to the sensor. When engine is cold, sensor resistance is high and ECM will see a high signal voltage. As engine warms, sensor resistance decreases 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 the ECM. Coolant temperature is one of the inputs used to control fuel delivery, Electronic Spark Timing (EST) and Idle Air Control (IAC).

1. Code 14A will set if engine has been running for at least 3 minutes and signal voltage indicates a coolant temperature greater than 302°F (150°C).
2. This simulates conditions for Code 14B. If ECM recognizes open circuit (high voltage), and displays low temperature, ECM and wiring are okay.