Code 15, Coolant Temperature Sensor (Cts) Circuit High Temperature Indicated

The coolant temperature sensor uses a thermistor to control signal voltage to the ECM. The ECM applies voltage on circuit No. 410 to coolant sensor. When engine is cold, sensor resistance is high, this means ECM will see high signal voltage. When engine warms, sensor resistance lowers and voltage drops. With engine at normal operating temperature, 176-203°F (80-95°C), voltage will measure approximately 1.5-2.0 volts at the ECM.

1. If signal voltage indicates a coolant temperature more than 285°F (140.5°C), this will set a Code 15.
2. This will check if circuit No. 410 is shorted to ground which will cause conditions for a Code 15.