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

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 sees 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 measures 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 sets a Code 15.
2. This checks if circuit No. 410 is shorted to ground, which causes conditions for a Code 15.