Code 15 (1.6L Turbo) - Cts Circuit (Low 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 A11. Coolant temperature is an input used by the ECM to control fuel delivery, Electronic Spark Control (EST) and engine idle speed.

1. This determines if code set because of a hard failure or an intermittent condition. Code 15 sets if signal voltage indicates a coolant temperature less than -38°F (-39°C) after engine has been running for 1 minute.
2. This simulates conditions for Code 14. 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.