Code 15 - Coolant Sensor Circuit Open: Notes
The Coolant Temperature Sensor (CTS) uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on circuit No. 410 to the sensor. When the engine is cold, sensor resistance is high and the ECM sees a high signal voltage. As the engine warms, the sensor resistance becomes less and the voltage drops. At operating temperature, voltage will measure about 1.5-2 volts at ECM terminal "YC16". Coolant temperature is used to control, fuel delivery, Engine Spark Timing (EST), knock control (ESC), Idle Air Control (IAC) and Torque Converter Clutch (TCC).
COOLANT TEMPERATURE SENSOR RESISTANCE VALUES
| Temperature In °F (°C) | Ohms Resistance Should Be: |
|---|---|
| 210 (100) | 185 |
| 160 (70) | 450 |
| 100 (38) | 1800 |
| 70 (20) | 3400 |
| 40 (4) | 7500 |
| 20 (-7) | 13,500 |
| 0 (-18) | 25,000 |
| -40 (-40) | 100,700 |
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Code 15 will set if signal voltage indicates a coolant temperature less than -47°F (-44°C) for 20 seconds.
- This test simulates conditions for a Code 14. If ECM recognizes low signal voltage and scan tool indicates 130°C, ECM and wiring are not at fault.
- This test will determine if circuit No. 410 is open. Five volts should present at sensor connector if measured with digital voltmeter.