Code 15 - Cts Circuit (Low Temperature Indicated): Notes

Coolant temperature sensor controls signal voltage to the ECM. The ECM applies voltage on circuit No. C10 to the sensor. When engine is cold, thermistor 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.

1. Code 15 will set if engine is running longer than 30 seconds and coolant temperature is less than -27°F (-33°C) for 3 seconds.
2. This simulates a Code 14. If ECM recognizes low signal voltage, (high temperature) and scan tester reads greater than 266°F (130°C), ECM and wiring are okay.
3. This determines if circuit No. C10 is open. There should be 5 volts present at sensor connector as measured with a high-impedance (10-megohm) digital voltmeter.