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

Coolant temperature sensor controls signal voltage to ECM, which applies voltage on circuit No. C10 to 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 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 volt-ohmmeter.