Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
- If signal voltage indicates a coolant temperature more than 285°F (140.5°C), this sets a Code 15.
- This checks if circuit No. 410 is shorted to ground, which causes conditions for a Code 15.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.