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 Low Temperature Indicated: Notes
The coolant temperature sensor uses a thermistor to control signal voltage to the ECM. The ECM applies voltage on the Gray/White wire to the sensor. When engine is cold, thermistor resistance is high. This means the ECM will see high signal voltage.
As engine warms, thermistor resistance is less. This means the ECM will see low signal voltage. When engine reaches normal operating temperature approximately 176-203°F (80-95°C), signal voltage will be approximately 1.5-2.0 volts at the ECM. Coolant temperature is one of the inputs the ECM uses in determining fuel delivery and ignition timing.
- Code 15 will set if signal voltage indicates coolant temperature is more than 276°F (135°C) for 3 seconds.
- This checks Gray/White wire for a short to ground causing the conditions for a Code 15.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.