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 Temp Sensor (Cts) CKT, High Temp Indicated: Notes
The Coolant Temperature Sensor (CTS) uses a thermistor to control signal voltage to ECM. ECM applies voltage on Red/Yellow wire to coolant sensor. ECM monitors the voltage across the CTS and converts it into a temperature reading. When engine is cold, sensor resistance is high. ECM will sense high signal voltage. As engine warms, sensor resistance lowers and voltage drops.
Code 15 will set if voltage input at ECM indicates a coolant temperature greater than 284°F (140°C) for at least 5 seconds.
- This test simulates Code 14. If ECM stores Code 14, ECM and wirings are okay, and CTS is faulty. If Code 15 resets, CTS is okay and wiring to ECM or ECM is faulty.
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.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.