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 Sensor Open
Code 15 means the ECM has seen the resistance of the Coolant Sensor circuit too high. This could be due to high resistance (cold engine temperature) or high voltage at ECM term. "3", for too long a time. This may cause detonation on a warm engine due to excessive spark advance, or poor driveability due to inaccurate fuel control.
- If problem still exists, "CHECK ENGINE" light will come on and Code 15 will be set.
- This test checks if fault is coolant sensor or lack of voltage to sensor. Normal reading is 5 volts across coolant sensor connector.
- This test determines whether the low voltage at the sensor connector is due to opens in the coolant sensor wires, or in another part of the 5 volt reference circuit. Normal voltage is about 5 volts from ECM terms. "3" to "7."
- This test checks resistance of the coolant sensor. If the resistance is within the chart specifications, coolant sensor is not faulty. Check for corrosion at the connector or low coolant level.
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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.