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.
Engine Coolant Temperature Sensor
The Engine Coolant Temperature (ECT) sensor is a variable resistor that measures temperature of engine coolant. ECT sensor is located on top front of cylinder head, near oil filler tube. See Fig 1 . The ECM supplies 5 volts to the signal circuit. When coolant temperatures are low, resistance is high. When coolant temperatures are high, resistance is low. ECM uses this input for engine controls and enabling criteria for diagnostics. ECM will record the amount of time the engine is off. At restart, ECM will compare the temperature difference between the ECT and Intake Air Temperature (IAT). If temperature difference is not within the calculated amount after the predetermined soak time, a DTC will set. To diagnose, see SELF-DIAGNOSTICS - 6.6L SIERRA & SILVERADO - DIESEL article.
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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.