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.
Thermostat Monitor
The thermostat monitor is designed to verify correct thermostat operation. The thermostat monitor checks for a thermostat that is operating correctly by estimating engine coolant temperature based on calibrated parameters of engine fueling and ambient temperature. The thermostat monitor compares the actual engine coolant temperature to the expected calibrated engine coolant temperature. If the actual engine coolant temperature is not within the calibrated value of the expected temperature, a DTC sets and the malfunction indicator lamp (MIL) is illuminated. This monitor is executed once per drive cycle.
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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.