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.
Scan Tool Data Definitions
ECT: The scan tool displays -40°C to +151°C (-40°F to +304°F). The engine coolant temperature (ECT) sensor is mounted in the coolant stream. The Powertrain Control Module (PCM) applies 5 volts to the ECT sensor signal circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold and the internal resistance is high, the PCM monitors a high signal voltage and interprets it as a cold engine. As the sensor warms and the internal resistance decreases, the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.
FC Relay 1 Command: The fan control (FC) relay is commanded by the PCM. FC Relay 1 displays the command as ON or OFF.
High Coolant Temp Lamp: The scan tool displays ON or OFF. The state of the CHECK GAGES indicator as commanded by the instrument panel cluster (IPC). The IPC receives a class 2 message from the Body Control Module (BCM) indicating the coolant temperature.
Low Coolant Lamp: The scan tool displays ON or OFF. The state of the Low Coolant indicator as commanded by the IPC. The IPC receives a class 2 message from the BCM indicating the 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.