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.
Theory Of Operation
The Powertrain Control Module (PCM) compares Engine Coolant Temperature (ECT), Intake Air Temperature (IAT), and Ambient Air Temperature (AAT) under cold start conditions. Following a start to run delay time, the sensor values are compared. If the one sensor value is not within a specified range of the other two sensors, the value is determined to be irrational. Once the general temperature rationality is passed, the PCM determines that the general temperature sensor values are correct. The PCM compares the Engine Oil Temperature Sensor value to a threshold based on the other temp sensor values. If the difference is greater than a calibrated value, the diagnostic fails.
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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.