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.
DTC P0125: Engine Coolant Temperature (ECT) Sensor 1 Malfunction/Slow Response: General Description
The engine control module (ECM)/powertrain control module (PCM) supplies voltage to the engine coolant temperature signal circuit (about 5 V) through a pull-up resistor. As the engine coolant cools, the engine coolant temperature (ECT) sensor 1 resistance increases, and the ECM/PCM detects a high signal voltage. As the engine coolant warms, the ECT sensor 1 resistance decreases, and the ECM/PCM detects a low signal voltage. If the ECT sensor 1 output voltage does not reach a specified temperature at which closed loop control for stoichiometric air/fuel ratio starts within a set time, depending on the initial engine coolant temperature after starting the engine, the ECM/PCM detects a malfunction and stores a DTC.
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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.