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: ECT Sensor 1 Malfunction/Slow Response
- Start the engine, and let it idle for 5 minutes or more.
- Check the ECT SENSOR 1 in the DATA LIST with the HDS.
Is about 10°F (-12°C) or less indicated?
YES -Check for poor connections or loose terminals at ECT sensor 1, ECT sensor 2 and the PCM. If the connections and the terminals are OK, replace ECT sensor 1 (see ECT SENSOR 1 REPLACEMENT ), then Go to step 7.
NO -Go to step 3.
- Turn the ignition switch to LOCK (0).
- Allow the engine to cool to 104°F (40°C) or less.
- Start the engine, and let it idle until ECT sensor 1 goes up to about 158°F (70°C).
Does the ECT sensor 2 also read about 158°F (70°C)?
YES -Go to step 6.
NO -Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at ECT sensor 1, ECT sensor 2, and the PCM.
- Check the thermostat (see
THERMOSTAT TEST
).
Is the thermostat OK?
YES -Check for poor connections or loose terminals at ECT sensor 1, ECT sensor 2 and the PCM, If the connections and the terminals are OK, replace ECT sensor 1 (see ECT SENSOR 1 REPLACEMENT ), then Go to step 7.
NO -Replace the thermostat (see THERMOSTAT REPLACEMENT ), then Go to step 7.
- Turn the ignition switch to LOCK (0).
- Allow the engine to cool 104°F (40°C) or less.
- Start the engine, and let it idle until ECT sensor 1 goes up to about 158°F (70°C).
Does the ECT sensor 2 also read about 158°F (70°C)?
YES -Go to step 1 and recheck.
NO -Troubleshooting is complete.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.