DTC P0125: ECT Sensor 1 Malfunction/Slow Response

1. Start the engine, and let it idle for 5 minutes or more.
2. Check ECT SENSOR 1 in the DATA LIST with the HDS.

   Is about 0°F (-18 °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 MAF SENSOR/IAT SENSOR REPLACEMENT ).

   NO  -Go to step 3.

3. Turn the ignition switch to LOCK (0).
4. Allow the engine to cool to 104 °F (40 °C) or less.
5. Make sure the temperature difference between ECT SENSOR 1 and ECT SENSOR 2 is about 50 °F (10 °C) in the DATE LIST with the HDS.
6. Start the engine, and let it idle until ECT sensor 1 reads about 158 °F (70 °C).

   Does ECT sensor 2 also read about 158 °F (70 °C)? 

   YES  -Go to step 7.

   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.

7. Check the thermostat (see FAN MOTOR 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 MAF SENSOR/IAT SENSOR REPLACEMENT ), then go to step 8.

   NO  -Replace the thermostat (see THERMOSTAT REPLACEMENT ), then go to step 8.

8. Turn the ignition switch to ON (II).
9. Reset the PCM with the HDS.
10. Turn the ignition switch to LOCK (0).
11. Allow the engine to cool to 104 °F (40 °C) or less.
12. Make sure the temperature difference between ECT SENSOR 1 and ECT SENSOR 2 is about 50 °F (10 °C) in the DATE LIST with the HDS.
13. Start the engine, and let it idle until ECT sensor 1 reads about 158 °F (70 °C).

Does ECT sensor 2 also read about 158 °F (70 °C)? 

YES  -Go to step  1 and recheck.

NO  -Troubleshooting is complete.