DTC Troubleshooting

DTC Troubleshooting: P0125

DTC P0125: ECT Sensor 1 Malfunction/Slow Response

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information. Initial Inspection and Diagnostic Overview

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 connection or loose terminals at ECT SENSOR 1, ECT SENSOR 2, and the ECM/PCM. If they are OK, replace ECT SENSOR 1. ECT Sensor 1 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 difference between ECT SENSOR 1 and ECT SENSOR 2 is less than about 50 °F (10 °C) in the DATA LIST with the HDS.

6. 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 show 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 ECM/PCM.


7. Check the thermostat. Testing and Inspection

Is the thermostat OK?
YES - Check for poor connection or loose terminals at ECT sensor 1, ECT sensor 2, and the ECM/PCM. If the connections and the terminals are OK, replace ECT SENSOR 1, ECT Sensor 1 Replacement then go to step 8.

NO - Replace the thermostat, Thermostat Replacement then go to step 8.


8. Turn the ignition switch to ON (II).

9. Reset the ECM/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. Check that the temperature difference between ECT SENSOR 1 and ECT SENSOR 2 is about 50 °F (10 °C) in the DATA LIST with the HDS.

13. 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.