DTC P0125: Closed Loop Temp Not Reached: Testing

NOTE: To diagnose this DTC, manufacturer recommends allowing vehicle to sit overnight in order to have a totally cold engine. If any ECT sensor DTCs are present, repair those DTCs before continuing with this test. Extremely cold outside ambient temperatures may have caused this DTC to set.

Ensure coolant level is in good condition and at proper level. Replace or top off coolant as necessary. If coolant is okay, go to next step.
Turn ignition on. Using scan tool, read ENG COOLANT TPM DEG value. If engine was allowed to sit overnight, scan tool temperature value should be near ambient air temperature. If engine coolant temperature is more than 180°F (82°C), allow engine coolant temperature to cool down to 150°F (66°C) before proceeding. If engine coolant temperature is 150°F (65°C) or less, start engine. Using scan tool, monitor ENG COOLANT TPM DEG until engine coolant temperature reaches 180°F (82°C). Temperature value should increase smoothly from start-up to normal operating temperature. Monitor coolant temperature and note when thermostat opens. Thermostat should open at about 195°F (90°C). Replace thermostat as necessary. If thermostat opens as specified, go to next step.
Turn ignition on. Using scan tool, read ENG COOLANT TPM DEG value. If engine was allowed to sit overnight, scan tool temperature value should be near ambient air temperature. If engine coolant temperature is more than 180°F (82°C), allow engine coolant temperature to cool down to 150°F (66°C) before proceeding. If engine coolant temperature is 150°F (65°C) or less, start engine. Using scan tool, monitor ENG COOLANT TPM DEG until engine coolant temperature reaches 180°F (82°C). Temperature value should increase smoothly from start-up to normal operating temperature. Also monitor actual coolant temperature with a thermometer. As engine warms up to normal operating temperature, actual coolant temperature should be relatively close to temperature reading on scan tool. If thermometer reading is relatively close to the scan tool reading, test is complete. If thermometer reading is not relatively close to the scan tool reading, go to next step.
Turn ignition off. Disconnect PCM connectors. PCM is located on left side of engine compartment, near front of battery. Visually inspect connectors for corroded, damaged, pushed-out or miswired terminals. Repair connectors as necessary. If connectors are okay, go to next step.
Disconnect ECT sensor connector. ECT sensor is located in thermostat housing (2.4L) or is threaded into a coolant passage near thermostat housing (3.3L and 3.8L). Visually inspect connector for corroded, damaged, pushed-out or miswired terminals. Repair connector as necessary. If connector is okay, replace ECT sensor.