P0125

P0125 Coolant Temp Insufficient For Closed Loop Fuel Control




Circuit Description
When the vehicle is first started, it operates in Open Loop, ignoring the oxygen sensor (O25) signal and calculating the fuel/air ratio based on inputs from the Engine Coolant Temperature (ECT), throttle position (TP) and manifold absolute pressure (MAP) sensors only. The powertrain control module (PCM)/engine control module (ECM) will begin using the O2S signal for controlling fuel delivery (Closed Loop) when the following conditions are met:
- The engine has run a minimum amount of time based on ECT at engine start up.
- The O2S has a varying voltage output showing that it is hot enough to operate properly.
- The ECT has increased a minimum amount based on ECT at engine start up.

Conditions for Setting the DTC
- If ambient temperature is greater than or equal to 50 °F (10 °C) the time for coolant to reach a stabilized closed loop value (70.7 °F [21.5 °C]) is less than or equal to 2 minutes.
- If ambient temperature is between 20 °F (-7 °C) and 50 °F (10 °C) and the time for coolant to reach a stabilized closed loop value (70.7 °F [21.5 °C]) is less than or equal to 5 minutes.
- If ambient temperature is between -35 °F (-37 °C) and 20 °F (-7 °C) the time for coolant to reach a stabilized closed loop value (68 °F [20 °C]) is less than or equal to 15 minutes.
- Engine running.
- DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0201, P0202, P0203, P0204, P0351, P0352, P0502 and P1627 are not set.
- Start-up coolant temperature is 91 °F (33 °C).
- If the ambient temperature is greater than or equal to 50 °F (10 °C) the accumulated airflow is greater than 800 grams and accumulated idle time is less than 90 seconds.
- If ambient temperature is between 20 °F (-7 °C) and 50 °F (10 °C) the accumulated airflow is greater than 820 grams and accumulated idle time is less than 225 seconds.
- If ambient temperature is between -35 °F (-37 °C) and 20 °F (-7 °C) the accumulated airflow is greater than 2700 grams and accumulated idle time is less than 630 seconds.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM/ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history Diagnostic Trouble Code (DTC) is stored.
- Both Cooling fan turns on.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.

Diagnostic Aids
When DTC P0125 is set, a skewed ECT sensor or a stuck-open thermostat is indicated.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside the insulation.

Check for a poor connection or damaged PCM/ECM harness. Inspect the ECT sensor signal circuit and ground circuit terminals for the following conditions:
- Improper mating
- Broken locks
- Improperly formed
- Damaged terminals
- Poor terminal-to-wire connection
- Damaged harness

Perform an intermittent test. If connections and harness check OK, monitor a digital voltmeter connected between ECT sensor signal circuit and ground circuit terminals while moving related connectors and wiring harness. If a fault is induced, the resistance reading will change. This may help to isolate the location of the malfunction.

Use the Temperature vs. Resistance table to evaluate the possibility of a skewed sensor.

Step 1 - 4:

Step 5 - 11:

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
2. The engine must be allowed to cool fully before the ECT and IAT sensors will read close to the ambient temperature in order to check for a possible skewed sensor.
3. Measure the engine coolant temperature with a thermometer to determine the actual value the ECT sensor should be. Take into consideration if the engine has been run and the engine coolant has been warmed without opening the thermostat.
5. This step simulates a DTC P0118. If the PCM/ECM senses the change, the PCM/ECM and wiring are OK.
6. The ECT sensor, PCM/ECM and wiring have checked OK at this point. Check for a proper thermostat and cooling fan operation.
8. The replacement PCM/ECM must be reprogrammed. Refer to the latest Techline procedure for PCM/ECM reprogramming.