DTC P0125 Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control. Chevrolet Monte Carlo 1996

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 Monte Carlo 🢒 DTC 🢒 DTC P0125 Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control

Engine Controls Components
ECT, MAP, TP, IAT, and A/C Systems
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

To provide the best possible combination of driveability, fuel economy, and emission control, a closed loop air/fuel metering system is used. When the vehicle is first started, the PCM controls fuel delivery in open loop, ignoring the heated oxygen sensor (HO2S) 1 signal and calculating air/fuel ratio based on inputs from the engine coolant temperature, throttle position, and mass air flow sensors. The PCM will begin using the HO2S 1 signal for controlling fuel delivery (Closed Loop) when the following conditions have been met:

•	The HO2S 1 signal is varying, indicating that the sensor is hot enough to operate properly.

•	The engine coolant temperature sensor indicates coolant temperature above 20°C (68°F).

•	Time since startup is at least 16 seconds for a warm engine or 50 seconds for a cold engine.

Conditions for Setting the DTC

•	No active IAT or ECT DTC(s) present.

•	Startup intake air temperature is greater than 10°C (50°F).

•	Startup engine coolant temperature is between 10°C (50°F) and 26.5°C (80°F).

•	Engine coolant temperature sufficient to allow Closed Loop operation (27.5°C /81.5°F) is not achieved within 3 minutes of startup.

Action Taken When the DTC Sets

•	The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

•	The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC

•	The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.

•	The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

•	The DTC can be cleared by using the scan tool.

Diagnostic Aids

DTC P0125 set indicates a slewed ECT sensor. Comparing the engine coolant temperature displayed on a scan tool with actual coolant temperature measured with a thermometer may isolate this condition. If the displayed engine coolant temperature is not close to the actual coolant temperature, replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .

Check for the following conditions:

•	Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

•	Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.

If DTC P0125 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.