P0125

CIRCUIT DESCRIPTION

Schematic:

The PCM uses a closed loop air/fuel metering system to provide the best possible combination of driveability, fuel economy, and emission control. When the vehicle is first started, the PCM controls fuel delivery in an open loop mode. The PCM ignores signal from the fuel control heated oxygen sensors (HO2S bank 1 sensor 1 and HO2S bank 2 sensor 1). The PCM calculates the air/fuel ratio from the engine coolant temperature, throttle position, and mass air flow sensors. The PCM uses the fuel control sensors to control fuel delivery (Closed Loop) when the following conditions are met:
^ The PCM monitors the HO2S bank 1 sensor 1 and HO2S bank 2 sensor 1 voltage signals switching from below 300 mV to above 600 mV.
^ The engine coolant temperature sensor indicates an engine coolant temperature above 84°C (183°F).
^ Time since start-up is at least 10 seconds for a warm engine or 2 minutes for a cold engine.

CONDITIONS FOR RUNNING THE DTC
^ No ECT, IAT, MAF or VSS DTCs are set.
^ Engine running.
^ Start-up ECT is less than 40°C (104°F).
^ Engine coolant temperature is more than -40°C (-40°F).
^ Intake air temperature is more than 40°C (-40°F) but less than 40.2 °C (104°F).
^ Vehicle speed is more than 1.6 km/h (1 MPH).

CONDITIONS FOR SETTING THE DTC
The length of time for the engine coolant to reach a stabilized temperature of 68°C (154°F) takes longer than it should. The amount of time ranges between 2 and 23 minutes depending on engine coolant temperature at start-up and the amount of air cycled by the engine since start-up

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test runs and fails.
^ The PCM stores the conditions present when the DTC set as Freeze Frame and Fail Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the MIL OFF after the third consecutive trip in which the diagnostic runs and passes.
^ 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 Clear DTC Information function.

DIAGNOSTIC AIDS

NOTE: Refer to Connector Test Adapter Kit J 35616-A Notice in Service Precautions.

^ The cooling system coolant level. Refer to Loss of Coolant in Engine Cooling.
^ The thermostat operation. Refer to Thermostat Diagnosis in Engine Cooling. Cooling System
^ The cooling fan operation. Refer to Electric Cooling Fan Diagnosis. Component Tests and General Diagnostics
^ Check for high resistance in the wiring related to the ECT sensor. Also, check for poor connections at the ECT sensor and PCM. Refer to Wiring Repairs in Diagrams.
^ DTC P0125 may set due to a skewed ECT sensor. To help isolate this condition, compare the engine coolant temperature display on the scan tool with the actual coolant temperature measured with a thermometer. If the displayed engine coolant temperature value is not close to the actual coolant temperature, replace the ECT sensor.

If the conditions is intermittent, refer to Intermittent Conditions in Symptoms. Intermittent Conditions

TEST DESCRIPTION

Steps 1 - 12:

The number below refers to the number in the diagnostic table.
6. 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.

If the temperatures are close, the malfunction is intermittent. Refer to Diagnostic Aids.