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 powertrain control module (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 PCM monitors the amount of time for the cooling system to achieve Closed Loop operating temperature. This diagnostic is broken into three temperature regions. The diagnostic uses the ECT and IAT sensors to determine which region to operate in. The time to achieve Closed Loop temperature is monitored. A time based decision is made depending on the temperature region. The diagnostic will monitor the following conditions prior to setting the DTC:

1. Total airflow must exceed a calibrated amount.
2. Engine idle time must be less than a calibrated amount.

Region 1:

1. Engine run time is over 6 seconds to achieve Closed Loop temperature of 10°C (50°F).
2. Calibrated minimum amount of total air flow has been exceeded.
3. Maximum idle time is less than 5 seconds.

Region 2:

1. Engine run time is over 154 seconds to achieve Closed Loop temperature of 10°C (50°F).
2. Calibrated minimum amount of total air flow has been exceeded.
3. Maximum idle time is less than 120 seconds.

Region 3

DTC P0125 set indicates a skewed 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 within 10°C (14°F) of the actual coolant temperature, replace the ECT sensor.

Inspect for the following conditions:

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: :  Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

The numbers below refer to the step numbers on the diagnostic table.

7. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.