The engine operates in open loop when first started. In open loop, the powertrain control module (PCM) ignores the oxygen sensor signal and calculates the air/fuel ratio based on inputs from the engine coolant temperature sensor, the throttle position sensor, and the mass air flow sensor. The PCM will begin closed loop fuel control when the oxygen sensor signal is active enough and the ECT sensor reaches a predetermined coolant temperature. The PCM expects to begin closed loop fuel control within a specified amount of time.

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

Check for any of the following conditions:

If the DTC P0125 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0125 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0125 appears in the Not Ran Since Code Cleared list, the P0125 diagnostic has not yet run. When the DTC P0125 does not appear in the Not Ran Since Code Cleared list, the P0125 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0125 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

An intermittent malfunction may be caused by a fault in the ECT sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:

If you cannot duplicate the DTC P0125, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

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

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and to store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step compares the ECT temperature to the IAT temperature. This inspection is to be performed when the vehicle has reached ambient room temperature. At that time both the surrounding air temperature and the engine coolant temperature are nearly equal. If the ECT sensor and circuit are OK, both sensors should indicate the same temperature.

6. Fault not present indicates the condition that caused a DTC P0125 to set is intermittent and not currently present. If no other DTCs are stored, refer to Diagnostic Aids for additional information on diagnosing an intermittent P0125.

11. After performing the scan tool Clear DTC Information function, the DTC P0125 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0125 appears in the Not Ran Since Code Cleared list, the P0125 diagnostic has not yet run. When the DTC P0125 does not appear in the Not Ran Since Code Cleared list, the P0125 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0125 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.