P0125

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 powertrain control module (PCM) controls fuel delivery in "open loop,,, ignoring the heated oxygen sensor (HO2S) signals 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 Bank 1 HO2S 1 and Bank 2 HO2S 1 signals for controlling fuel delivery under "closed loop" conditions when the following conditions have been met:
- The HO2S output signals are varying, indicating that the sensors are hot enough to operate properly.
- The engine coolant temperature sensor indicates coolant temperature above 50°C (122°F).
- Time since start-up is at least 16 seconds for a warm engine or 23 seconds for a cold engine.

Conditions for Setting the DTC
- No active IAT or ECT DTC(s) are present.
- Engine is running.
- Vehicle speed is greater than 5 mph (8 km/h).
- Intake air temperature is greater than -10°C (14°F) 0°C (32°F).
- Start-up engine coolant temperature is between -10°C(-14°F) and 28°C(82°F).
- For a warm engine (intake air temperature is greater than 10°C/50°F), engine coolant temperature sufficient to allow "closed loop" operation (50°C/122°F) is not achieved within 2 minutes of start-up. For a cold engine (intake air temperature between (-7°C and 10°C), engine coolant temperature sufficient to allow "closed loop" operation (50°C/122°F) is not achieved within 10 minutes of start-up.
- The above condition fails 20 consecutive times.

Diagnostic Aids
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 close to the actual coolant temperature, replace the ECT sensor.
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. It 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 Failure Records data can be useful in determining vehicle mileage wince the DTC was last set.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
2. 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 fault is intermittent; refer to Diagnostic Aids.




Specifications








Diagnostic Chart