Circuit Description
In order to provide the best possible combination of driveability, fuel economy, and emission control, a closed loop air-to-fuel l metering system is used. When you start the vehicle, the PCM controls the fuel delivery in open loop, ignores the heated oxygen sensor (HO2S) 1 signal. The PCM then calculates the air-to-fuel ratio based on inputs from the engine coolant temperature, the throttle position, and the mass air flow sensors. The PCM will begin using the HO2S 1 signal, in order to control the fuel delivery in closed loop when the following conditions are met:
| • | The HO2S 1 signal varies, indicating that the sensor is hot enough to operate properly. |
| • | The engine coolant temperature sensor indicates that the coolant temperature is above 20°C (68°F). |
| • | The time since start-up is at least 15 seconds for a warm engine or 90 seconds for a cold engine. |
The PCM monitors the time that is required for the cooling system to achieve closed loop operating temperature. This diagnostic is broken into 3 temperature regions. The diagnostic uses the ECT and IAT sensors in order to determine the region in which to operate. The diagnostic monitors the time that is needed to achieve closed loop temperature, and makes a time-based decision, depending on the temperature region. The diagnostic will monitor the following conditions, which must occur prior to setting the DTC:
| • | The total airflow must exceed a calibrated amount. |
| • | The engine idle time must be less than a calibrated amount. |
Conditions for Running the DTC
| • | There are no active IAT or ECT sensor DTCs present. |
| • | The minimum air temperature is more than -7°C (+19°F). |
| • | The start-up engine coolant temperature is less than 40°C (104°F). |
| • | Region 1 -- The air temperature is more than 10°C (50°F) and the start-up coolant temperature is more than 10°C (50°F). |
| • | Region 2 -- The air temperature is more than -7°C (+19°F) and the start-up coolant temperature is between -7°C (19°F) and 10°C (50°F). |
| • | Region 3 -- The air temperature is more than -7°C (+20°F) and the start-up engine coolant temperature is between -40°C (-40°F) and -7°C (+20°F). |
Conditions for Setting the DTC
Region 1:
| • | The engine run time is more than 6 seconds in order to achieve closed loop temperature of 10°C (50°F). |
| • | A calibrated minimum amount of total air flow has been exceeded. |
| • | The maximum idle time is less than 5 seconds. |
Region 2:
| • | The engine run time is more than 154 seconds, in order to achieve a closed loop temperature of 10°C (50°F). |
| • | A calibrated minimum amount of total air flow has been exceeded. |
| • | A maximum idle time is less than 120 seconds. |
Region 3
| • | The engine run time is more than 287 seconds, in order to achieve a closed loop temperature of -10°C (14°F). |
| • | The calibrated minimum amount of total airflow has been exceeded. |
| • | A maximum idle time is less than 225 seconds. |
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/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has 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 a scan tool. |
Diagnostic Aids
DTC P0125 set indicates a skewed ECT sensor. Comparing the engine coolant temperature displayed on a scan tool to the actual coolant temperature, measured with a thermometer, may help to 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.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
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.
Test Description
The number below refers to the step number on the diagnostic table:
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic System Check? | -- | ||
2 | Are any ECT sensor DTCs set? | -- | Go to applicable DTC. Go to Diagnostic Trouble Code (DTC) List/Type | |
3 |
Is the ECT parameter near the specified value? | 140°C or 284°F | ||
4 |
Did you find a problem? | -- | ||
5 | Replace the faulty terminals, or repair the faulty wiring as necessary. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
6 | Replace ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | -- | |
|
Important: You must program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
8 |
Does DTC P0125 run and pass? | -- | System OK |
