Circuit Description
In order to provide the best possible combination of driveability, fuel economy, and emissions control, a closed loop air-to-fuel metering system is used. When the vehicle is first started, the powertrain control module (PCM) controls the fuel delivery in open loop, ignoring the heated oxygen sensor (HO2S) signals and calculating air-to-fuel ratio based on inputs from the engine coolant temperature (ECT), the throttle position (TP), and the mass air flow (MAF) sensors. The PCM will begin using the HO2S 1 signal for controlling fuel delivery, closed loop. when the following conditions have been met:
| • | The HO2S output signal is varying, indicating that the sensor is hot enough to operate properly. |
| • | The ECT sensor indicates that the coolant temperature is more than 15°C (64°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 amount of time that is needed for the cooling system to achieve closed loop operating temperature. This diagnostic is broken into three temperature regions. The diagnostic uses the engine coolant temperature (ECT) and intake air temperature (IAT) sensors in order to determine the region in which to operate. The time needed in order to achieve the 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 diagnostic trouble code (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 50°C (122°F). |
| • | The Region 1 air temperature is more than 10°C (50°F) and the startup coolant temperature more than 10°C (50°F) . |
| • | The Region 2 air temperature is more than -7°C (20°F) and the startup coolant temperature is between -7°C (20°F) and 10°C (50°F). |
| • | The Region 3 air temperature is more than -7°C (20°F) and the startup coolant temperature is between -40°C (-40°F) and -7°C (20°F). |
Conditions for Setting the DTC
Region 1:
| • | The engine run time takes more than 127 seconds to achieve a closed loop temperature of 15°C (64°F). |
| • | The calibrated minimum amount of total airflow has been exceeded. |
| • | The maximum idle time is less than 95 seconds. |
Region 2:
| • | The engine run time is takes than 280 seconds to achieve a closed loop temperature of 15°C (64°F). |
| • | The calibrated minimum amount of total airflow has been exceeded. |
| • | The maximum idle time is less than 210 seconds. |
Region 3:
| • | The engine run time takes more than 439 seconds to achieve a closed loop temperature of 15°C (64°F). |
| • | The calibrated minimum amount of total airflow has been exceeded. |
| • | The maximum idle time is less than 329 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 with the 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. Refer to Engine Coolant Temperature Sensor Replacement .
Inspect for:
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 numbers below refer to the step numbers 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. Refer to DTC P0336 Crankshaft Position (CKP) Sensor Circuit . | |
3 |
Is the ECT parameter near the specified value? | 140°C (283°F) | ||
4 |
Did you find and correct the condition? | -- | ||
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: The new PCM must be reprogrammed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
8 |
Does the ECT increase to more than the specified value within 9 minutes? | -10°C (14°F) | System OK |
