Refer to Engine Controls Schematics
A/C Pressure Switch, TPS, MAP, ECT and IAT
.
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 PCM controls fuel delivery in open loop, ignoring the heated oxygen sensor (HO2S) 1 signal and calculating the air to fuel ratio based on inputs from the engine coolant temperature (ECT) sensor, the throttle position (TP) sensor, 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 1 signal is varying, indicating that the sensor is hot enough to operate properly. |
| • | The ECT sensor indicates a coolant temperature above 10°C (50°F). |
| • | The time since startup is at least 10 seconds for a warm engine or 50 seconds for a cold engine. |
Conditions for Running the DTC
| • | No intake air temperature (IAT) or ECT sensor DTCs are present. |
| • | The intake air temperature is more than -7°C (+19°F). |
| • | The engine coolant temperature is more than -40°C (-40°F). |
| • | The start up coolant temperature is less than 50°C (122°F). |
Conditions for Setting the DTC
An excessive amount of time passes before the engine coolant temperature reaches the Closed Loop operation threshold of 10°C (50°F). The amount of time ranges between 2 and 13 minutes depending on the engine coolant temperature at startup and the amount of air cycled through the engine since startup.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL OFF after 3 consecutive drive trips during which the diagnostic runs and passes. |
| • | A last test failed, or the current DTC, clears when the diagnostic runs and passes. |
| • | A History DTC clears after 40 consecutive warm-up cycles, if no other emission related diagnostic failures are reported. |
| • | Use a scan tool in order to clear the MIL diagnostic trouble code. |
| • | Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module Description , Clearing Diagnostic Trouble Codes. |
Diagnostic Aids
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
The DTC P0125 diagnostic test will not run if the engine is started while the coolant temperature is less than 0°C (+32°F) or more than 21°C (70°F). If it is not possible to operate the vehicle under the appropriate conditions, check the following items:
| • | The cooling system coolant level. |
| • | The thermostat operation. |
| • | The cooling fans operation. |
| Refer to Electric Cooling Fan Diagnosis . |
| • | Check for high resistance in wiring related to the ECT sensor. Also, check for poor connections at ECT sensor and PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | DTC P0125 may be the result of 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, and the ECT circuit and connections check out OK, replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . |
If DTC P0125 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.
If the problem is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to step numbers on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Important:: The time to Closed Loop can not be tested if start-up coolant temp is 21°C (70°F) or more. If it is not possible to cool the engine below this temperature do not use this table. Refer to Diagnostic Aids.
Does the ECT increase to above the specified value within 2 minutes? | 21°C (70°F) | Go to Diagnostic Aids. | |
3 | Is DTC P0117, P0118, P0480 or P0481 set? | -- | Diagnose these DTCs first | |
4 |
Are the cooling fans off? | -- | ||
5 | Check the cooling system coolant level. . Is the coolant level OK? | -- | ||
6 | Check for correct operation of the thermostat . Refer to Engine Fails To Reach Normal Operating Temperature in Engine Cooling. Is the thermostat operating correctly? | -- | ||
Compare the Engine Coolant Temperature displayed on the scan tool to the actual coolant temperature measured with a thermometer. Is the Engine Coolant Temperature registered by the scan tool within the specified value of the measured temperature? | ± 3°C (± 5°F) | |||
8 |
Was a problem found? | -- | ||
9 | Refer to Engine Fails To Reach Normal Operating Temperature in Engine Cooling for cooling system diagnosis and repair the condition as necessary. Is the action complete? | -- | -- | |
10 | Replace the loose terminals or repair malfunctioning wiring as necessary. Refer to Testing for Intermittent Conditions and Poor Connections or Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
12 |
Does the ECT increase to above the specified value within 2 minutes? | 21°C (70°F) | ||
13 | Review the Captured Info using the scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
