P0125

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

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 start-up 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 start-up and the amount of air cycled through the engine since start-up.

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 three 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 forty 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 (PCM) Description, Clearing Diagnostic Trouble Codes.

DIAGNOSTIC AIDS

NOTE: Refer to Connector Test Adapter Kit J 35616-A Notice in Service Precautions.

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.
Refer to Engine Falls To Reach Normal Operating Temperature.
^ The cooling fans operation.
Refer to Electrical Cooling Fan Diagnosis. Component Tests and General Diagnostics
^ 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 and Poor Connections in Diagrams.
^ 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 (ECT) 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. Intermittent Conditions

TEST DESCRIPTION
The numbers below refer to step numbers on the diagnostic table.
7. 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 similar to the actual coolant temperature, replace the ECT sensor. If the temperatures are similar, the malfunction is intermittent. Refer to Diagnostic Aids.