P0125

Diagnostic Chart:

Wiring Diagram:

Circuit Description

The engine operates in open loop when first started. In open loop the PCM ignores the oxygen sensor signal and calculates the air/fuel ratio based on inputs from the engine coolant temperature sensor, the throttle position sensor, and the Manifold Absolute Pressure sensor (MAP). The PCM will begin closed loop fuel control when the oxygen sensor signal is active enough and the Engine Coolant Temperature (ECT) sensor reaches a predetermined coolant temperature. The PCM expects to begin closed loop fuel control within a specified amount of time.

Conditions for Running the DTC

^ The HO2S 1 output is varying, indicating that the sensor is hot enough to operate properly.

^ Fuel level greater than 25%.

^ Intake air temperature is between -10°C (14°F) and 50°C (122°F).

^ Barometric pressure greater than 75 kPa.

Conditions for Setting the DTC

^ Engine coolant temperature sufficient to allow Closed Loop operation is not achieved within a predetermined time frame.

^ Diagnostic will run once per drive cycle.

Action Taken When the DTC Sets

^ The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC

^ The MIL will turn OFF after three consecutively passing cycles without a fault present.

^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.

^ DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed.

Diagnostic Aids

A DTC P0125 could indicate 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. Replace the ECT sensor if the displayed engine coolant temperature is not close to the actual engine coolant temperature.

Check for any of the following conditions:

^ A poor connection at the PCM. Inspect the harness connectors for backed out terminal, improper mating, broken locks, improperly formed or damaged terminals, and a poor terminal to wire connection.

^ A damaged wiring harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving connectors and wiring harnesses related to the ECT sensor. A change in the ECT display will indicate the location of the fault.

^ Check for the proper operation of the thermostat.

If a DTC P0125 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

If any wiring repairs need to be made, Refer to Repair Procedures in Electrical Diagrams.

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. Compares the ECT temperature to the Intake Air Temperature (IAT) temperature. The ECT sensor and IAT sensor temperature readings should be close [within 3°C (5°F)] to each other especially if the vehicle has been sitting overnight.

3. The ECT sensor may not take as long as ten minutes to reach 40°C (104°F). This is an average time and depends on the ambient temperature.

5. Measure the actual ambient air temperature and compares that to the ECT display on the scan tool.