P0125

DTC P0125 Engine Coolant Temperature Excessive Time To Closed Loop Fuel Control:

Heated Oxygen Sensor (HO2S) Circuit:

CIRCUIT DESCRIPTION

When the vehicle is first started, it operates in "Open Loop," ignoring the oxygen sensor signal and calculating the air/fuel ratio based on inputs from the engine coolant temperature, throttle position, and mass air flow sensors. The ECM will begin using the oxygen sensor signal for controlling fuel delivery ("Closed Loop") when the following conditions are met:


CONDITIONS FOR RUNNING THE DTC

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


CONDITIONS FOR SETTING THE DTC

- Engine coolant temperature sufficient to allow "Closed Loop" operation (20°C/68°F) 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 ECM 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.

- DTC(s) can be cleared by using a scan tool or by disconnecting the ECM battery feed.

DIAGNOSTIC AIDS


DTC P0125 set indicates a "skewed" Engine Coolant Temperature (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, replace the ECT sensor.

Check the following conditions:

- Poor connection at ECM. Inspect harness connectors for backed out terminal, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

- Damaged 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 proper operation of the thermostat.

If 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 Diagrams.


TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Engine 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 ECT temperature to the Intake Air Temperature (IAT) temperature.

6. Measure actual ambient air temperature as compares that to the ECT display on the scan tool.