P0125

System Description
When the engine coolant temperature is below 20°C (68°F), the fuel delivery system will operate in "Open Loop." The Powertrain Control Module (PCM) ignores the oxygen sensor signal and calculates the air/fuel ratio based on inputs from the engine coolant temperature, throttle position and manifold absolute pressure sensors.

Conditions For Setting The DTC
- The Engine Coolant Temperature (ECT) sensor is less than 60°C (140°F)
- The Intake Air Temperature (IAT) sensor is greater than 20°C (68°C)
- The vehicle speed is greater than 5 mph
- The engine run time is greater than 363 seconds

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 and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The ML will turn "OFF" after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- DTCs can be cleared by using a scan tool.

Engine Coolant Temperature (ECT) Circuit:

Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.
- Check for poor connection or damaged hamess. Inspect PCM harness for backed out terminals and for improper mating, broken locks, and damaged harness.
- Perform an intermittent test. Whenever connections and the harness checks OK, monitor a digital voltmeter connected between the ECT signal circuit and the ECT ground circuit on the PCM harness while moving related connectors and wiring harness. Whenever a fault is induced, the resistance reading will change. This may help to isolate the location of the malfunction.

Engine Coolant Temperature (ECT) Sensor Temperature Vs. Resistance Chart:

- Use the Table to check to check for a skewed sensor.

DTC P0125 - Insufficient Coolant Temperature For "Closed Loop" Fuel Control (1 Of 2):

DTC P0125 - Insufficient Coolant Temperature For "Closed Loop" Fuel Control (2 Of 2):

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The OBD System Check prompts the Technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.
2. Allow the engine to cool to ambient and compare the ECT sensor to the IAT sensor. The AT sensor and ECT sensor should read within 40°C of each other.
This step checks the initial operation of the ECT sensor.
8. Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCM must be reprogrammed.