P0125
Diagnostic Chart:
Diagnostic Chart:
Wiring Diagram:
CIRCUIT DESCRIPTION
When the vehicle is first started, the engine operates in an Open Loop operation, ignoring the oxygen sensor signal and calculating the air/fuel ratio based on inputs from the Engine Coolant Temperature (ECT), the throttle position and the manifold absolute pressure sensors only. The PCM will begin by using the oxygen sensor signal for controlling the fuel delivery (Closed Loop) when the following conditions are met:
^ The engine has run a minimum amount of time based on ECT at engine start up.
^ The Oxygen Sensor (O2S 1) has a varying voltage output showing that it is hot enough to operate properly.
^ The ECT has increased a minimum amount based on the ECT at engine start up.
CONDITIONS FOR SETTING THE DTC
Region 1
^ The Intake Air Temperature (IAT) is greater than 10°C (50°F).
^ The ECT is greater than 10°C (50°F).
^ The engine run time is greater than 120 seconds.
^ The maximum idle time is less than 90 seconds.
OR
Region 2
^ The IAT is greater than -7°C (45°F).
^ The ECT is greater than 7°C (45°F).
^ The engine run time is greater than 300 seconds.
^ The maximum idle time is less than 225 seconds.
OR
Region 3
^ The IAT is greater than -7°C (45°F).
^ The ECT is less than -7°C (45°F).
^ The engine run time is greater than 1350 seconds.
^ The maximum idle time is less than 1013 seconds.
The conditions below are present for all three regions.
^ The minimum calculated airflow is less than 10 gps to be considered at idle for all three temperature regions.
^ The ECT is less than 40°C (113°F).
^ The vehicle is in an Open Loop operation.
^ No DTCs P0112, P0113, P0117 or P0118.
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 malfunction present.
^ The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.
^ A history DTC stores.
CONDITIONS FOR CLEARING THE MIL/DTC
^ The MIL will turn off after 3 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.
^ A scan tool can clear the DTCs.
DIAGNOSTIC AIDS
A skewed ECT sensor or a stuck open thermostat will cause DTC P0125 to set.
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.
Check for a poor connection or a damaged PCM harness. Inspect the ECT sensor signal circuit and the ground circuit terminals for the following conditions:
Improper mating.
- Broken locks.
- Improperly formed connectors.
Damaged terminals.
A poor terminal to wire connection.
Damaged harness.
Perform an intermittent test. If the connections and the harness check OK, monitor a digital voltmeter connected between ECT sensor signal circuit and ground circuit terminals while moving the related connectors and the wiring harness.
If a fault is induced, the resistance reading will change. This may help in order to isolate the location of the malfunction.
Use the Temperature vs. Resistance table below in order to evaluate the possibility of a skewed sensor. Refer to Specifications / Electrical / Temperature vs Resistance.
TEST DESCRIPTION
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.
2. The engine must be allowed to cool fully before the ECT and IAT sensors will read close to the ambient temperature in order to check for a possible skewed ECT sensor.
3. Measure the engine coolant temperature with a thermometer to determine the actual value the ECT sensor should be. Take into consideration if the engine has been run and the engine coolant has been warmed without opening the thermostat.
5. This step simulates a DTC P0118. If the PCM senses the change, the PCM and wiring are OK.
6. The ECT sensor, PCM and wiring have checked OK at this point. Check for a proper thermostat and cooling fan operation.
9. Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Tech line information for PCM reprogramming and also refer to the Crankshaft Position (CKP) System Variation Learn Procedure for the Crankshaft Position System Variation Procedure.