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P0125

DTC P0125 Engine Coolant Temperature (ECT) Excessive Time to Closed Loop Fuel Control




Circuit Description
When the vehicle is first started, the engine operates in an open loop operation. During open loop operation, the PCM ignores the oxygen sensor signal when calculating the correct air/fuel ratio. Instead, fuel delivery is controlled using inputs from the engine coolant temperature (ECT) sensor, the throttle position (TP) sensor and the manifold absolute pressure (MAP) sensor. Closed loop operation, during which the PCM uses the oxygen sensor signal to control fuel delivery, begins 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 Running the DTC
- Region 1 - Ambient Temperature Above 10° C (50° F)
- The intake air temperature (IAT) is more than 10° C (50°F).
- The ECT is more than 10° C (50° F).
- The engine has been running for more than 120 seconds.
- The maximum idle time is less than 90 seconds.

OR

- Region 2 - Ambient Temperature Above -7° C (19° F)
- The IAT is more than -7° C (19° F).
- The ECT is more than -7° C (19° F).
- The engine has been running for more than 300 seconds.
- The maximum idle time is less than 225 seconds.

OR

- Region 3 -Ambient Temperature Below -7° C (19° F)
- The IAT is less than -7° C (19° F).
- The ECT is less than -7° C (19° F).
- The engine has been running for more than 1350 seconds
- The maximum idle time is less than 1013 seconds

The conditions below are present for all three regions.
- There are no active MAP DTCs
- There are no active ECT DTCs
- There are no active IAT DTCs
- There are no active TP DTCs
- There are no active fuel trim DTCs
- There are no active injector control DTCs
- There are no active misfire DTCs
- There are no active crankshaft position (CKP) DTCs
- There are no active camshaft position (CMP) DTCs
- There are no active evaporative emissions (EVAP) DTCs
- There are no active idle air control (IAC) DTCs
- There are no active PCM memory DTCs
- The minimum calculated airflow is less than 10 gps to be considered at idle for all three temperature regions.

Conditions for Setting the DTC
The conditions below are present for all three regions.
- The ECT is less than 40° C (104° F).
- The vehicle is in open loop operation.

Action Taken When the DTC Sets
- The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive ignition cycles.
- The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is recorded in the scan tool's Freeze Frame and Failure Records.

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.
- The DTCs can be cleared using the scan tool Clear Information function.

Diagnostic Aids
An incorrectly calibrated ECT sensor or a thermostat that is stuck open will cause DTC P0125 to set.

Use the Temperature vs. Resistance table below in order to evaluate the possibility of a skewed sensor. Refer to Temperature vs Resistance.

Check for a faulty 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
- Poor terminal to wire connections
- A damaged harness

If the connections and the harness are OK, perform an intermittent test.: Monitor a digital voltmeter connected between the ECT sensor signal circuit and the 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 isolate the location of the malfunction.

An intermittent may be caused by any of the following conditions:
- A poor connection
- Rubbed through wire insulation
- A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs.

Steps 1 - 4:




Steps 5 - 8:




Steps 9 - 11:




Steps 12 - 16:




Step 17:




Test Description
The numbers below refers to the step numbers on the Diagnostic Table.
1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
2. Allow the engine to fully cool. The ECT sensor and the IAT sensor 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 in order to determine what the actual value the ECT sensor should be. Take into consideration if the engine has been operating and if the engine coolant has been warmed.
5. This step simulates a DTC P0118. The PCM and wiring are OK if the PCM senses a change.
14. Program the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Isuzu Technical Communication System (ITCS) information for PCM programming.


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