GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The DTC P0125 Excessive Time To Closed Loop Fuel Control diagnostic monitors the relationship between running time and engine coolant temperature (ECT) sensor activity. In normal operation, the typical increase in engine temperature will allow the HO2S 1 to become active and go into Closed Loop operation soon after the engine is started.

The powertrain control module (PCM) applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts the voltage into a temperature reading. The PCM will receive a high voltage input when the coolant temperature is cold, and a low voltage input when the coolant temperature is warm. If the PCM fails to detect the expected change in voltage from the ECT sensor after the engine has been running a specified number of seconds, DTC P0125 can set.

Conditions for Running the DTC

    • DTC P0100, P0101, P0102, P0103, P0115, P0117, P0118 are not set.
    • The engine coolant temperature is at a specified value at engine start up.
    • The engine has been running for at least 120 seconds.
    • DTC P0125 runs continuously once the above conditions are met.

Conditions for Setting the DTC

    • Condition 1
        The ECT is less than -7°C (+20°F) at engine start up, and the ECT is 20°C (68°F) or less after running for 20 minutes.
    • Condition 2
        The ECT is between -7 and +10°C (+20 and +50°F) at engine start up, and the ECT is 20°C (68°F) or less after running for 5 minutes.
    • Condition 3
        The ECT is more than 10°C (50°F) at engine start up, and the ECT is less than 20°C (68°F) after running for 2 minutes.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL) during the second key cycle in which the DTC sets.
    • The PCM stores the conditions which were present when the DTC set as Freeze Frame data.

Conditions for Clearing the MIL/DTC

    • The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
    • The DTC clears after 40 consecutive warm-up cycles have occurred without a fault.
    • A DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

Check for any of the following conditions:

    • Check for the proper operation of the engines cooling system, including the correct coolant level. Refer to Engine Fails To Reach Normal Operating Temperature .
    • A faulty thermostat that stays open slightly can cause DTC P0125 to set in cold weather when the vehicle is started and let sit while warming up. Replace any suspect thermostat.
    • Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted ECT sensor. A shifted sensor could result in DTC P0125. Refer to Temperature Versus Resistance .
    • Check for a faulty electrical connection to the PCM.

An intermittent malfunction may be caused by a fault in the ECT sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. The Diagnostic System Check-Engine Controls 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. This step checks for other DTCs that must be diagnosed first.

  3. This step checks for a faulty ECT sensor or ECT sensor circuit.

  4. This step checks the integrity of the ECT sensor input circuit.

  5. This step checks the integrity of the ECT sensor ground circuit.

  6. This step checks the integrity of the ECT sensor input circuit.

  7. A cooling system that prevents the engine from warming up properly and reaching the correct engine operating temperature within a set run time can cause a DTC P0125 to set. A thermostat that stays open slightly can cause a DTC P0125 to set in cold weather when the vehicle is started and let sit while warming up. Replace the thermostat if suspect .

  8. This step determines if DTC P0125 is the result of a hard failure or an intermittent condition.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Are there any DTCs set other than DTC P0116 or P0125?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

  1. Measure the actual coolant temperature.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the ECT sensor parameter on the scan tool.

Is the ECT sensor value displayed near the actual coolant temperature?

--

Go to Step 10

Go to Step 4

4

  1. Disconnect the ECT sensor electrical connector.
  2. Observe the ECT sensor parameter on the scan tool.

Does the engine coolant temperature equal the specified value?

-40°C (-40°F)

Go to Step 5

Go to Step 8

5

  1. Disconnect the ECT sensor electrical connector.
  2. Jump the ECT sensor input circuit and the ground circuit together at the ECT sensor harness connector.
  3. Observe the ECT sensor parameter on the scan tool.

Does the engine coolant temperature equal the specified value?

140°C (284°F)

Go to Step 12

to Step 6

6

  1. Jump the ECT sensor input circuit to chassis ground.
  2. Observe the ECT sensor parameter on the scan tool.

Does the engine coolant temperature equal the specified value?

140°C (284°F)

Go to Step 7

Go to Step 8

7

Repair the open or high resistance in the ECT sensor ground circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 13

Go to Step 9

8

  1. Turn OFF the ignition.
  2. Disconnect the PCM electrical connector C3.
  3. Test the ECT sensor input circuit for a short or a high electrical resistance. Refer to Circuit Testing in Wiring Systems.
  4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 13

Go to Step 9

9

Repair the faulty connection at the PCM or the ECT electrical connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 13

--

10

  1. Inspect the engine cooling system for any of the following conditions:
  2. • A faulty thermostat--Refer to Thermostat Diagnosis
    • A low coolant level--Refer to Cooling System Draining and Filling
    • Incorrect coolant
    • Faulty cooling system operation--Refer to Engine Fails To Reach Normal Operating Temperature
  3. Repair as necessary.

Was a repair necessary?

--

Go to Step 13

Go to Step 11

11

  1. Perform the scan tool Clear DTC Information function.
  2. Place the vehicle into Check Mode, using the scan tool. Refer to Service Bay Test .
  3. Operate the vehicle within the Freeze Frame conditions as specified.

Does DTC P0125 set?

--

Go to Step 12

Go to Diagnostic Aids

12

Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .

Is the action complete?

--

Go to Step 13

--

13

  1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
  2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on scan tool?

--

Go to Step 14

Go to Step 2

14

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK