For 1990-2009 cars

### Circuit Description

The DTC P0125 Excessive Time To Closed Loop Fuel Control diagnostic monitors the relationship between running time and heated oxygen sensor (HO2S) activity. The HO2S produces a voltage that varies between 0.1-0.9 volts under normal operating conditions. The powertrain control module (PCM) monitors this voltage and determines if the exhaust is lean or rich. If the voltage input at the PCM is about 0.1 volt the exhaust is lean, and if the voltage input is about 0.9 volt the exhaust is rich. The PCM constantly monitors the HO2S 1 signal during Closed Loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary.

In normal operation the HO2S 1 will become active and go into Closed Loop soon after the engine is running. If the PCM fails to receive a high voltage signal from the HO2S 1 after the engine cooling system has reached operating temperatures, DTC P0125 can set.

### Conditions for Running the DTC

• | The engine coolant temperature (ECT) is at least 40°C (140°F).

• | The engine has been running for at least 180 seconds.

• | The engine speed is at least 1,400 RPM.

• | The vehicle speed is between 40-100 km/h (25-62 mph).

• | The throttle valve is open.

### Conditions for Setting the DTC

The HO2S 1 output does not indicate rich for more than 1.5 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

The scan tool output control feature, Fuel Injector Modification, can be used at idle to check the oxygen sensor performance. Increasing the Fuel Injector Modification Commanded State to 25 percent should cause the HO2S 1 voltage to exceed 800 mV. Decreasing the Fuel Injector Modification Commanded State to -12 percent should cause the HO2S 1 voltage to drop to less than 100 mV. An oxygen sensor that fails to respond accordingly may be faulty or contaminated. When performing the Fuel Injector Modification with the scan tool, the Loop Status will remain Open Loop and the Short Term FT will be fixed at 0 percent and 128 Counts.

Check for any of the following conditions:

• | Any damaged oxygen sensor wiring--The sensor pigtail may be improperly routed and contacting the exhaust system.

• | An incorrect fuel pressure--A condition that causes a lean exhaust can cause DTC P0125 to set. The system will go lean if the fuel pressure is too low. The PCM can compensate for some decrease. However, if the fuel pressure is too low, DTC P0125 may be set. Refer to Fuel System Diagnosis .

• | Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool .

• | Any vacuum leaks--Check for disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, the throttle body, the EGR system, and the crankcase ventilation system.

• | Any exhaust leaks--An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing DTC P0125 to set. Check for exhaust leaks near the HO2S 1.

• | Any fuel contamination--Water, even in small amounts, can be delivered to the fuel injectors. Water can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

An intermittent malfunction may be caused by fault in the HO2S circuit 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 verifies whether the malfunction is a hard failure or an intermittent.

3. This step verifies whether the PCM is able to receive a signal from the HO2S 1. The DMM is used as a low current voltage source taking the place of the HO2S.

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 |

1. Start the engine.
2. Run the engine until the engine reaches a normal operating temperature.
3. Select the HO2S 1 parameter on the scan tool.
4. Snap the throttle.
5. Observe the HO2S 1 parameter.

Does the HO2S 1 voltage vary within the specified range?

200-900 mV

Go to Step 3

Go to Step 4

3 |

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 noted.

Does DTC P0125 set?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Disconnect the HO2S 1 connector.
2. Turn ON the ignition, with the engine OFF.
3. Select the DMM to measure DC millivolts.
4. Place the positive lead of the DMM on battery positive voltage, and the negative lead on the HO2S 1 input circuit terminal on the engine harness side.
5. Observe the HO2S 1 voltage on the scan tool.

Is the voltage more than the specified value?

1155 mV

Go to Step 5

Go to Step 6

5 |

1. Connect a test lamp to battery voltage.
2. Probe the HO2S 1 ground circuit terminal on the engine harness side.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 7

6 |

1. Check for an open or short in the HO2S 1 input circuit between the HO2S 1 and the PCM connector.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 10

Go to Step 9

7 | Repair the open in the HO2S 1 ground circuit between the HO2S 1 and G106. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 10 | --
8 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Is the action complete? | -- | Go to Step 10 | --
9 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 10 | --
10 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 11

Go to Step 2

11 | 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