P0125

Excessive Time to Enter Closed Loop Fuel Control Circuit

Heated Oxygen Sensor (Front) Circuit:

Heated Oxygen Sensor (front) Circuit .

Heated Oxygen Sensor (Front) Circuit:

Heated Oxygen Sensor (front) Circuit .

Injector Circuit:

Injector Circuit.

CIRCUIT OPERATION

Heated Oxygen Sensor (front) Circuit and .
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal 76) or PCM (terminal 71) from the output terminal (terminal 1) of the heated oxygen sensor (front).
- Terminal 2 of the heated oxygen sensor (front) is grounded with ECM (terminal 92) or PCM (terminal 57) .

Injector Circuit.
- The injector power is supplied from the MFI relay (terminal 1).
- The ECM or PCM controls the injector by turning the power transistor in the ECM or PCM "ON" and "OFF."

TECHNICAL DESCRIPTION
- The MFI system reduces exhaust emissions by means of closed loop fuel control.
- The ECM or PCM checks the time taken until closed loop fuel control commences.

DTC SET CONDITIONS

Check Conditions
- Thirty seconds or more have passed since the starting sequence was completed.
- Engine coolant temperature is higher than 81°C (178°F).
- Engine speed is at between about 1,800 and 3,500 r/min.
- Volumetric efficiency is at between 16 and 62 percent.
- The engine is running in the air/fuel ratio feedback zone.
- Monitoring time: 30 seconds.

Judgment Criteria
- Multiport fuel injection system does not enter the closed loop control within about 30 seconds of meeting all criteria above.
- Only one monitor during one drive cycle.

TROUBLESHOOTING HINTS
The most likely causes for this code to be set are:
- Heated oxygen sensor failed.
- Injector failed.
- Fuel pressure regulator failed.
- Fuel pump failed.
- Fuel filter is clogged.
- Intake system vacuum leak.
- Exhaust leak.
- ECM failed.
- PCM failed.

DIAGNOSIS
Required Special Tools:
MB991658: Test Harness Set
MD998464: Test Harness

STEP 1. Check the exhaust leaks.
If no leaks are found, go to Step 2.
If any leak is found, repair it. Then go to Step 11.

STEP 2. Check the intake system vacuum leak.
If no leaks are found, go to Step 3. If any leak is found, repair it. Then go to Step 11.

STEP 3. Check the heated oxygen sensor (front).
1. Disconnect heated oxygen sensor (front) connector C-24 or B-17 and connect special tool MB991658 or MD998464 to the connector on the heated oxygen sensor (front) side.
2. Warm up the engine until engine coolant is 80°C (176°F) or higher.

CAUTION: Be very careful when connecting the jumper wires; incorrect connection can damage the heated oxygen sensor (front).

3. Use the jumper wires to connect terminal 3 or terminal 1 of the heated oxygen sensor (front) connector to the positive battery terminal and terminal 4 or terminal 3 to the negative battery terminal.
4. Connect a digital volt meter between terminal 1 and terminal 2 or terminal 2 and terminal 4 .
5. While repeatedly revving the engine, measure the heated oxygen sensor (front) output voltage.

Standard value: 0.6 - 1.0 V

If within specifications, go to Step 4.
If not within specifications, replace the heated oxygen sensor (front). Then go to Step 11.

STEP 4. Check harness connector C-24 or B-17 at the heated oxygen sensor (front) for damage.
If harness connector C-24 or B-17 is in good condition, go to Step 5.
If harness connector C-24 or B-17 is damaged, repair or replace it.
Refer to Harness Connector Inspection. Then go to Step 11.

STEP 5. Check the injectors.
1. Disconnect each injector connector.
2. Measure resistance between connectors 1 and 2 at each injector.

Standard value: 13 - 16 ohms [at 20°C (68°F)]

If within specifications, go to Step 6.
If not within specifications, replace the faulty injector. Then go to Step 11.

STEP 6. Check harness connectors B-01, B-02, B-05, B-06 at the injector for damage.
If harness connectors B-01, B-02, B-05, B-06 are in good condition, go to Step 7.
If harness connectors B-01, B-02, B-05, B-06 are damaged, repair or replace them.
Refer to Harness Connector Inspection. Then go to Step 11.

STEP 7. Check harness connectors C-49, C-60 at the ECM or harness connector C-50, C-54, C-57 at the PCM for damage.
If harness connectors C-49, C-60 or C-50, C-54, C-57 are in good condition, go to Step 8.
If harness connectors C-49, C-60 or C-50, C-54, C-57 are damaged, repair or replace them.
Refer to Harness Connector Inspection. Then go to Step 11.

STEP 8. Check the harness wire between heated oxygen sensor (front) connector C-24 or B-17 and the ECM connector C-60 or PCM connectors C-54, C-57 .
If the wires between heated oxygen sensor (front) connector
C-24 or B-17 and ECM connector C-60 or PCM connectors C-54, C-57 are not damaged, go to Step 9.

If the wires between heated oxygen sensor (front) connector
C-24 or B-17 and ECM connector C-60 or PCM connectors C-54, C-57 are damaged, repair them. Then go to Step 11.

STEP 9. Check the harness wire between injector connectors B-01, B-02, B-05, B-06 and ECM connector C-49 or PCM connector C-50 . If the wires between injector connectors B-01, B-02, B-05, B-06 and ECM connector C-49 or PCM connector C-50 are not damaged, go to Step 10.
If the wires between injector connectors B-01 B-02, B-05, B-06 and ECM connector C-49 or PCM connector C-50 are damaged, repair them. Then go to Step 11.

STEP 10. Check the fuel pressure.
Refer to Fuel Pressure Test. If correct, replace the ECM or PCM. Then go to Step 11.
If incorrect, repair or replace it. Then go to Step 11.

STEP 11. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to Procedure 6 - Other Monitor.
2. Read the diagnostic trouble code, and confirm that diagnostic trouble code P0125 does not reset.