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P0174

DTC P0174: System too Lean (bank 2)

Fuel Trim Circuit

Injector Circuit-Cylinder 2 (Part 1):




Injector Circuit-Cylinder 2 (Part 2):




Injector Circuit-Cylinder 4 (Part 1):




Injector Circuit-Cylinder 4 (Part 2):




Injector Circuit-Cylinder 6 (Part 1):




Injector Circuit-Cylinder 6 (Part 2):






CIRCUIT OPERATION

Injector Circuit - Cylinder 2
- The injector power is supplied from the injector relay (terminal No. 3).
- The ECM controls the injector by turning the power transistor in the ECM "ON" and "OFF".

Injector Circuit - Cylinder 4
- The injector power is supplied from the injector relay (terminal No. 3).
- The ECM controls the injector by turning the power transistor in the ECM "ON" and "OFF".

Injector Circuit - Cylinder 6
- The injector power is supplied from the injector relay (terminal No. 3).
- The ECM controls the injector by turning the power transistor in the ECM "ON" and "OFF".

TECHNICAL DESCRIPTION
- If a malfunction occurs in the fuel system, the fuel trim value becomes too large.
- The ECM checks whether the fuel trim value is within a specified range.

DESCRIPTIONS OF MONITOR METHODS
Left bank air/fuel learning value (long time fuel trim) and air/fuel feedback integral value (short time fuel trim) are too lean.

MONITOR EXECUTION
Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Misfire monitor

Sensor (The sensor below is determined to be normal)
- Mass airflow sensor
- Engine coolant temperature sensor
- Intake air temperature sensor
- Barometric pressure sensor
- Throttle position sensor

DTC SET CONDITIONS

Logic Flow Chart:






Check Conditions
- Engine coolant temperature is lower than 100 °C (212 °F) when the engine is started.
- Intake air temperature is lower than 60 °C (140 °F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 76 °C (169 °F).
- Mass airflow sensor output is 12 g/sec or more.

Judgement Criterion
- Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.

or

- Short-term fuel trim has continued to be higher than +7.4 percent for 5 seconds.

Check Conditions
- Engine coolant temperature is lower than 100 °C (212 °F) when the engine is started.
- Intake air temperature is lower than 60 °C (140 °F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 76 °C (169 °F).
- Mass airflow sensor output is 12 g/sec or less.

Judgement Criterion
- Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.

or

- Short-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.

Check Conditions
- Engine coolant temperature is higher than 100 °C (212 °F) when the engine is started.
- Intake air temperature is higher than 60 °C (140 °F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 76 °C (169 °F).
- Mass airflow sensor output is 12 g/sec or more.

Judgement Criterion
- Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.

or

- Short-term fuel trim has continued to be higher than +17.6 percent for 5 seconds.

Check Conditions
- Engine coolant temperature is higher than 100 °C (212 °F) when the engine is started.
- Intake air temperature is higher than 60 °C (140 °F) when the engine is started.
- Under the closed loop air/fuel ratio control.
- Engine coolant temperature is higher than 76 °C (169 °F).
- Mass airflow sensor output is 12 g/sec or less.

Judgement Criterion
- Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.

or

- Short-term fuel trim has continued to be higher than +22.3 percent for 5 seconds.

Check Conditions
- Engine coolant temperature is higher than 76 °C (169 °F).
- Under the closed loop air/fuel ratio control.

Judgement Criterion
- Long-term fuel trim has continued to be +12.5 percent for 2 seconds.

or

- Short-term fuel trim has continued to be +25.0 percent for 2 seconds.

OBD-II DRIVE CYCLE PATTERN
Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 22. OBD-II Drive Cycle

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Mass airflow sensor failed.
- Injector (Number 2, 4, 6) failed.
- Incorrect fuel pressure.
- Air drawn in from gaps in gasket, seals, etc.
- Engine coolant temperature sensor failed.
- Intake air temperature sensor failed.
- Manifold absolute pressure sensor failed.
- Exhaust leak.
- Use of incorrect or contaminated fuel.
- Harness damage.
- Connector damage.
- ECM failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A

STEP 1. Using scan tool MB991958, check data list item 10: Mass Airflow Sensor.






CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991958 to the data reading mode for item 10, Mass Airflow Sensor.
4. Warm up the engine to normal operating temperature: 80 °C to 95 °C (176 °F to 203 °F).
- When idling, between 1,350 and 1,670 millivolts.
- When 2,500 r/min, between 1,620 and 2,020 millivolts.

5. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES : Go to Step 2.

NO : Refer to MFI DTC P0101-Mass Airflow Circuit Range/Performance Problem, P0101 DTC P0102-Mass Airflow Circuit Low Input, P0102 DTC P0103-Mass Airflow Circuit High Input. P0103

STEP 2. Using scan tool MB991958, check data list item 5: Intake Air Temperature Sensor.

1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991958 to the data reading mode for item 5, Intake Air Temperature Sensor.
- The intake air temperature and temperature shown with the scan tool should approximately match.

3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES : Go to Step 3.

NO : Refer to MFI DTC P0111-Intake Air Temperature Circuit Range/Performance Problem, P0111 DTC P0112-Intake Air Temperature Circuit Low Input, P0112 DTC P0113-Intake Air Temperature Circuit High Input. P0113

STEP 3. Using scan tool MB991958, check data list item 6: Engine Coolant Temperature Sensor.

1. Turn the ignition switch to the "ON" position.
2. Set scan tool MB991958 to the data reading mode for item 6, Engine Coolant Temperature Sensor.
- The engine coolant temperature and temperature shown with the scan tool should approximately match.

3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES : Go to Step 4.

NO : Refer to MFI DTC P0116-Engine Coolant Temperature Circuit Range/Performance Problem, P0116 DTC P0117-Engine Coolant Temperature Circuit Low Input, P0117 DTC P0118-Engine Coolant Temperature Circuit High Input. P0118

STEP 4. Using scan tool MB991958, check data list item 8: Manifold Absolute Pressure Sensor.

1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991958 to the data reading mode for item 8, Manifold Absolute Pressure Sensor.
- When altitude is 0 m (0 foot), 101 kPa (29.8 in.Hg).
- When altitude is 600 m (1,969 feet), 95 kPa (28.1 in.Hg).
- When altitude is 1,200 m (3,937 feet), 88 kPa (26.0 in.Hg).
- When altitude is 1,800 m (5,906 feet), 81 kPa (23.9 in.Hg).

4. Start the engine.
- When the engine is idling, 16 - 36 kPa (4.7 - 10.6 in.Hg).
- When the engine is suddenly revved, manifold absolute pressure varies.

5. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES : Go to Step 5.

NO : Refer to MFI DTC P0106-Manifold Absolute Pressure Circuit Range / Performance Problem, P0106 DTC P0107-Manifold Absolute Pressure Circuit Low Input, P0107 DTC P0108 Manifold Absolute Pressure Circuit High Input. P0108

STEP 5. Check the fuel pressure.

Refer to MFI On-vehicle Service-Fuel Pressure Test. Testing and Inspection

Q: Is the fuel pressure normal?

YES : Go to Step 6.

NO : Repair it. Then go to Step 13.

STEP 6. Check for harness connector B-115, B-116, B-120 at the left bank injector and harness connector B-10 at ECM for damage.

Q: Is the harness connector in good condition?

YES : Then go to Step 7.

NO : Repair it. Refer to General (Electrical), Harness Connector Inspection. Then go to Step 13.

STEP 7. Check the left bank injector.

1. Disconnect the left bank injector connector B-115, B-116, B-120.




2. Measure the resistance between injector side connector terminal No. 1 and No. 2.
- Standard value: 10.5 and 13.5 ohms [at 20 °C (68 °F)]

Q: Is the measured resistance between 10.5 and 13.5 ohms [at 20 °C (68 °F)]?

YES : Go to Step 8.

NO : Replace the injector. Then go to Step 13.

STEP 8. Check for harness between the left bank injector connector B-115, B-116, B-120 and the ECM connector B-10.

1. Disconnect the left bank injector connector B-115, B-116, B-120 and the ECM connector B-10.




2. Measure the resistance between the left bank injector connector B-115, B-116, B-120 and the ECM connector B-10.
- Should be less than 2 ohms.
a. Connector B-115 (terminal No. 2) and connector B-10 (terminal No. 51) at No. 6 cylinder injector.
b. Connector B-116 (terminal No. 2) and connector B-10 (terminal No. 19) at No. 4 cylinder injector.
c. Connector B-120 (terminal No. 2) and connector B-10 (terminal No. 3) at No. 2 cylinder injector.

Q: Is the harness wire in good condition?

YES : Go to Step 9.

NO : Repair it. Refer to General (Electrical), Harness Connector Inspection. Then go to Step 13.

STEP 9. Check for exhaust leak.

Q: Are there any abnormalities?

YES : Repair it. Then go to Step 13.

NO : Go to Step 10.

STEP 10. Check for intake system vacuum leak.

Q: Are there any abnormalities?

YES : Repair it. Then go to Step 13.

NO : Go to Step 11.

STEP 11. Check for entry of foreign matter (water, kerosene, etc.) into fuel.

Q: Are there any abnormalities?

YES : Replace the fuel. Then go to Step 13.

NO : Go to Step 12.

STEP 12. Replace the left bank injector.

1. Replace the left bank injector.
2. Carry out a test drive with the drive cycle pattern. Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 22. OBD-II Drive Cycle
3. Check the diagnostic trouble code (DTC).

Q : Is DTC P0174 set?

YES : Replace the ECM. When the ECM is replaced, register the ID code. Refer to Diagnosis-ID Codes Registration Judgment Table [Vehicles with KOS] or Diagnosis-ID Codes Registration Judgment Table [Vehicles with WCM]. Then go to Step 13.

NO : The inspection is complete.

STEP 13. Test the OBD-II drive cycle.

1. Carry out a test drive with the drive cycle pattern. Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 22. OBD-II Drive Cycle
2. Check the diagnostic trouble code (DTC).

Q : Is DTC P0174 set?

YES : Retry the troubleshooting.

NO : The inspection is complete.
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