P0171

DTC P0171: System too Lean (bank 1)

CAUTION: If DTC P0171 has been set, TCL related DTC U1120 is also set After P0171 has been diagnosed, don't forget to erase DTC U1120.

Fuel Trim Circuit
- Refer to DTC P0201 - Injector Circuit - Cylinder, P0203 - Injector Circuit - Cylinder 3, P0205 - Injector Circuit - Cylinder 5.

CIRCUIT OPERATION
- Refer to DTC P0201, P0203, P0205 - Injector Circuit

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

DESCRIPTIONS OF MONITOR METHODS
Right 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:

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 8 g/sec or more.

Judgment Criteria
- Long-term fuel trim has continued to be higher than +125 percent for 5 seconds or
- Short-term fuel trim has continued to be higher than +74 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 8 g/sec or less.

Judgment Criteria
- Long-term fuel trim has continued to be higher than +125 percent for 5 seconds or
- Short-term fuel trim has continued to be higher than +74 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 8 g/sec or more

Judgment Criteria
- Long-term fuel trim has continued to be higher than +125 percent or 5 seconds or
- Short-term fuel trim has continued to be higher than +176 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 8 g/sec or less.

Judgment Criteria
- Long-term fuel trim has continued to be higher than +125 percent or 5 seconds or
- Short-term fuel trim has continued to be higher than +176 percent for 5 seconds

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

Judgment Criteria
- Long-term fuel trim has continued to be +125 percent for 5 seconds or
- Short-term fuel trim has continued to be +250 percent for 5 seconds

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 2 - Fuel Trim Monitor. OBD-II Drive Cycle Pattern Lists

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Mass airflow sensor failed.
- Injector (Number 1, 3, 5) failed.
- Incorrect fuel pressure.
- Air drawn in from gaps in gasket, seals, etc
- Engine coolant temperature sensor failed.
- Intake air temperature sensor failed.
- Barometric pressure sensor failed.
- Manifold absolute pressure sensor failed.
- Exhaust leak.
- Use of incorrect or contaminated fuel.
- Harness damage in right bank injector circuit, or connector damage.
- PCM failed.

DIAGNOSIS

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

STEP 1. Check for exhaust leak.

Q: Are there any abnormalities?

YES: Repair it. Then go to Step 17.

NO: Go to Step 2.

STEP 2. Check for intake system vacuum leak.

Q: Are there any abnormalities?

YES: Repair it. Then go to Step 17.

NO: Go to Step 3.




STEP 3. Using scan tool MB991958, check data list item 12: 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 12, 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 2.0 and 6.0 g/sec
- When 2,500 r/min, between 8.0 and 16.0 g/sec

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

Q: Is the sensor operating properly?

YES: Go to Step 4.

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




STEP 4. Using scan tool MB991958, check data list item 13: 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 13, 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 5,

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




STEP 5. Using scan tool MB991958, check data list item 21: 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 21, 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 6.

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




STEP 6. Using scan tool MB991958, check data list item 25: Barometric Pressure Sensor.

1. Turn the ignition switch to the "ON" position
2. Set scan tool MB991958 to the data reading mode for item 25, Barometric 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)

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

Q: Is the sensor operating properly?

YES: Go to Step 7.

NO: Refer to DTC P2227 - Barometric Pressure Circuit Range/Performance Problem, DTC P2228 - Barometric Pressure Circuit Low Input, DTC P2229 - Barometric Pressure Circuit High Input.




STEP 7. Using scan tool MB991958, check data list item 95: 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 95, 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 8.

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




STEP 8. Check harness connector B-32 at intermediate connector for damage

Q: Is the harness connector in good condition?

YES: Go to Step 9.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 17.







STEP 9. Check the right bank injector resistance at intermediate connector B-32.

1. Disconnect the intermediate connector B-32.
2. Measure the resistance between each male connector side terminal.
a. Measure the resistance between terminal No. 5 and No. 9 at No. 1 cylinder injector.
b. Measure the resistance between terminal No. 9 and No. 10 at No. 3 cylinder injector.
c. Measure the resistance between terminal No. 4 and No. 9 at No. 5 cylinder injector.

- Resistance should be between 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 12.

NO: Go to Step 10.




STEP 10. Check harness connector B-03, B-04, B-01. at right bank injector for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 11.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 17







STEP 11. Check the right bank injector.

1. Remove the intake manifold.
2. Disconnect the right bank injector connector.
3. Measure the resistance between injector side connector terminal No. 1 and No. 2.

Standard value: 10.5 - 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: Repair harness wire between injector intermediate connector and right bank injector connector because of harness damage Then go to Step 17.

NO: Replace the injector Then go to Step 17.




STEP 12. Check harness connector B-23 at PCM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 13.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 17.







STEP 13. Check for harness damage between right bank injector connector and PCM connector.

a. Check the harness wire between injector connector B-01 (terminal No. 2) and PCM connector B-23 (terminal No. 153) at No. 1 cylinder injector.
b. Check the harness wire between injector connector B-03 (terminal No. 2) and PCM connector B-23 (terminal No. 140) at No. 3 cylinder injector.
c. Check the harness wire between injector connector B-04 (terminal No. 2) and PCM connector B-23 (terminal No. 133) at No. 5 cylinder injector.

Q: Is the harness wire in good condition?

YES: Go to Step 14.

NO: Repair it Then go to Step 17.

STEP 14. Check the fuel pressure.

Refer to On-vehicle Service - Fuel Pressure Test.

Q: Is the fuel pressure normal?

YES: Repair it Then go to Step 17.

NO: Go to Step 15.

STEP 15. Check for entry of foreign matter (water, kerosene, etc) into fuel.

Q: Are there any abnormalities?

YES: Replace the fuel Then go to Step 17.

NO: Go to Step 16.




STEP 16. Replace the right bank injector.

1. Replace the right bank injector
2. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 2 - Fuel Trim Monitor. OBD-II Drive Cycle Pattern Lists
3. Check the diagnostic trouble code (DTC)

Q: Is DTC P0171 set?

YES: Replace the PCM. Then go to Step 17.

NO: The inspection is complete.

STEP 17. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 2 - Fuel Trim Monitor. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0171 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.