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DTC P0171: System too Lean
 
 
 
 
Fuel Trim Circuit
Refer to, DTC P0261 - Injector Circuit Low input - Cylinder 1 , DTC P0264 - Injector Circuit Low Input - Cylinder 2 , DTC P0267 - Injector Circuit Low Input - Cylinder 3 , DTC P0270 - Injector Circuit Low Input - Cylinder 4 .
 
 
CIRCUIT OPERATION
Refer to, DTC P0261 - Injector Circuit Low input - Cylinder 1 , DTC P0264 - Injector Circuit Low Input - Cylinder 2 , DTC P0267 - Injector Circuit Low Input - Cylinder 3 , DTC P0270 - Injector Circuit Low Input - Cylinder 4 .
 
 
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
  • 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 set 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 1
  • Intake air temperature sensor 2
  • Barometric pressure sensor
  • Throttle position sensor
  • Manifold absolute pressure sensor
  • Boost pressure sensor
 
 
DTC SET CONDITIONS
Logic Flow Chart
 
 
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Monitor disabled stroke is 0 condition.
  • Mass airflow sensor output is 7.68 g/sec or more.
  • Fuel injection mode is MFI-mode.
  • Either engine coolant temperature is lower than 100°C (212°F) when the engine is started. Or, intake air temperature is lower than 60°C (140°F) when the engine is started.
Judgment Criteria
  • Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
  • Short-term fuel trim has continued to be higher than +7.8 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Monitor disabled stroke is 0 condition.
  • Mass airflow sensor output is 7.68 g/sec or more.
  • Fuel injection mode is MFI-mode.
  • 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.
Judgment Criteria
  • Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
  • Short-term fuel trim has continued to be higher than +18.0 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Monitor disabled stroke is 0 condition.
  • Mass airflow sensor output is 7.68 g/sec or less.
  • Fuel injection mode is MFI-mode.
  • Either engine coolant temperature is lower than 100°C (212°F) when the engine is started. Or, intake air temperature is lower than 60°C (140°F) when the engine is started.
Judgment Criteria
  • Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
  • Short-term fuel trim has continued to be higher than +12.9 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Monitor disabled stroke is 0 condition.
  • Mass airflow sensor output is 7.68 g/sec or less.
  • Fuel injection mode is MFI-mode.
  • 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.
Judgment Criteria
  • Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
  • Short-term fuel trim has continued to be higher than +23.0 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Monitor disabled stroke is 0 condition.
  • Mass airflow sensor output is 7.68 g/sec or more.
  • Fuel injection mode is not MFI-mode.
  • Either engine coolant temperature is lower than 100°C (212°F) when the engine is started. Or, intake air temperature is lower than 60°C (140°F) when the engine is started.
Judgment Criteria
  • Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
  • Short-term fuel trim has continued to be higher than +7.8 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Monitor disabled stroke is 0 condition.
  • Mass airflow sensor output is 7.68 g/sec or more.
  • Fuel injection mode is not MFI-mode.
  • 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.
Judgment Criteria
  • Long-term fuel trim has continued to be higher than +12.5 percent for 5 seconds.
  • Short-term fuel trim has continued to be higher than +18.0 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Monitor disabled stroke is 0 condition.
  • Fuel injection mode is MFI-mode.
Judgment Criteria
  • Long-term fuel trim has continued to be +12.5 percent for 2 seconds.
  • Short-term fuel trim has continued to be +25.0 percent for 2 seconds.
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
  • Monitor disabled stroke is 0 condition.
  • Fuel injection mode is not MFI-mode.
Judgment Criteria
  • Long-term fuel trim has continued to be +12.5 percent for 2 seconds.
  • Short-term fuel trim has continued to be +25.0 percent for 2 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • None.
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 8 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )
  • Intake air temperature sensor 1 failed.
  • Engine coolant temperature sensor failed.
  • Manifold absolute pressure sensor failed.
  • Mass airflow sensor failed.
  • Barometric pressure sensor in the ECM failed.
  • Boost pressure sensor failed.
  • Intake air temperature sensor 2 failed.
  • Exhaust leak.
  • Air intake from mass airflow sensor and all components downstream of it.
  • Linear air-fuel sensor failed.
  • Evaporative emission control system failed.
  • Positive crankcase ventilation valve failed.
  • Injector failed.
  • Injector (high pressure) failed.
  • Fuel system related part(s) circuit harness damage, or connector damage.
  • Incorrect fuel pressure.
  • Use of incorrect or contaminated fuel.
  • ECM failed.

 
 
DIAGNOSIS
Preparation to carry out troubleshooting
  • Store the freeze frame data of the DTC P0171.
STEP 1. Using scan tool (M.U.T.-IIISE), read the diagnostic trouble code (DTC).
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-IIISE).
(1) Connect scan tool (M.U.T.-IIISE). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-IIISE) .
(2) Turn the ignition switch to the "ON" position.
(3) Read the DTC.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the diagnostic trouble code other than P0171 set?
Refer to Diagnostic Trouble Code Chart .
Go to Step 2.
 
STEP 2. Using scan tool (M.U.T.-IIISE), check data list item 5: Intake Air Temperature Sensor 1.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool (M.U.T.-IIISE) to the data reading mode for item 5, Intake Air Temperature Sensor 1.
  • The intake air temperature and temperature shown with the scan tool should approximately match.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 3.
Refer to DTC P0112 - Intake Air Temperature Circuit Low Input (sensor 1) , DTC P0113 - Intake Air Temperature Circuit High Input (sensor 1) .
 
STEP 3. Using scan tool (M.U.T.-IIISE), check data list item 6: Engine Coolant Temperature Sensor.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool (M.U.T.-IIISE) 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.
Is the sensor operating properly?
Go to Step 4.
Refer to DTC P0117 - Engine Coolant Temperature Circuit Low Input , DTC P0118 - Engine Coolant Temperature Circuit High Input .
 
STEP 4. Using scan tool (M.U.T.-IIISE), check data list item 8: Manifold Absolute Pressure Sensor.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool (M.U.T.-IIISE) 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).
(3) Start the engine.
  • When the engine is idling, 27 - 47 kPa (8.0 - 13.9 in.Hg).
  • When the engine is suddenly revved, manifold absolute pressure varies.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 5.
Refer to DTC P0107 - Manifold Absolute Pressure Circuit Low Input , DTC P0108 - Manifold absolute pressure circuit high input .
 
STEP 5. Using scan tool (M.U.T.-IIISE), check data list item 10: Mass Airflow Sensor.
(1) Start the engine and run at idle.
(2) Set scan tool (M.U.T.-IIISE) to the data reading mode for item 10, Mass Airflow Sensor.
(3) Warm up the engine to normal operating temperature: 80°C to 95°C (176°F to 203°F).
  • The standard value during idling should be between 800 and 1,120 millivolts.
  • When the engine is revved, the mass airflow rate should increase according to the increase in engine speed.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 6.
Refer to DTC P0102 - Mass Airflow Circuit Low Input , DTC P0103 - Mass Airflow Circuit High Input .
 
STEP 6. Using scan tool (M.U.T.-IIISE), check data list item BB: Barometric Pressure Sensor.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool (M.U.T.-IIISE) to the data reading mode for item BB, 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.
Is the sensor operating properly?
Go to Step 7.
Refer to DTC P2228 - Barometric Pressure Circuit Low Input , DTC P2229 - Barometric Pressure Circuit High Input .
 
STEP 7. Using scan tool (M.U.T.-IIISE), check data list item DE: Intake Air Temperature Sensor 2.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool (M.U.T.-IIISE) to the data reading mode for item DE, Intake Air Temperature Sensor 2.
  • The intake air temperature and temperature shown with the scan tool should approximately match.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 8.
Refer to DTC P0097 - Intake Air Temperature Circuit Low Input (sensor 2) , DTC P0098 - Intake Air Temperature Circuit High Input (sensor 2) .
 
STEP 8. Using scan tool (M.U.T.-IIISE), check data list item 125: Boost Pressure Sensor.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool (M.U.T.-IIISE) to the data reading mode for item 125, Boost 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) Start the engine.
  • When the engine is idling, 70 - 110 kPa (20.7 - 32.4 in.Hg) (Near the atmospheric pressure).
  • When the engine is suddenly revved, intake charge pressure varies.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 9.
Refer to DTC P0237 - Boost Pressure Circuit Low Input , DTC P0238 - Boost Pressure Circuit High Input .
 
STEP 9. Check the positive crankcase ventilation system.
Refer to GROUP 17, Emission Control - Positive Crankcase Ventilation System - Positive Crankcase Ventilation System Check .
Is the positive crankcase ventilation system normal?
Go to Step 10.
Repair it. Then go to Step 30.
 
STEP 10. Check air intake from mass airflow sensor mounting position and all components downstream of it.
Are there any abnormalities?
Repair it. Then go to Step 30.
Go to Step 11.
 
STEP 11. Check for exhaust leak.
Are there any abnormalities?
Repair it. Then go to Step 30.
Go to Step 12.
 
STEP 12. Check installation status of linear air-fuel sensor.
Are there any abnormalities?
Repair it. Then go to Step 30.
Go to Step 13.
 
STEP 13. Using scan tool (M.U.T.-IIISE), check data list item E1: Linear Air-Fuel Ratio Sensor.
(1) Start the engine.
(2) Set scan tool (M.U.T.-IIISE) to the data reading mode for item E1, Linear Air-Fuel Ratio Sensor.
(3) Warm up the engine.
  • When the engine is running at 4,000 r/min is 2.0 volts or less → 3.5 volts or more (After several seconds have elapsed).
  • When the engine is suddenly revved is 2.0 volts or less.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 14.
Refer to DTC P0131 - Linear Air-fuel Ratio Sensor Circuit Low Voltage , DTC P0132 - Linear air-fuel ratio sensor circuit high voltage .
 
STEP 14. Check the evaporative emission purge solenoid.
Refer to GROUP 17, Emission Control - Evaporative Emission Control System - Evaporative Emission Purge Solenoid Check .
Is the evaporative emission purge solenoid normal?
Go to Step 15.
Replace the evaporative emission purge solenoid. Then go to Step 30.
 
STEP 15. Check of harness damage in PURG line between evaporative emission purge solenoid connector and ECM connector.
Is the harness wire in good condition?
Go to Step 16.
Repair the connector(s) or wiring harness. Then go to Step 30.
 
STEP 16. Check of harness damage in power supply line between MFI relay connector and evaporative emission purge solenoid connector.
Is the harness wire in good condition?
Go to Step 17.
Repair the connector(s) or wiring harness. Then go to Step 30.
 
STEP 17. Check the vacuum hose.
Refer to GROUP 17, Emission Control - Vacuum Hose - Vacuum Hose Check .
Are the vacuum hoses normal?
Go to Step 18.
Replace any damaged hose. Then go to Step 30.
 
STEP 18. Check the evaporative emission control system.
Refer to GROUP 17, Emission Control - Evaporative Emission Control System - Purge Control System Check (purge flow check) .
Is the evaporative emission control system normal?
Go to Step 19.
Repair it. Then go to Step 30.
 
STEP 19. Check the evaporative emission canister.
(1) Visually check for cracks or other leaks in the evaporative emission canister.
(2) Connect a hand vacuum pump to the evaporative emission canister and plug the other nipples.
(3) Apply a pressure on the hand vacuum pump, and confirm that air is maintained.
(4) Disconnect the hand vacuum pump and remove the plugs.
Is the evaporative emission canister in good condition?
Go to Step 20.
Replace the evaporative emission canister. Then go to Step 30.
 
STEP 20. Check the evaporative emission ventilation solenoid.
Refer to GROUP 17, Emission Control - Evaporative Emission Canister and Fuel Tank Pressure Relief Valve - Inspection .
Is the evaporative emission ventilation solenoid normal?
Go to Step 21.
Replace the evaporative emission canister and evaporative emission ventilation solenoid assembly. Then go to Step 30.
 
STEP 21. Check the injector.
Refer to Injector Check .
Is the measured resistance normal?
Go to Step 22.
Replace the faulty injector. Then go to Step 30.
 
STEP 22. Check of harness damage in INJ1, INJ2, INJ3, INJ4 line between injector connectors and ECM connector.
Are the harness wire in good condition?
Go to Step 23.
Repair the connector(s) or wiring harness. Then go to Step 30.
 
STEP 23. Check of harness damage in power supply line between MFI relay connector and injector connectors.
Are the harness wire in good condition?
Go to Step 24.
Repair the connector(s) or wiring harness. Then go to Step 30.
 
STEP 24. Check the injector (high pressure).
Refer to Injector Check .
Is the measured resistance normal?
Go to Step 25.
Replace the faulty injector (high pressure). Then go to Step 30.
 
STEP 25. Check of harness damage in DI-1, DI-2, DI-3, DI-4 line between injector (high pressure) connectors and ECM connector.
Are the harness wire in good condition?
Go to Step 26.
Repair the connector(s) or wiring harness. Then go to Step 30.
 
STEP 26. Check of harness damage in DI+1, DI+2, DI+3, DI+4 line between injector (high pressure) connectors and ECM connector.
Are the harness wire in good condition?
Go to Step 27.
Repair the connector(s) or wiring harness. Then go to Step 30.
 
STEP 27. Check the fuel pressure.
Refer to Fuel Pressure Test .
Is the fuel pressure normal?
Go to Step 28.
Repair it. Then go to Step 30.
 
STEP 28. Check for entry of foreign matter (water, diesel fuel, etc.) into fuel.
Are there any abnormalities?
Replace the fuel. Then go to Step 30.
Go to Step 29.
 
STEP 29. After checking stored freeze frame data, check DTC again.
  • If DTC P0171 is set while the vehicle is idling, let the vehicle idle for more than 20 minutes.
  • If DTC P0171 is set while the vehicle is running, let the vehicle run with the same conditions of the freeze frame data, such as the vehicle speed, the crank angle sensor and the coolant temperature sensor, for more than 10 minutes.
Is DTC P0171 set?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 30.
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
 
STEP 30. 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 - Pattern 8 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0171 set?
Retry the troubleshooting.
The inspection is complete.