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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
  • Barometric pressure sensor
  • Throttle position sensor
  • Fuel tank pressure sensor
 
 
DTC SET CONDITIONS
Logic Flow Chart
 
 
Check Conditions
  • Engine coolant temperature is 100°C (212°F) or lower when the engine is started.
  • Intake air temperature is 60°C (140°F) or lower when the engine is started.
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is higher than 76°C (169°F).
Judgment Criterion
  • Long-term fuel trim has continued to be +12.5 percent or higher for 5 seconds.
or
  • Short-term fuel trim has continued to be +10.2 percent or higher 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).
Judgment Criterion
  • Long-term fuel trim has continued to be +12.5 percent or higher for 5 seconds.
or
  • Short-term fuel trim has continued to be +20.3 percent or higher for 5 seconds.
Check Conditions
  • Engine coolant temperature is higher than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
Judgment 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.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • None.
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Linear air-fuel ratio sensor failed.
  • Mass airflow sensor failed.
  • Injector 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.
  • Evaporative emission purge solenoid failed.
  • Use of incorrect or contaminated fuel.
  • Injector circuit harness damage or connector damage.
  • ECM failed.

 
 
DIAGNOSIS
STEP 1. Check for exhaust leak.
Are there any abnormalities?
Repair it. Then go to Step 14.
Go to Step 2.
 
STEP 2. Check for intake system vacuum leak.
Are there any abnormalities?
Repair it. Then go to Step 14.
Go to Step 3.
 
STEP 3. Using scan tool (M.U.T.-IIISE), check data list item 10: Mass Airflow Sensor.
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn off the power supply mode of the electric motor switch 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) Set the vehicle to the continuous idling mode.
(3) Set scan tool (M.U.T.-IIISE) to the data reading mode for item 10, Mass Airflow Sensor.
(4) Warm up the engine.
  • The standard value should be between 880 and 1,280 millivolts.
  • When the engine is revved, the mass airflow rate should increase according to the increase in engine speed.
(5) Turn off the power supply mode of the electric motor switch.
Is the sensor operating properly?
Go to Step 4.
Refer to DTC P0102 - Mass Airflow Circuit Low Input , DTC P0103 - Mass Airflow Circuit High Input .
 
STEP 4. Using scan tool (M.U.T.-IIISE), check data list item 5: Intake Air Temperature Sensor.
(1) Turn on the power supply mode of the electric motor switch.
(2) Set scan tool (M.U.T.-IIISE) 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 off the power supply mode of the electric motor switch.
Is the sensor operating properly?
Go to Step 5.
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 (M.U.T.-IIISE), check data list item 6: Engine Coolant Temperature Sensor.
(1) Turn on the power supply mode of the electric motor switch.
(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 off the power supply mode of the electric motor switch.
Is the sensor operating properly?
Go to Step 6.
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 (M.U.T.-IIISE), check data list item 8: Manifold Absolute Pressure Sensor.
(1) Turn on the power supply mode of the electric motor switch.
(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) Set the vehicle to the continuous idling mode, and warm up the engine.
  • The standard value should be 28.3 - 41.7 kPa (8.36 - 12.31 in.Hg).
  • When the engine is suddenly revved, manifold absolute pressure varies.
(4) Turn off the power supply mode of the electric motor switch.
Is the sensor operating properly?
Go to Step 7.
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 7. Using scan tool (M.U.T.-IIISE), check data list item E1: Linear Air-fuel Ratio Sensor.
(1) Start the engine and run at idle.
(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.
(4) Check the item E1, Linear Air-fuel Ratio Sensor in the data list. Refer to Data List Reference Table .
(5) Turn off the power supply mode of the electric motor switch.
Is the sensor operating properly?
Go to Step 8.
Refer to DTC P0131 - Linear Air-Fuel Ratio Sensor Circuit Low Voltage , DTC P0132 - Linear Air-Fuel Ratio Sensor Circuit High Voltage .
 
STEP 8. Check the evaporative emission purge solenoid.
(1) Disconnect connector, and measure at solenoid side.
(2) Measure the resistance between evaporative emission purge solenoid side connector terminals.
Standard value: 22 - 26 Ω [at 20°C (68°F)]
Is the measured resistance between 22 and 26 Ω [at 20°C (68°F)]?
Go to Step 9.
Replace the evaporative emission purge solenoid. Then go to Step 14.
 
STEP 9. Check the injector.
Refer to Injector Check .
Is the measured resistance normal?
Go to Step 10.
Replace the faulty injector. Then go to Step 14.
 
STEP 10. Check of harness damage between injector connector and ECM connector.
  1. Check the harness wire in INJ1 line between injector connector and ECM connector at No. 1 cylinder injector.
  2. Check the harness wire in INJ2 line between injector connector and ECM connector at No. 2 cylinder injector.
  3. Check the harness wire in INJ3 line between injector connector and ECM connector at No. 3 cylinder injector.
  4. Check the harness wire in INJ4 line between injector connector and ECM connector at No. 4 cylinder injector.
Are the harness wires in good condition?
Go to Step 11.
Repair the connector(s) or wiring harness. Then go to Step 14.
 
STEP 11. Check the fuel pressure.
Refer to Fuel Pressure Test .
Is the fuel pressure normal?
Go to Step 12.
Repair it. Then go to Step 14.
 
STEP 12. Check for entry of foreign matter (water, kerosene, etc.) into fuel.
Are there any abnormalities?
Replace the fuel. Then go to Step 14.
Go to Step 13.
 
STEP 13. Replace the injector.
(1) Replace the injector.
(2) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 .
(3) Check the diagnostic trouble code (DTC).
Is DTC P0171 set?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 14.
The inspection is complete.
 
STEP 14. 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 2 .
(2) Check the diagnostic trouble code (DTC).
Is the DTC P0171 set?
Retry the troubleshooting.
The inspection is complete.