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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 .
 
 
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 .
 
 
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 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 less than 100°C (212°F) when the engine is started.
  • Intake air temperature is less than 60°C (140°F) when the engine is started.
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is more than 76°C (169°F).
  • Mass airflow sensor output is more than 6 g/sec.
Judgment Criterion
  • Long-term fuel trim is more than +12.5 percent for 5 seconds.
or
  • Short-term fuel trim is more than +7.0 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is less than 100°C (212°F) when the engine is started.
  • Intake air temperature is less than 60°C (140°F) when the engine is started.
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is more than 76°C (169°F).
  • Mass airflow sensor output is less than 6 g/sec.
Judgment Criterion
  • Long-term fuel trim is more than +12.5 percent for 5 seconds.
or
  • Short-term fuel trim is more than +12.1 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is more than 100°C (212°F) when the engine is started.
  • Intake air temperature is more than 60°C (140°F) when the engine is started.
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is more than 76°C (169°F).
  • Mass airflow sensor output is more than 6 g/sec.
Judgment Criterion
  • Long-term fuel trim is more than +12.5 percent for 5 seconds.
or
  • Short-term fuel trim is more than +17.2 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is more than 100°C (212°F) when the engine is started.
  • Intake air temperature is more than 60°C (140°F) when the engine is started.
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is more than 76°C (169°F).
  • Mass airflow sensor output is less than 6 g/sec.
Judgment Criterion
  • Long-term fuel trim is more than +12.5 percent for 5 seconds.
or
  • Short-term fuel trim is more than +22.3 percent for 5 seconds.
Check Conditions
  • Engine coolant temperature is more than 76°C (169°F).
  • Under the closed loop air/fuel ratio control.
Judgment Criterion
  • Long-term fuel trim is +12.5 percent for 2 seconds.
or
  • Short-term fuel trim is +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 20 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • 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.
  • Use of incorrect or contaminated fuel.
  • Harness damage in injector circuit or connector damage.
  • ECM failed.

 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite main harness A
  • MB992747: V.C.I.-Lite USB cable short
  • MB992748: V.C.I.-Lite USB cable long
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: Vehicles Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
STEP 1. Check for exhaust leak.
Are there any abnormalities?
Repair it. Then go to Step 12.
Go to Step 2.
 
STEP 2. Check for intake system vacuum leak.
Are there any abnormalities?
Repair it. Then go to Step 12.
Go to Step 3.
 
STEP 3. Using scan tool (M.U.T.-III), check data list item 10: Mass Airflow Sensor.
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
(1) Connect scan tool (M.U.T.-III). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-III) .
(2) Start the engine and run at idle.
(3) Set scan tool (M.U.T.-III) 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 760 and 1,080 millivolts.
  • When 2,500 r/min, between 1,130 and 1,530 millivolts.
(5) Turn the ignition switch to the "LOCK" (OFF) position.
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.-III), check data list item 5: Intake Air Temperature Sensor.
(1) Turn the ignition switch to the "ON" position.
(2) Set scan tool (M.U.T.-III) 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.
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.-III), 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.-III) 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 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.-III), 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.-III) 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.
  • Warm up the engine. When the engine is idling, 22 - 42 kPa (6.5 - 12.4 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 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. Check the injector.
  • Injector check (Refer to ).
Is the measured resistance normal?
Go to Step 8.
Replace the faulty injector. Then go to Step 12.
 
STEP 8. 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.
Are the harness wires in good condition?
Go to Step 9.
Repair the connector(s) or wiring harness. Then go to Step 12.
 
STEP 9. Check the fuel pressure.
Refer to, Fuel Pressure Test .
Is the fuel pressure normal?
Go to Step 10.
Repair it. Then go to Step 12.
 
STEP 10. Check for entry of foreign matter (water, diesel fuel, etc.) into fuel.
Are there any abnormalities?
Replace the fuel. Then go to Step 12.
Go to Step 11.
 
STEP 11. 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 20 .
(3) Check the diagnostic trouble code (DTC).
Is DTC P0171 set?
Replace the ECM (Refer to, Removal and Installation ). Then go to Step 12.
The inspection is complete.
 
STEP 12. 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 20 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0171 set?
Retry the troubleshooting.
The inspection is complete.