SFI SYSTEM, Diagnostic DTC:P0171, P0172

DTC Code DTC Name
P0171 System Too Lean (Bank 1)
P0172 System Too Rich (Bank 1)

DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim consists of both short-term and long-term fuel trims.

The short-term fuel trim is fuel compensation that is used to constantly maintain the air fuel ratio at stoichiometric levels. The signal from the air fuel ratio sensor indicates whether the air fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air fuel ratio is rich and an increase in the fuel injection volume if it is lean.

Factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-term fuel trim compensation.

If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is interpreted as a malfunction, and the ECM illuminates the MIL and stores a DTC.

DTC No. DTC Detection Condition Trouble Area
P0171 With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to lean side (2 trip detection logic).

  • Intake system

  • Fuel injector assembly blockage

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leaks from exhaust system

  • Open or short in air fuel ratio sensor (sensor 1) circuit

  • Air fuel ratio sensor (sensor 1)

  • Air fuel ratio sensor heater (sensor 1)

  • Air fuel ratio sensor heater circuit (sensor 1)

  • PCV valve and hose

  • PCV hose connections

  • ECM

  • Wire harness or connector
P0172 With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to rich side (2 trip detection logic).

  • Fuel injector assembly leak or blockage

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Ignition system

  • Fuel pressure

  • Gas leaks from exhaust system

  • Open or short in air fuel ratio sensor (sensor 1) circuit

  • Air fuel ratio sensor (sensor 1)

  • Air fuel ratio sensor heater (sensor 1)

  • Air fuel ratio sensor heater circuit (sensor 1)

  • ECM

  • Wire harness or connector

Tech Tips


  • When DTC P0171 is stored, the actual air fuel ratio is on the lean side. When DTC P0172 is stored, the actual air fuel ratio is on the rich side.

  • If the vehicle runs out of fuel, the air fuel ratio is lean and DTC P0171 may be stored. The MIL is then illuminated.

  • When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and the engine coolant temperature is higher than 75°C [167°F]), the system is functioning normally.

MONITOR DESCRIPTION

Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the ECM's estimated fuel injection volumes also affect the average fuel trim learning value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learning value of the air fuel ratio). If the average fuel trim learning value exceeds the malfunction threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example:

The average fuel trim learning value is +48% or more or -35% or less, the ECM interprets this as a fuel system malfunction.

A002M35E01

CONFIRMATION DRIVING PATTERN

A002MK0E84

  1. Connect the GTS to the DLC3.

  2. Turn the ignition switch to ON and turn the GTS on.

  3. Clear the DTCs Click here.

  4. Turn the ignition switch off.

  5. Turn the ignition switch to ON and turn the GTS on [A].

  6. Start the engine and warm it up until the engine coolant temperature is 75°C (167°F) or higher with all the accessories switched off [B].

  7. With the engine warmed up, idle the engine for 2 minutes or more [C].

  8. Drive the vehicle at a speed between 60 and 100 km/h (37 and 63 mph) for 5 minutes or more [D].

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

  9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes / Pending [E].

  10. Read the Pending DTCs.

    Tech Tips

    If a pending DTC is output, the system is malfunctioning.

WIRING DIAGRAM

Refer to DTC P0102 Click here.

Refer to DTC P2195 Click here.

CAUTION / NOTICE / HINT

Note

Inspect the fuses for circuits related to this system before performing the following inspection procedure.

Tech Tips


  • Read freeze frame data using the GTS. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.

  • A low air fuel ratio sensor voltage could be caused by a rich air fuel mixture. Check for conditions that would cause the engine to run rich.

  • A high air fuel ratio sensor voltage could be caused by a lean air fuel mixture. Check for conditions that would cause the engine to run lean.

  • Sensor 1 refers to the sensor closest to the engine assembly.

  • Sensor 2 refers to the sensor farthest away from the engine assembly.

PROCEDURE


  1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    5. Read the DTCs.

      Result
      Result Proceed to
      DTC P0171 or P0172 is output A
      DTC P0171 or P0172 and other DTCs are output B

      Tech Tips

      If any DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.


    B

    GO TO DTC CHART Click here

    A

  2. CHECK PCV HOSE CONNECTIONS


    1. Check the PCV hose connections Click here.

      OK
      PCV hose is connected correctly and is not damaged.

    NG

    REPAIR OR REPLACE PCV HOSE

    OK

  3. CHECK INTAKE SYSTEM


    1. Check the intake system for vacuum leaks Click here.

      OK
      No leaks in intake system.

      Tech Tips

      Perform "Inspection After Repair" after repairing or replacing the intake system Click here.


    NG

    REPAIR OR REPLACE INTAKE SYSTEM

    OK

  4. PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)


    1. Connect the GTS to the DLC3.

    2. Start the engine.

    3. Turn the GTS on.

    4. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

    5. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Data List / AFS Voltage B1S1 and O2S B1S2.

    6. Perform the Control the Injection Volume for A/F Sensor operation with the engine idling.

    7. Monitor the voltage outputs of the air fuel ratio sensor and the heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the GTS.

      Tech Tips


      • Change the fuel injection volume within the range of -12.5% and 12.5%.

      • The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.

      • If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

      Standard

      GTS Display

      (Sensor)

      		 Injection Volume Status Voltage

      AFS Voltage B1S1

      (Air fuel ratio)

      		 12.5% Rich Below 3.1 V
      -12.5% Lean Higher than 3.4 V

      O2S B1S2

      (Heated oxygen)

      		 12.5% Rich Higher than 0.55 V
      -12.5% Lean Below 0.4 V
      Result

      Status

      AFS Voltage B1S1

      Status

      O2S B1S2

      Air Fuel Ratio Condition and

      Air Fuel Ratio Sensor Condition

      		 Suspected Trouble Area Proceed to
      Lean/Rich Lean/Rich Normal - A
      Lean Lean Actual air fuel ratio lean

      • PCV valve and hose

      • PCV hose connections

      • Fuel injector assembly blockage

      • Gas leak from exhaust system

      • Intake system

      • Fuel pressure

      • Mass air flow meter

      • Engine coolant temperature sensor

      		 A
      Rich Rich Actual air fuel ratio rich

      • Fuel injector assembly leakage or blockage

      • Gas leak from exhaust system

      • Ignition system

      • Fuel pressure

      • Mass air flow meter

      • Engine coolant temperature sensor
      Lean Lean/Rich Air fuel ratio sensor malfunction Air fuel ratio sensor B
      Rich Lean/Rich Air fuel ratio sensor malfunction Air fuel ratio sensor

      Lean: During the Control the Injection Volume for A/F Sensor Active Test, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently higher than 3.4 V, and the heated oxygen sensor output voltages (O2S B1S2) is consistently below 0.4 V.

      Rich: During Control the Injection Volume for A/F Sensor of the Active Test, the AFS Voltage B1S1 is consistently below 3.1 V, and the O2S B1S2 is consistently higher than 0.55 V.

      Lean/Rich: During the Control the Injection Volume for A/F Sensor Active Test, the output voltage of the heated oxygen sensor alternates correctly.


    B

    INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here

    A

  5. READ VALUE USING GTS (COOLANT TEMP)


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Data List / Coolant Temp.

    5. Read the Coolant Temp twice, when the engine is both cold and warmed up.

      Standard
      With cold engine:
      Same as ambient air temperature.
      With warm engine:
      Between 75°C and 100°C (167°F and 212°F).

      Tech Tips

      Perform "Inspection After Repair" after replacing the engine coolant temperature sensor Click here.


    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

    OK

  6. READ VALUE USING GTS (MAF)


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine and ECT / Data List / MAF and Coolant Temp.

    5. Allow the engine to idle until Coolant Temp reaches 75 °C (167°F) or higher.

    6. Read MAF with the engine speed at 3000 rpm.

      Standard
      Between 6.5 gm/sec and 10.5 gm/sec (shift lever: Neutral position, A/C: Off).

    NG

    CHECK HARNESS AND CONNECTOR Click here

    OK

  7. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. CHECK FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leaks.

      OK
      No gas leaks.

      Tech Tips

      Perform "Inspection After Repair" after repairing or replacing the exhaust system Click here.


    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. CHECK FOR SPARK (SPARK TEST)


    1. Perform a spark test Click here.

      Tech Tips


      • If the result of the spark test is normal, proceed to the next step.

      • Perform "Inspection After Repair" after repairing or replacing the ignition system Click here.


    NEXT

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)


    1. Check the injection and volume Click here.

      Tech Tips

      Perform "Inspection After Repair" after replacing the fuel injector assembly Click here.


    OK

    PERFORM CONFIRMATION DRIVING PATTERN Click here

    NG

    REPLACE FUEL INJECTOR ASSEMBLY Click here

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. Inspect the air fuel ratio sensor Click here.

      Tech Tips

      Perform "Inspection After Repair" after replacing the air fuel ratio sensor Click here.


    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

  12. CHECK TERMINAL VOLTAGE (POWER SOURCE OF AIR FUEL RATIO SENSOR)


    1. A002ONJE02
      Text in Illustration
      *a

      Front view of wire harness connector

      (to Air Fuel Ratio Sensor)

      Disconnect the air fuel ratio sensor connector.

    2. Turn the ignition switch to ON.

    3. Measure the voltage according to the value(s) in the table below.

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      C28-2 (+B) - Body ground Ignition switch ON 11 to 14 V

    4. Reconnect the air fuel ratio sensor connector.


    NG

    CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY) Click here

    OK

  13. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)


    1. Disconnect the air fuel ratio sensor connector.

    2. Disconnect the ECM connector.

    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      C28-1 (HA1A) - C111-27 (HA1A) Always Below 1 Ω
      C28-3 (A1A+) - C111-100 (A1A+) Always Below 1 Ω
      C28-4 (A1A-) - C111-132 (A1A-) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      C28-1 (HA1A) or C111-27 (HA1A) - Body ground Always 10 kΩ or higher
      C28-3 (A1A+) or C111-100 (A1A+) - Body ground Always 10 kΩ or higher
      C28-4 (A1A-) or C111-132 (A1A-) - Body ground Always 10 kΩ or higher

    4. Reconnect the ECM connector.

    5. Reconnect the air fuel ratio sensor connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - ECM)

    OK

  14. REPLACE AIR FUEL RATIO SENSOR


    1. Replace the air fuel ratio sensor Click here.

      Tech Tips

      Perform "Inspection After Repair" after replacing the air fuel ratio sensor Click here.


    NEXT

  15. PERFORM CONFIRMATION DRIVING PATTERN


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON and turn the GTS on.

    3. Clear the DTCs Click here.

    4. Turn the ignition switch off.

    5. Turn the ignition switch to ON and turn the GTS on.

    6. Start the engine and warm it up.

    7. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.

    8. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    9. Read the pending DTCs.

      Result
      Result Proceed to
      DTC P0171 or P0172 is output A
      DTC is not output B

    B

    END

    A

  16. CHECK HARNESS AND CONNECTOR


    1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM Click here.

      Tech Tips

      Repair any problems.


    NEXT

  17. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs Click here.

    5. Turn the ignition switch off.

    6. Turn the ignition switch to ON and turn the GTS on.

    7. Start the engine and warm it up.

    8. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.

    9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    10. Read the Pending DTCs.

      Result
      Result Proceed to
      DTC P0171 or P0172 is output A
      DTC is not output B

    B

    END

    A

  18. CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER - ECM)


    1. Disconnect the mass air flow meter connector.

    2. Disconnect the ECM connector.

    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      C3-5 (VG) - C111-137 (VG) Always Below 1 Ω
      C3-4 (E2G) - C111-104 (E2G) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      C3-5 (VG) or C111-137 (VG) - Body ground Always 10 kΩ or higher

    4. Reconnect the mass air flow meter connector.

    5. Reconnect the ECM connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (MASS AIR FLOW METER - ECM)

    OK

  19. REPLACE MASS AIR FLOW METER


    1. Replace the mass air flow meter Click here.

      Tech Tips


      • If the result of the inspection performed in step 6 indicated no problem, proceed to the next step without replacing the mass air flow meter.

      • Perform "Inspection After Repair" after replacing the mass air flow meter Click here.


    NEXT

  20. CHECK WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED


    1. Connect the GTS to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the GTS on.

    4. Clear the DTCs Click here.

    5. Turn the ignition switch off.

    6. Turn the ignition switch to ON and turn the GTS on.

    7. Start the engine and warm it up.

    8. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.

    9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

    10. Read the Pending DTCs.

      Result
      Result Proceed to
      DTC P0171 or P0172 is output A
      DTC is not output B

    A

    REPLACE ECM Click here

    B

    END

  21. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY)


    1. Disconnect the air fuel ratio sensor connector.

    2. Remove the integration relay (EFI MAIN relay) from the engine room No. 1 relay block.

    3. Disconnect the integration relay connector.

    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      C28-2 (+B) - 1B-4 Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      C28-2 (+B) or 1B-4 - Body ground Always 10 kΩ or higher

    5. Reconnect the air fuel ratio sensor connector.

    6. Reconnect the integration relay connector.

    7. Reinstall the integration relay.


    OK

    GO TO ECM POWER SOURCE CIRCUIT Click here

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY)