SFI SYSTEM (w/o EGR 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 duration. The fuel trim consists of both the short-term and long-term fuel trim.

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 trim 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

  • Mass air flow meter sub-assembly

  • 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)

  • PCV valve and hose

  • PCV hose connections

  • Wire harness or connector

  • ECM
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

  • Mass air flow meter sub-assembly

  • 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)

  • Wire harness or connector

  • ECM

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 then illuminates.

  • 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 fuel injection volumes estimated by the ECM also affect the average fuel trim learned value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learned value of the air fuel ratio). If the average fuel trim learned value exceeds the malfunction thresholds, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example:

The average fuel trim learning value is +52% or more, or -35% or less, the ECM interprets this as a fuel system malfunction.

A003XR6E67

MONITOR STRATEGY

Required Sensors/Components Fuel system
Frequency of Operation Continuous

TYPICAL ENABLING CONDITIONS

Fuel system status Closed-loop
Auxiliary battery voltage 11 V or higher
Either of the following conditions is set 1 or 2
1. Engine speed Less than 1100 rpm
2. Intake air amount per revolution 0.12 g/rev or more

TYPICAL MALFUNCTION THRESHOLDS

Purge-cut Executing
Either of the following conditions is met 1 or 2
1. Average between short-term fuel trim and long-term fuel trim 52% or more (varies with engine coolant temperature)
2. Average between short-term fuel trim and long-term fuel trim -35% or less (varies with engine coolant temperature)

CONFIRMATION DRIVING PATTERN

A003VJCE78

  1. Connect the intelligent tester to the DLC3.

  2. Turn the power switch on (IG) and turn the tester on.

  3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation).

  4. Turn the power switch off and wait for at least 30 seconds.

  5. Turn the power switch on (IG) and turn the tester on [A].

  6. Put the engine in inspection mode (maintenance mode) Click here.

  7. 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].

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

  9. Drive the vehicle at between 75 and 120 km/h (47 and 75 mph) for 5 minutes or more [D].

    CAUTION:

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

  10. Enter the following menus: Powertrain / Engine and ECT / DTC.

  11. Read the pending DTCs [E].

    Tech Tips


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

WIRING DIAGRAM

Refer to DTC P2195 for the air fuel ratio sensor circuit Click here.

Refer to DTC P0102 for the mass air flow meter sub-assembly circuit Click here.

INSPECTION PROCEDURE

Tech Tips

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor function can help to determine whether the air fuel ratio sensor, heated oxygen sensor and other potential trouble areas are malfunctioning.

The following instructions describe how to conduct the Control the Injection Volume for A/F Sensor operation using the intelligent tester.


  1. Connect the intelligent tester to the DLC3.

  2. Turn the power switch on (IG) and turn the tester on.

  3. Put the engine in inspection mode (maintenance mode) Click here.

  4. Start the engine.

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

    Tech Tips

    During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, warm up the engine after charging control has completed.

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

  7. Perform the Active Test operation with the engine in an idling.

  8. Monitor the voltage outputs of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.

    Tech Tips


    • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.

    • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

    Tester 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

    Note

    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.

    Case Air Fuel Ratio Sensor (Sensor 1) Output Voltage Heated Oxygen Sensor (Sensor 2) Output Voltage Main Suspected Trouble Area
    1 A003Z7YE11 A003WEDE08 A003Z7YE11 A003YKNE06 -
    2 A003Z7YE11 A003YHUE01 A003Z7YE11 A003YKNE06

    • Air fuel ratio sensor

    • Air fuel ratio sensor heater

    • Air fuel ratio sensor circuit
    3 A003Z7YE11 A003WEDE08 A003Z7YE11 A003YHUE01

    • Heated oxygen sensor

    • Heated oxygen sensor heater

    • Heated oxygen sensor circuit
    4 A003Z7YE11 A003YHUE01 A003Z7YE11 A003YHUE01

    • Fuel injector assembly

    • Fuel pressure

    • Gas leak from exhaust system (air fuel ratio extremely rich or lean)

    • Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the air fuel ratio and heated oxygen sensors.

    • To display the graph, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Data List / All Data / AFS Voltage B1S1 and O2S B1S2.

Note

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

Tech Tips


  • Read freeze frame data using the intelligent tester. 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 intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

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

    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. Inspect the PCV hose connections Click here.

      OK
      PCV valve and 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.

    NG

    REPAIR OR REPLACE INTAKE SYSTEM

    OK

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

    4. Put the engine in inspection mode (maintenance mode) Click here.

    5. Start the engine.

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

      Tech Tips

      During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, warm up the engine after charging control has completed.

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

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

    9. Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.

      Tech Tips


      • The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 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
      Tester 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 of AFS Voltage B1S1 Status of 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 leaks from exhaust system

      • Intake system

      • Fuel pressure

      • Mass air flow meter sub-assembly

      • Engine coolant temperature sensor

      		 A
      Rich Rich Actual air fuel ratio rich

      • Fuel injector assembly leakage or blockage

      • Gas leaks from exhaust system

      • Ignition system

      • Fuel pressure

      • Mass air flow meter sub-assembly

      • Engine coolant temperature sensor

      		 A
      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 B

      • 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 voltage (O2S B1S2) is consistently below 0.4 V.

      • Rich: During the Control the Injection Volume for A/F Sensor 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 air fuel ratio sensor and heated oxygen sensor alternates correctly.

      Tech Tips

      Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2] Click here.


    B

    INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here

    A

  5. READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

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

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

      Standard
      Tester Display Condition Specified Condition
      Coolant Temp Cold engine Same as ambient air temperature
      Warm engine Between 75 and 100°C (167 and 212°F)

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

    OK

  6. READ VALUE USING INTELLIGENT TESTER (MAF)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

    4. Put the engine in inspection mode (maintenance mode) Click here.

    5. Start the engine.

    6. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / MAF, Coolant Temp and Engine Speed.

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

    8. Read MAF with the engine speed at 2500 rpm.

      Tech Tips

      During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, read the Data List after charging control has completed.

      Standard
      Tester Display Condition Specified Condition
      MAF

      Park (P) has been selected

      A/C: Off

      Engine Speed: 2500 rpm

      		 Between 4.5 gm/sec. and 8.5 gm/sec.

    NG

    CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION) 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.

    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.

      • If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using the intelligent tester. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).


    NEXT

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)


    1. Check the injection and volume.

      Tech Tips


      • Refer to the fuel injector assembly inspection procedure Click here.

      • If the injectors malfunction, engine misfire may occur. The misfire count can be read using the intelligent tester. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).

      Result
      Result Proceed to
      NG A
      OK B

    B

    CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172) Click here

    A

    REPLACE FUEL INJECTOR ASSEMBLY Click here

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. Inspect 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. A003VD4E12
      Text in Illustration
      *a

      Front view of wire harness connector

      (to Air Fuel Ratio Sensor (Sensor 1))

      Disconnect the air fuel ratio sensor connector.

    2. Turn the power switch on (IG).

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

      Standard Voltage
      Tester Connection Condition Specified Condition
      D23-2 (+B) - Body ground Power switch on (IG) 11 to 14 V

    NG

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

    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
      Tester Connection Condition Specified Condition
      D23-1 (HA1A) - D27-18 (HA1A) Always Below 1 Ω
      D23-3 (A1A+) - D27-103 (A1A+) Always Below 1 Ω
      D23-4 (A1A-) - D27-126 (A1A-) Always Below 1 Ω
      D23-1 (HA1A) or D27-18 (HA1A) - Body ground Always 10 kΩ or higher
      D23-3 (A1A+) or D27-103 (A1A+) - Body ground Always 10 kΩ or higher
      D23-4 (A1A-) or D27-126 (A1A-) - Body ground Always 10 kΩ or higher

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  14. REPLACE AIR FUEL RATIO SENSOR


    1. Replace the air fuel ratio sensor Click here.


    NEXT

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

    4. Clear the DTCs Click here.

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

    6. Enter the following menus: Powertrain / Engine and ECT / DTC / Pending.

    7. 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 (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION)


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

      Tech Tips

      Repair any problems.


    NEXT

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

    4. Clear the DTCs Click here.

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

    6. Enter the following menus: Powertrain / Engine and ECT / DTC / Pending.

    7. 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 SUB-ASSEMBLY - ECM)


    1. Disconnect the mass air flow meter sub-assembly connector.

    2. Disconnect the ECM connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      D5-5 (VG) - D27-94 (VG) Always Below 1 Ω
      D5-4 (E2G) - D27-117 (E2G) Always Below 1 Ω
      D5-5 (VG) or D27-94 (VG) - Body ground Always 10 kΩ or higher

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  19. REPLACE MASS AIR FLOW METER SUB-ASSEMBLY


    1. Replace the mass air flow meter sub-assembly 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 sub-assembly.


    NEXT

  20. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED


    1. Connect the intelligent tester to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the tester on.

    4. Clear the DTCs Click here.

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

    6. Enter the following menus: Powertrain / Engine and ECT / DTC / Pending.

    7. Read the pending DTCs.

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

    B

    REPLACE ECM Click here

    A

    END