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 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 sets 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

  • EGR valve assembly

  • 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

  • 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)

  • EGR valve assembly

  • ECM

  • Wire harness or connector

Tech Tips


  • When DTC P0171 is set, the actual air fuel ratio is on the lean side. When DTC P0172 is set, 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 set. The MIL is 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 more than 75°C (167°F)), the system is functioning normally.

MONITOR DESCRIPTION

Under closed-loop fuel control, fuel injection volumes that deviates 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 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:

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

A003TIDE32

WIRING DIAGRAM

Air fuel ratio sensor circuit: Refer to DTC P2195 Click here.

Mass air flow meter sub-assembly circuit: Refer to DTC P0102 Click here.

INSPECTION PROCEDURE

Tech Tips

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor 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 Click here.

  4. Start the engine.

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

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

  7. Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).

  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 25%.

    • 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)

    		 +25% Rich Less than 3.1 V

    AFS Voltage B1S1

    (Air fuel ratio)

    		 -12.5% Lean More than 3.4 V

    O2S B1S2

    (Heated oxygen)

    		 +25% Rich More than 0.55 V

    O2S B1S2

    (Heated oxygen)

    		 -12.5% Lean Less than 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 A003UKNE12 A003UPYE01 -
    2 A003S3KE06 A003UPYE01

    • Air fuel ratio sensor

    • Air fuel ratio sensor heater

    • Air fuel ratio sensor circuit
    3 A003UKNE12 A003S3KE07

    • Heated oxygen sensor

    • Heated oxygen sensor heater

    • Heated oxygen sensor circuit

    • Exhaust gas leaks
    4 A003S3KE06 A003S3KE06

    • Fuel pressure

    • Exhaust gas leaks

      (Air fuel ratio extremely lean or rich)

    • 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 / 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


  • 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.

  • 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.

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. 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.

    NG

    REPAIR OR REPLACE INTAKE SYSTEM

    OK

  4. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME)


    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 Click here.

    4. Start the engine.

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

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

    7. Perform the Control the Injection Volume operation with the engine idling.

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

      Tech Tips


      • Change the fuel injection volume within the range of -12.0% to +12.0%. The injection volume can be changed in fine gradations.

      • 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.

      Standard

      Tester Display

      (Sensor)

      		 Injection Volume Status Voltage

      AFS Voltage B1S1

      (air fuel ratio)

      		 +12% Rich Less than 3.1 V
      -12% Lean More than 3.4 V

      O2S B1S2

      (heated oxygen)

      		 +12% Rich More than 0.55 V
      -12% Lean Less than 0.4 V
      Result

      Status

      AFS Voltage B1S1

      Status

      O2S B1S2

      Air Fuel Ratio Condition and

      Air Fuel Ratio Sensor Condition

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

      • 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

      • Manifold absolute pressure sensor

      • Engine coolant temperature sensor

      • EGR valve assembly
      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

      • Manifold absolute pressure sensor

      • Engine coolant temperature sensor

      • EGR valve assembly

      		 A
      Lean Lean/Rich Air fuel ratio sensor malfunction -

      • Air fuel ratio sensor

      • EGR valve assembly

      		 B
      Rich Lean/Rich Air fuel ratio sensor malfunction - Air fuel ratio sensor

      Lean: During Control the Injection Volume, the air fuel ratio sensor output voltage (AFS Voltage) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.

      Rich: During Control the Injection Volume, the AFS Voltage is consistently less than 3.1 V, and the O2S is consistently more than 0.55 V.

      Lean/Rich: During Control the Injection Volume of the Active Test, the output voltage of the 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 value
      With cold engine: Same as ambient air temperature.
      With warm engine: Between 75 to 100°C (167 to 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 Click here.

    5. Start the engine.

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

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

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

      Standard
      Between 4.5 and 8.5 gm/sec. (Shift lever: N; 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.

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. CHECK FOR SPARK AND IGNITION


    1. Perform spark test Click here.

      CAUTION:

      Always disconnect all fuel injector assembly connectors.

      Note

      Do not crank the engine for more than 2 seconds.

      OK
      Spark jumps across electrode gap.

    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)


    1. Check the injection and volume Click here.

      Result
      Result Proceed to
      NG A
      OK B

    B

    PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION) 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 AIR FUEL RATIO SENSOR (POWER SOURCE VOLTAGE)


    1. A003SC3E06
      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 power switch on (IG).

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      B97-2 (+B) - Body ground Power switch on (IG) 11 to 14 V

    4. Reconnect the air fuel ratio sensor connector.


    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - NO. 2 INTEGRATION 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 (Check for Open)
      Tester Connection Condition Specified Condition
      B97-1 (HA1A) - B31-18 (HA1A) Always Below 1 Ω
      B97-3 (A1A+) - B31-103 (A1A+) Always Below 1 Ω
      B97-4 (A1A-) - B31-126 (A1A-) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      B97-1 (HA1A) or B31-18 (HA1A) - Body ground Always 10 kΩ or higher
      B97-3 (A1A+) or B31-103 (A1A+) - Body ground Always 10 kΩ or higher
      B97-4 (A1A-) or B31-126 (A1A-) - Body ground Always 10 kΩ or higher

    4. Reconnect the air fuel ratio sensor connector.

    5. Reconnect the ECM 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.


    NEXT

  15. PERFORM CONFIRMATION DRIVING PATTERN


    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. Turn the power switch off.

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

    7. Put the engine in inspection mode Click here.

    8. Start the engine and warm it up.

    9. With the engine warmed up, idle the engine for 2 minutes or more.

    10. Drive the vehicle at between 75 and 120 km/h (45 and 75 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes or more.

      CAUTION:

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

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

    12. Check the pending DTCs.

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

    B

    END

    A

  16. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION)


    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 and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

      Tech Tips

      The A/C switch and all accessory switches should be off.

    6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / All Data / Throttle Idle Position and MAP.

    7. Confirm that the Throttle Idle Position is ON and check the MAP value in the Data List while performing the Active Test.

      Note


      • Do not leave the EGR valve open for 10 seconds or more during the Active Test.

      • Be sure to return the EGR valve to step 0 when the Active Test is completed.

      • Do not open the EGR valve 30 steps or more during the Active Test.

      OK
      MAP change in response to EGR step position when Throttle Idle Position is ON in Data List.
      Standard
      - EGR Step Position (Active Test)
      0 Steps 0 to 30 Steps

      MAP

      (Data List)

      		 (EGR valve is fully closed) MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

      Tech Tips


      • While performing the Active Test, if the increase in the value of MAP is small, the EGR valve assembly may be a malfunctioning.

      • Even if the EGR valve assembly is malfunctioning, rough idling or an increase in the value of MAP may occur while performing the Active Test. However, the amount that the value of MAP increases will be smaller than normal.

      Result
      Result Proceed to
      Outside of standard range A
      Within standard range B

    B

    CHECK HARNESS AND CONNECTOR Click here

    A

  17. INSPECT EGR VALVE ASSEMBLY


    1. Remove the EGR valve assembly Click here.

    2. Check if the EGR valve is stuck open.

      OK
      EGR valve is tightly closed.

    3. Reinstall the EGR valve assembly Click here.


    NG

    REPLACE EGR VALVE ASSEMBLY Click here

    OK

  18. CHECK HARNESS AND CONNECTOR


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

      Tech Tips

      Repair any problems.


    NEXT

  19. CHECK WHETHER DTC OUTPUT RECURS


    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. Turn the power switch off.

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

    7. Put the engine in inspection mode Click here.

    8. Start the engine and warm it up.

    9. With the engine warmed up, idle the engine for 2 minutes or more.

    10. Drive the vehicle at between 75 and 120 km/h (45 and 75 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes or more.

      CAUTION:

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

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

    12. Check the pending DTCs.

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

    B

    END

    A

  20. 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 (Check for Open)
      Tester Connection Condition Specified Condition
      B2-5 (VG) - B31-94 (VG) Always Below 1 Ω
      B2-4 (E2G) - B31-117 (E2G) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      B2-5 (VG) or B31-94 (VG) - Body ground Always 10 kΩ or higher

    4. Reconnect the ECM connector.

    5. Reconnect the mass air flow meter sub-assembly connector.


    NG

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

    OK

  21. 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

  22. 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. Turn the power switch off.

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

    7. Put the engine in inspection mode Click here.

    8. Start the engine and warm it up.

    9. With the engine warmed up, idle the engine for 2 minutes or more.

    10. Drive the vehicle at between 75 and 120 km/h (45 and 75 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes or more.

      CAUTION:

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

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

    12. Check 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