SFI SYSTEM, Diagnostic DTC:P0171 and P0172

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

DESCRIPTION

The fuel trim relates to the feedback compensation value, not to the basic injection time. The fuel trim includes the short-term fuel trim and the long-term fuel trim.

The short-term fuel trim is the short-term fuel compensation used to maintain the air fuel ratio at its ideal theoretical value. The signal from the heated oxygen sensor indicates whether the air fuel ratio is rich or lean compared to the ideal theoretical value, triggering a reduction in the fuel volume if the air fuel ratio is rich, and an increase in the fuel 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.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

MIL

Memory

P0171

System Too Lean (Bank 1)

When air fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on lean side (3 trip detection logic).

  • Fuel injector assembly blockage

  • Manifold absolute pressure sensor

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leak from exhaust system

  • Open or short in heated oxygen sensor (sensor 1) circuit

  • Heated oxygen sensor (sensor 1)

  • ECM

Come on

DTC stored (Euro-OBD)

- (except Euro-OBD)

P0172

System Too Rich (Bank 1)

When air fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on rich side (3 trip detection logic).

  • Fuel injector assembly blockage

  • Manifold absolute pressure sensor

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leak from exhaust system

  • Open or short in heated oxygen sensor (sensor 1) circuit

  • Heated oxygen sensor (sensor 1)

  • ECM

Come on

DTC stored

- (except Euro-OBD)
Tip:

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

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

  • If the total of the short-term fuel trim value and long-term fuel trim value is within 20%, the system functions normally.

  • When the air fuel learning value is 1.31 or more, DTC P0171 is stored.

  • When the air fuel learning value is 0.77 or less, DTC P0172 is stored.

WIRING DIAGRAM

Refer to DTC P0130.

Click here

CONFIRMATION DRIVING PATTERN

CAUTION:

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

These DTCs are detected when the vehicle is driven for approximately 20 minutes at a constant vehicle speed of between 80 and 100 km/h (50 and 62 mph) with the shift lever in the 5th position (a malfunction is detected if the learning value of the driving range deviates by 25%).

CAUTION / NOTICE / HINT

Note:

After replacing the ECM, perform idle learning.

Click here

Tip:

  • 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 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.

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.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      DTC P0171 or P0172 is output

      A

      DTC P0171 or P0172 and other DTCs are output

      B
      Tip:

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

    B

    GO TO DTC CHART

    Click here

    A

  2. 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 3 minutes.

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

      Powertrain > Engine and ECT > Active Test

      Active Test Display

      Control the Injection Volume for A/F Sensor

      Data List Display

      O2S B1S1

      O2S B1S2

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

    7. Monitor the voltage output of the heated oxygen sensor (sensor 1) and heated oxygen sensor (sensor 2) (O2S B1S1 and O2S B1S2) displayed on the GTS.

      Tip:

      • 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 heated oxygen sensor (sensor 1) has an output delay of a few seconds and the heated oxygen sensor (sensor 2) 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.

      Result

      The heated oxygen sensors reacts in accordance with increases and decreases of the fuel injection volume:

      +12.5% = Rich output

      Higher than 0.55 V

      -12.5% = Lean output

      Below 0.4 V

      A318963E03

      The following procedure enables the technician to check and graph the voltage outputs of both the 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 / O2S B1S1 and O2S B1S2; then press the view button.

      Tip:

      If the vehicle is short of fuel, the air fuel ratio becomes lean and the heated oxygen sensor DTCs are recorded, and then the MIL illuminates.

      Result

      Result

      Proceed to

      Case 3

      A

      Case 2

      B

      Case 1

      C
    B

    CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR (SENSOR 1) - ECM)Click here

    C

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

    A

  3. 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 / All Data / Coolant Temp.

      Powertrain > Engine and ECT > Data List

      Tester Display

      Coolant Temp

    5. Read the Data List twice, when the engine is both cold and warmed up.

      Standard

      GTS Display

      Condition

      Specified Condition

      Coolant Temp

      Cold engine

      Same as ambient air temperature

      Warm engine

      Between 75 and 100°C (167 and 212°F)

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR

    Click here

    OK

  4. READ VALUE USING GTS (MAP)

    1. Connect the GTS to the DLC3.

    2. Start the engine.

    3. Turn the GTS on.

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

      Powertrain > Engine and ECT > Data List

      Tester Display

      Engine Speed

      MAP

      Coolant Temp

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

    6. Read the MAP value at idling and 2500 rpm.

      Standard Value

      Condition

      Specified Condition

      Ignition switch ON (Engine not running)

      80 to 110 kPa

      Idling (Shift lever in neutral position and A/C off)

      29 to 37 kPa

      2500 rpm (Shift lever in neutral position and A/C off)

      22 to 50 kPa

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE MANIFOLD ABSOLUTE PRESSURE SENSOR

    Click here

    OK

  5. CHECK FOR SPARK (SPARK TEST)

    1. Perform a spark test.

      Click here

      Tip:

      • 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 GTS. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #3 Misfire Count).

    Result

    Proceed to

    NEXT
    NEXT

  6. CHECK FOR EXHAUST GAS LEAK

    1. Check the exhaust gas leaks.

      OK

      No gas leaks.

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  7. CHECK FUEL PRESSURE

    1. Check the fuel pressure.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

    1. Check the injection and volume.

      Tip:

      • Refer to the fuel injector assembly inspection procedure.

        Click here

      • If the fuel injector assemblies malfunction, engine misfire may occur. The misfire count can be read using the GTS. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #3 Misfire Count).

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE FUEL INJECTOR ASSEMBLY

    Click here

    OK

  9. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR (SENSOR 1) - ECM)

    1. Disconnect the heated oxygen sensor (sensor 1) 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

      B4-4 (OX1A) - B31-102 (OX1A)

      Always

      Below 1 Ω

      B4-2 (HT1A) - B31-24 (HT1A)

      Always

      Below 1 Ω

      B4-3 (E1) - B31-101 (E11)

      Always

      Below 1 Ω

      B4-4 (OX1A) or B31-102 (OX1A) - Body ground

      Always

      10 kΩ or higher

      B4-2 (HT1A) or B31-24 (HT1A) - Body ground

      Always

      10 kΩ or higher

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  10. REPLACE HEATED OXYGEN SENSOR (SENSOR 1)

    1. Replace the heated oxygen sensor (sensor 1).

      Click here

    Result

    Proceed to

    NEXT
    NEXT

  11. 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.

      Powertrain > Engine and ECT > Clear DTCs

    5. Turn the ignition switch off and wait for at least 30 seconds.

    6. Start the engine and warm it up.

    7. Turn the GTS on.

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

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

    10. Read the pending DTCs.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      DTCs are not output

      A

      DTC P0171 or P0172 is output

      B
    A

    END

    B

    REPLACE ECM

    Click here