SFI SYSTEM, Diagnostic DTC:P0171,P0172,P2177 and P2178

DTC Code DTC Name
P0171 System Too Lean Bank 1
P0172 System Too Rich Bank 1
P2177 System Too Lean Off Idle Bank 1
P2178 System Too Rich Off Idle 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 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 heated oxygen sensor (sensor 1) 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 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

Fuel trim is considerably in error to lean side.

  • Intake system

  • Fuel injector assembly

  • Air pressure sensor assembly

  • Engine coolant temperature sensor

  • Fuel pressure

  • Fuel system

  • Gas leak from exhaust system

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

  • Heated oxygen sensor (sensor 1)

  • Open or short in heated oxygen sensor (sensor 2) circuit

  • Heated oxygen sensor (sensor 2)

  • Engine mechanical system

  • Emission control system

  • Wire harness or connector

  • ECM

Comes on

DTC stored

P0172

System Too Rich Bank 1

Fuel trim is considerably in error to rich side.

  • Intake system

  • Fuel injector assembly

  • Air pressure sensor assembly

  • Engine coolant temperature sensor

  • Fuel pressure

  • Fuel system

  • Gas leak from exhaust system

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

  • Heated oxygen sensor (sensor 1)

  • Open or short in heated oxygen sensor (sensor 2) circuit

  • Heated oxygen sensor (sensor 2)

  • Engine mechanical system

  • Emission control system

  • Wire harness or connector

  • ECM

Comes on

DTC stored

P2177

System Too Lean Off Idle Bank 1

Stuck on lean side.

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

  • Heated oxygen sensor (sensor 1)

  • Open or short in heated oxygen sensor (sensor 2) circuit

  • Heated oxygen sensor (sensor 2)

Comes on

DTC stored

P2178

System Too Rich Off Idle Bank 1

Stuck on rich side.

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

  • Heated oxygen sensor (sensor 1)

  • Open or short in heated oxygen sensor (sensor 2) circuit

  • Heated oxygen sensor (sensor 2)

Comes on

DTC stored

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.

WIRING DIAGRAM

Refer to DTC P0031 for the heated oxygen sensor circuit.

Click here

CAUTION / NOTICE / HINT

Tip:

  • 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, P0172, P2177 OR P2178)

    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 / Trouble Codes.

    5. Check for DTCs.

      Powertrain > Engine > Trouble Codes

      Result

      Result

      Proceed to

      DTC P0171, P0172, P2177 and/or P2178 are output

      A

      DTC P0171, P0172, P2177 and/or P2178 and other DTCs are output

      B
      Tip:

      If any DTCs other than P0171, P0172, P2177 or P2178 are output, troubleshoot those DTCs first.

    B

    GO TO DTC CHART

    Click here

    A

  2. CHECK INTAKE SYSTEM

    1. Check the intake system for vacuum leaks.

      Click here

      OK

      No leaks in intake system.

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE INTAKE SYSTEM

    OK

  3. INSPECT ENGINE COOLANT TEMPERATURE SENSOR

    1. Inspect the engine coolant temperature sensor.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR

    Click here

    OK

  4. 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 GAS LEAK POINT

    OK

  5. CHECK IGNITION SYSTEM

    1. Check the ignition system.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  6. INSPECT FUEL INJECTOR ASSEMBLY

    1. Inspect the fuel injector assembly.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE FUEL INJECTOR ASSEMBLY

    Click here

    OK

  7. CHECK ENGINE MECHANICAL SYSTEM

    1. Check for mechanical malfunctions that affect the valve timing, such as a jumped tooth or stretching of the timing belt.

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE ENGINE MECHANICAL SYSTEM

    OK

  8. CHECK EMISSION CONTROL SYSTEM

    1. Check the emission control system.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE EMISSION CONTROL SYSTEM

    OK

  9. CHECK FUEL SYSTEM

    1. Check the fuel system.

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  10. READ VALUE USING GTS (MEASURING OF THE INLET PRESSURE)

    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 / Data List / Measuring of the Inlet Pressure.

      Powertrain > Engine > Data List

      Tester Display

      Measuring of the Inlet Pressure

    5. Read the value while ignition switch to ON and engine running.

      Standard

      Data List

      Condition

      Value

      Measuring of the Inlet Pressure

      Ignition switch ON

      Same value as the actual atmospheric pressure

      Idling with warm engine

      20 to 40 kPa
    Tip:

    • Standard atmospheric pressure is 101 kPa(abs) [758 mmHg(abs)]. For every 100 m (328 ft.) increase in altitude, atmospheric pressure drops by approximately 1 kPa (7.5 mmHg). The pressure also varies due to the weather (high atmospheric pressure, low atmospheric pressure).

    • Check "Atmospheric Pressure" in the Data List.

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE AIR PRESSURE SENSOR ASSEMBLY

    Click here

    OK

  11. READ VALUE USING GTS (UPSTREAM PROBE O2 VOLTAGE)

    1. Connect the GTS to the DLC3.

    2. Start the engine and warm it up.

    3. Turn the GTS on.

    4. Enter the following menus: Powertrain / Engine / Data List / Engine Regime and Upstream Probe O2 Voltage.

      Powertrain > Engine > Data List

      Tester Display

      Engine Regime

      Upstream Probe 02 Voltage

    5. According to the display on the GTS, read the Data List item Upstream Probe O2 Voltage while maintaining the engine speed at 2000 rpm (without load) for 120 seconds.

      OK

      The value alternates between the minimum (0 to 350 mV) and maximum (600 to 1000 mV).

    Result

    Proceed to

    OK

    NG
    NG

    INSPECT HEATED OXYGEN SENSOR (SENSOR 1)Click here

    OK

  12. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P2177 OR P2178)

    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 > Clear DTCs

    5. Turn the ignition switch off and wait for a few minutes.

    6. Perform the drive test.

    7. Turn the GTS on.

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

    9. Check for DTCs.

      Powertrain > Engine > Trouble Codes

    Result

    Result

    Proceed to

    DTC P0171, P0172, P2177 or P2178 is output

    A

    DTCs are not output

    B
    A

    REPLACE ECM

    Click here

    B

    CHECK FOR INTERMITTENT PROBLEMS

    Click here

  13. INSPECT HEATED OXYGEN SENSOR (SENSOR 1)

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

      Click here

    Result

    Proceed to

    OK

    NG
    NG

    REPLACE HEATED OXYGEN SENSOR (SENSOR 1)

    Click here

    OK

  14. 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

      B35-2 (HT1A) - B55-3 (HT1A)

      Always

      Below 1 Ω

      B35-3 (EX1A) - B55-20 (EX1A)

      Always

      Below 1 Ω

      B35-4 (OX1A) - B55-8 (OX1A)

      Always

      Below 1 Ω

      B35-2 (HT1A) or B55-3 (HT1A) - Body ground and other terminals

      Always

      10 kΩ or higher

      B35-3 (EX1A) or B55-20 (EX1A) - Body ground and other terminals

      Always

      10 kΩ or higher

      B35-4 (OX1A) or B55-8 (OX1A) - Body ground and other terminals

      Always

      10 kΩ or higher

    Result

    Proceed to

    OK

    NG
    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  15. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P2177 OR P2178)

    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 > Clear DTCs

    5. Turn the ignition switch off and wait for a few minutes.

    6. Perform the drive test.

    7. Turn the GTS on.

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

    9. Check for DTCs.

      Powertrain > Engine > Trouble Codes

    Result

    Result

    Proceed to

    DTC P0171, P0172, P2177 or P2178 is output

    A

    DTCs are not output

    B
    A

    REPLACE ECM

    Click here

    B

    CHECK FOR INTERMITTENT PROBLEMS

    Click here