SFI SYSTEM(w/o EGR System), Diagnostic DTC:P0171,P0172,P0174 and P0175

DTC Code DTC Name
P0171 System Too Lean (Bank 1)
P0172 System Too Rich (Bank 1)
P0174 System Too Lean (Bank 2)
P0175 System Too Rich (Bank 2)

DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection time. 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 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.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

Warning Indicate

Memory

P0171

System Too Lean (Bank 1)

With a warm engine and stable air-fuel ratio feedback, the fuel trim is considerably in error to the lean side (2 trip detection logic).

  • Air induction system

  • Fuel injector blockage

  • Mass air flow meter assembly

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leak from exhaust system

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

  • Air fuel ratio sensor (for Sensor 1)

  • Air fuel ratio sensor heater (for Sensor 1)

  • No. 1 integration relay

  • Air fuel ratio sensor heater and No. 1 integration relay circuits

  • PCV valve and hose

  • PCV hose connections

  • ECM

  • Wire harness or connector

Comes on

DTC stored

P0172

System Too Rich (Bank 1)

With a warm engine and stable air-fuel ratio feedback, the fuel trim is considerably in error to the rich side (2 trip detection logic).

  • Fuel injector leak or blockage

  • Mass air flow meter assembly

  • Engine coolant temperature sensor

  • Ignition system

  • Fuel pressure

  • Gas leak from exhaust system

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

  • Air fuel ratio sensor (for Sensor 1)

  • Air fuel ratio sensor heater (for Sensor 1)

  • No. 1 integration relay

  • Air fuel ratio sensor heater and No. 1 integration relay circuits

  • ECM

Comes on

DTC stored

P0174

System Too Lean (Bank 2)

With a warm engine and stable air-fuel ratio feedback, the fuel trim is considerably in error to the lean side (2 trip detection logic).

  • Air induction system

  • Fuel injector blockage

  • Mass air flow meter assembly

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leak from exhaust system

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

  • Air fuel ratio sensor (for Sensor 1)

  • Air fuel ratio sensor heater (for Sensor 1)

  • No. 1 integration relay

  • Air fuel ratio sensor heater and No. 1 integration relay circuits

  • PCV valve and hose

  • PCV hose connections

  • ECM

  • Wire harness or connector

Comes on

DTC stored

P0175

System Too Rich (Bank 2)

With a warm engine and stable air-fuel ratio feedback, the fuel trim is considerably in error to the rich side (2 trip detection logic).

  • Fuel injector leak or blockage

  • Mass air flow meter assembly

  • Engine coolant temperature sensor

  • Ignition system

  • Fuel pressure

  • Gas leak from exhaust system

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

  • Air fuel ratio sensor (for Sensor 1)

  • Air fuel ratio sensor heater (for Sensor 1)

  • No. 1 integration relay

  • Air fuel ratio sensor heater and No. 1 integration relay circuits

  • ECM

Comes on

DTC stored

Tip:
  • When DTC P0171 or P0174 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 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 or P0174 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 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.

A121607E01

CONFIRMATION DRIVING PATTERN

A199233E36
  1. Connect the intelligent tester to the DLC3.

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

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

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

  5. Turn the engine switch on (IG) and turn the tester 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 (38 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 / DTC [E].

  10. Read the pending DTCs.

    Tip:

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

WIRING DIAGRAM

Refer to DTC P2195 (Click here).

CAUTION / NOTICE / HINT

Tip:
  • Read freeze frame data using the intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. 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.

  • Bank 1 refers to the bank that includes the No. 1 cylinder*.

    *: The No. 1 cylinder is the cylinder which is farthest from the transmission.

  • Bank 2 refers to the bank that does not include the No. 1 cylinder.

  • 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 FOR ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175)

    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

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

    5. Read DTCs.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      P0171, P0172, P0174 or P0175 is output

      A

      P0171, P0172, P0174 or P0175 and other DTCs are output

      B

      Tip:

      If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.

    B

    GO TO DTC CHART

    A
  2. CHECK PCV HOSE CONNECTIONS

    1. Check the PCV hose connections.

      Click here

      OK

      PCV hose is connected correctly and is not damaged.

      Result

      Result

      OK

      NG

    NG

    REPAIR OR REPLACE PCV HOSE

    OK
  3. CHECK AIR INDUCTION SYSTEM

    1. Check the air induction system for vacuum leaks.

      Click here

      OK

      No leaks in air induction system.

      Result

      Result

      OK

      NG

    NG

    REPAIR OR REPLACE AIR INDUCTION SYSTEM

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

    1. Connect the intelligent tester to the DLC3.

    2. Start the engine.

    3. Turn the tester on.

    4. Warm up the engine and run 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.

      Powertrain > Engine and ECT > Active Test

      Tester Display

      Control the Injection Volume

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

    7. Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the tester.

      Tip:
      • 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.

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

      Tester Display (Sensor)

      Injection Volume

      Status

      Voltage

      AFS Voltage B1S1 or AFS Voltage B2S1

      (Air fuel ratio)

      +12%

      Rich

      Below 3.1 V

      AFS Voltage B1S1 or AFS Voltage B2S1

      (Air fuel ratio)

      -12%

      Lean

      Higher than 3.4 V

      O2S B1S2 or O2S B2S2

      (Heated oxygen)

      +12%

      Rich

      Higher than 0.55 V

      O2S B1S2 or O2S B2S2

      (Heated oxygen)

      -12%

      Lean

      Below 0.4 V

      Result

      Status of AFS Voltage B1S1 or AFS Voltage B2S1

      Status of O2S B1S2 or O2S B2S2

      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 assembly

      • Engine coolant temperature sensor

      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 assembly

      • 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 Active Test, the air fuel ratio sensor output voltage (AFS Voltage) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.

      Rich: During the Control the Injection Volume Active Test, the AFS Voltage is consistently below 3.1 V, and the O2S is consistently higher than 0.55 V.

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

      Tip:

      Refer to "Data List / Active Test" [AFS Voltage B1S1, AFS Voltage B2S1, O2S B1S2 and O2S B2S2]

      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 engine switch on (IG).

    3. Turn the tester 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 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).

      Result

      Result

      OK

      NG

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR

    OK
  6. READ VALUE USING INTELLIGENT TESTER (MAF)

    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

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

      Powertrain > Engine and ECT > Data List

      Tester Display

      MAF

      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 18.3 g/sec. and 25.8 g/sec. (shift lever: N; A/C: Off).

      Result

      Result

      OK

      NG

    NG

    CHECK HARNESS AND CONNECTORClick here

    OK
  7. CHECK FUEL PRESSURE

    1. Check the fuel pressure.

      Click here

      Result

      Result

      OK

      NG

    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK
  8. CHECK FOR EXHAUST GAS LEAK

    1. Check for exhaust gas leaks.

      OK

      No gas leaks.

      Result

      Result

      OK

      NG

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK
  9. CHECK FOR SPARKS AND IGNITION

    1. Perform a spark test.

      Click here

      CAUTION:

      Always disconnect all the injector connectors.

      Note:

      Do not crank the engine for more than 2 seconds.

      OK

      Spark jumps across electrode gap.

      Result

      Result

      OK

      NG

    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

      OK

      NG

    OK

    PERFORM CONFIRMATION DRIVING PATTERNClick here

    NG

    REPLACE FUEL INJECTOR ASSEMBLY

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

    1. Inspect the air fuel ratio sensor.

      Click here

      Result

      Result

      OK

      NG

    NG

    REPLACE AIR FUEL RATIO SENSOR

    OK
  12. CHECK TERMINAL VOLTAGE (+B OF AIR FUEL RATIO SENSOR)

    1. A150242C01

      *A

      Bank 1

      *B

      Bank 2

      *a

      Front view of wire harness connector

      (to Air Fuel Ratio Sensor)

      Disconnect the air fuel ratio sensor connector.

    2. Turn the engine switch on (IG).

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

      Standard Voltage

      Tester Connection

      Switch Condition

      Specified Condition

      C20-2 (+B) - Body ground

      Engine switch on (IG)

      11 to 14 V

      C19-2 (+B) - Body ground

      Engine switch on (IG)

      11 to 14 V

      Result

      Result

      OK

      NG

    NG

    CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 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

      Tester Connection

      Condition

      Specified Condition

      C20-1 (HA1A) - C31-17 (HA1A)

      Always

      Below 1 Ω

      C20-3 (A1A+) - C30-1 (A1A+)

      Always

      Below 1 Ω

      C20-4 (A1A-) - C30-2 (A1A-)

      Always

      Below 1 Ω

      C19-1 (HA2A) - C31-19 (HA2A)

      Always

      Below 1 Ω

      C19-3 (A2A+) - C30-7 (A2A+)

      Always

      Below 1 Ω

      C19-4 (A2A-) - C30-8 (A2A-)

      Always

      Below 1 Ω

      C20-1 (HA1A) or C31-17 (HA1A) - Body ground

      Always

      10 kΩ or higher

      C20-3 (A1A+) or C30-1 (A1A+) - Body ground

      Always

      10 kΩ or higher

      C20-4 (A1A-) or C30-2 (A1A-) - Body ground

      Always

      10 kΩ or higher

      C19-1 (HA2A) or C31-19 (HA2A) - Body ground

      Always

      10 kΩ or higher

      C19-3 (A2A+) or C30-7 (A2A+) - Body ground

      Always

      10 kΩ or higher

      C19-4 (A2A-) or C30-8 (A2A-) - Body ground

      Always

      10 kΩ or higher

      Result

      Result

      OK

      NG

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK
  14. REPLACE AIR FUEL RATIO SENSOR

    1. Replace the air fuel ratio sensor.

      Click here

      Result

      Result

      NEXT

    NEXT
  15. PERFORM CONFIRMATION DRIVING PATTERN

    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

    4. Clear the DTCs.

      Click here

      Powertrain > Engine and ECT > Clear DTCs

    5. Turn the engine switch off.

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

    7. Start the engine and warm it up.

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

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

    10. Read DTCs.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      DTC P0171, P0172, P0174 or P0175 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

      Tip:

      Repair any problems.

      Result

      Result

      NEXT

    NEXT
  17. CHECK WHETHER DTC OUTPUT RECURS

    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

    4. Clear the DTCs.

      Click here

      Powertrain > Engine and ECT > Clear DTCs

    5. Turn the engine switch off.

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

    7. Start the engine and warm it up.

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

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

    10. Read DTCs.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      DTC P0171, P0172, P0174 or P0175 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

      Tester Connection

      Condition

      Specified Condition

      C27-3 (VG) - C29-14 (VG)

      Always

      Below 1 Ω

      C27-2 (E2G) - C29-13 (E2G)

      Always

      Below 1 Ω

      C27-3 (VG) or C29-14 (VG) - Body ground

      Always

      10 kΩ or higher

      Result

      Result

      OK

      NG

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK
  19. REPLACE MASS AIR FLOW METER ASSEMBLY

    1. Replace the mass air flow meter assembly.

      Click here

      Tip:

      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 assembly.

      Result

      Result

      NEXT

    NEXT
  20. CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester on.

    4. Clear the DTCs.

      Click here

      Powertrain > Engine and ECT > Clear DTCs

    5. Turn the engine switch off.

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

    7. Start the engine and warm it up.

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

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

    10. Read DTCs.

      Powertrain > Engine and ECT > Trouble Codes

      Result

      Result

      Proceed to

      DTC is not output

      A

      DTC P0171, P0172, P0174 or P0175 is output

      B

    A

    END

    B

    REPLACE ECM

  21. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 INTEGRATION RELAY)

    1. Disconnect the air fuel ratio sensor connector.

    2. Remove the No. 1 integration relay from the engine room relay block.

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

      Standard Resistance

      Tester Connection

      Condition

      Specified Condition

      C20-2 (+B) - 1B-8

      Always

      Below 1 Ω

      C19-2 (+B) - 1B-8

      Always

      Below 1 Ω

      1B-7 - Body ground

      Always

      Below 1 Ω

      C20-2 (+B) or 1B-8 - Body ground

      Always

      10 kΩ or higher

      C19-2 (+B) or 1B-8 - Body ground

      Always

      10 kΩ or higher

      Result

      Result

      OK

      NG

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK
  22. INSPECT NO. 1 INTEGRATION RELAY (A/F)

    1. Inspect the No. 1 integration relay (A/F).

      Click here

      Result

      Result

      OK

      NG

    OK

    CHECK ECM POWER SOURCE CIRCUIT

    NG

    REPLACE NO. 1 INTEGRATION RELAY