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 time. The fuel trim consists of both the short-term and the 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 (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 it is lean.

Factors such as individual engine differences, wear over time, and change 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 a warm engine and stable air fuel ratio feedback, the fuel trim is considerably in error to the lean side (2-trip detection logic).

  • Intake system

  • Fuel pressure

  • Injector blockage

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Gas leakage from exhaust system

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

  • Air fuel ratio sensor (sensor 1)

  • Air fuel ratio sensor heater (sensor 1)

  • Air fuel ratio sensor heater circuits

  • PCV hose connections

  • PCV valve and hose

  • ECM
P0172 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).

  • Injector leakage or blockage

  • Fuel pressure

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Ignition system

  • Gas leakage from exhaust system

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

  • Air fuel ratio sensor (sensor 1)

  • Air fuel ratio sensor heater (sensor 1)

  • Air fuel ratio sensor heater circuits

  • Ignition system

  • ECM

Tech Tips


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

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

  • When the total of the short-term and long-term fuel trim values is within 20% of the central value (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's estimated fuel injection volumes 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 threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example:

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

A00OL0IE10

WIRING DIAGRAM

Refer to DTC P2195 Click here.

INSPECTION PROCEDURE

Tech Tips


  • 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.

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 ignition switch to ON.

    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. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (AIR FUEL RATIO CONTROL)


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine.

    3. Turn the tester on.

    4. Warm up 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 for A/F Sensor.

    6. Perform the "Control the Injection Volume for A/F Sensor" operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).

    7. Monitor the output voltages of the air fuel ratio sensor (sensor 1) and heated oxygen sensor (sensor 2) (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.

      Result
      The air fuel ratio sensor (sensor 1) reacts in accordance with increases and decreases in the fuel injection volume:
      +25% = Rich output
      Higher than 3.4 V
      -12.5% = Lean output
      Below 3.1 V

      Note

      The air fuel ratio 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.

      Case

      A/F Sensor (Sensor 1)

      Output Voltage

      HO2 Sensor (Sensor 2)

      Output Voltage

      		 Main Suspected Trouble Area
      1 A00OMXTE11 A00ONS5E11 -
      2 A00OJZJE02 A00ONS5E11

      • Air fuel ratio sensor

      • Air fuel ratio sensor heater

      • Air fuel ratio sensor circuit
      3 A00OJZJE02 A00OJZJE02

      • Fuel pressure

      • Gas leakage from exhaust system

        (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 sensor (sensor 1) and heated oxygen sensor (sensor 2).

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

      Result
      Result Proceed to
      Case 1 A
      Case 2 B
      Case 3 C

    B

    INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here

    C

    CHECK FOR EXHAUST GAS LEAK Click here

    A

  3. CONFIRM IF VEHICLE HAS RUN OUT OF FUEL IN PAST


    1. Has the vehicle run out of fuel in the past?


    NO

    CHECK FOR EXHAUST GAS LEAK Click here

    YES

  4. PERFORM CONFIRMATION DRIVING PATTERN

    A00OJBPE04

    1. Connect the intelligent tester to the DLC3 (Procedure "A").

    2. Turn the ignition switch to ON (Procedure "B").

    3. Turn the tester on (Procedure "C").

    4. Clear the DTCs Click here (Procedure "D").

    5. Switch the ECM from normal mode to check mode Click here (Procedure "E").

    6. Start the engine (Procedure "F").

    7. Allow the engine to idle until the engine coolant temperature reaches 40°C (104°F) (Procedure "G").

    8. Drive the vehicle at a vehicle speed of more than 40 km/h (25 mph) for 35 seconds or more (Procedure "H").

    9. Allow the engine to idle for 40 seconds or more (Procedure "I").

    10. Repeat procedures "G" and "I" described above at least 3 times (Procedure "J").

    11. Allow the engine to idle for 40 seconds or more (Procedure "K").

      Tech Tips

      The MIL is illuminated during procedure "K" if a malfunction still exists.

      Note

      If the conditions in this test are not strictly followed, malfunctions may not be detected.


    NEXT

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    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 is not output B

    B

    SYSTEM IS OK

    A

  6. CHECK FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leakage.

      OK
      No gas leakage.

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  7. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG

    CHECK FUEL LINE Click here

    OK

  8. INSPECT INJECTOR ASSEMBLY (INJECTION VOLUME)


    1. Check the injection volume Click here.


    NG

    REPLACE FUEL INJECTOR ASSEMBLY Click here

    OK

  9. INSPECT MASS AIR FLOW METER


    1. Inspect the mass air flow meter Click here.


    NG

    REPLACE MASS AIR FLOW METER Click here

    OK

  10. READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON and turn the tester on.

    3. Enter the following menus: Powertrain / Engine and ECT / Data List / Primary / Coolant Temp.

    4. Read the 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).

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

    OK

  11. 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

  12. CHECK INTAKE SYSTEM


    1. Check the intake system for vacuum leakage Click here.

      OK
      No leakage from intake system.

    NG

    REPAIR OR REPLACE INTAKE SYSTEM

    OK

  13. CHECK IGNITION SYSTEM


    1. Inspect the ignition system Click here.


    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  14. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. A00OJ5OE28
      Text in Illustration
      *1

      Component without harness connected

      (Air Fuel Ratio Sensor)

      Disconnect the air fuel ratio sensor connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      1 (HA1A) - 2 (+B) 20°C (68°F) 1.8 to 3.4 Ω
      1 (HA1A) - 4 (A1A-) Always 10 kΩ or higher

    3. Reconnect the air fuel ratio sensor connector.


    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

  15. CHECK AIR FUEL RATIO SENSOR (POWER SOURCE)


    1. A00OKBPE01
      Text in Illustration
      *1

      Front view of wire harness connector

      (to Air Fuel Ratio Sensor)

      Disconnect the air fuel ratio sensor connector.

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      B18-2 (+B) - Body ground Ignition switch ON 11 to 14 V

    3. Reconnect the air fuel ratio sensor connector.


    NG

    CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY [EFI MAIN RELAY]) Click here

    OK

  16. 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
      B18-1 (HA1A) - B39-104 (HA1A) Always Below 1 Ω
      B18-3 (A1A+) - B39-103 (A1A+) Always Below 1 Ω
      B18-4 (A1A-) - B39-126 (A1A-) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      B18-1 (HA1A) or B39-104 (HA1A) - Body ground Always 10 kΩ or higher
      B18-3 (A1A+) or B39-103 (A1A+) - Body ground Always 10 kΩ or higher
      B18-4 (A1A-) or B39-126 (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

  17. REPLACE AIR FUEL RATIO SENSOR


    1. Replace the air fuel ratio sensor Click here.


    NEXT

  18. PERFORM CONFIRMATION DRIVING PATTERN

    A00OJBPE04

    1. Connect the intelligent tester to the DLC3 (Procedure "A").

    2. Turn the ignition switch to ON (Procedure "B").

    3. Turn the tester on (Procedure "C").

    4. Clear the DTCs Click here (Procedure "D").

    5. Switch the ECM from normal mode to check mode Click here (Procedure "E").

    6. Start the engine (Procedure "F").

    7. Allow the engine to idle until the engine coolant temperature reaches 40°C (104°F) (Procedure "G").

    8. Drive the vehicle at a vehicle speed of more than 40 km/h (25 mph) for 35 seconds or more (Procedure "H").

    9. Allow the engine to idle for 40 seconds or more (Procedure "I").

    10. Repeat procedure "G" and "I" described above at least 3 times (Procedure "J").

    11. Allow the engine to idle for 40 seconds or more (Procedure "K").

      Tech Tips

      The MIL is illuminated during procedure "K" if a malfunction still exists.

      Note

      If the conditions in this test are not strictly followed, malfunctions may not be detected.


    NEXT

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


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the tester on.

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

    5. Read the DTCs.

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

    B

    REPLACE ECM Click here

    A

    END

  20. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY [EFI MAIN RELAY])


    1. A00OJZVE01
      Text in Illustration
      *1

      Front view of wire harness connector

      (to Air Fuel Ratio Sensor)
      *2 Engine Room No. 1 Relay Block
      *3

      Front view of wire harness connector

      (to Integration Relay)

      Disconnect the air fuel ratio sensor connector.

    2. Remove the integration relay (EFI MAIN relay) from the engine room No. 1 relay block.

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

      Standard Resistance (Check for Open)
      Tester Connection Condition Specified Condition
      B18-2 (+B) - 1B-4 Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      B18-2 (+B) or 1B-4 - Body ground Always 10 kΩ or higher

    4. Reconnect the air fuel ratio sensor connector.

    5. Reinstall the integration relay.


    NG

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

    OK

    CHECK ECM POWER SOURCE CIRCUIT Click here

  21. CHECK FUEL LINE


    1. Check the fuel lines for leaks or blockage Click here.

      OK
      No leaks or blockage.

    NG

    REPAIR OR REPLACE FUEL LINE

    OK

    REPLACE FUEL PUMP Click here