SFI SYSTEM (w/ EGR 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
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

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, a fuel injection volume that deviates from that estimated by the ECM causes 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 value. Deviations from the ECM's estimated fuel injection volume 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 a malfunction threshold, the ECM interprets this a fault in the fuel system and sets a DTC.

Example:

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

A01J8S1E32

WIRING DIAGRAM

Refer to DTC P2195 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.

  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 A01J9MUE12 A01J9GBE12 -
    2 A01JD4VE06 A01J9GBE12

    • Air fuel ratio sensor

    • Air fuel ratio sensor heater

    • Air fuel ratio sensor circuit
    3 A01J9MUE12 A01JD4VE07

    • Heated oxygen sensor

    • Heated oxygen sensor heater

    • Heated oxygen sensor circuit

    • Exhaust gas leaks
    4 A01JD4VE06 A01JD4VE06

    • 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 / A/F Control System / AFS Voltage B1S1 and O2S B1S2.

      Note

      Inspect the fuses for circuits related to this system before performing the following inspection procedure.

      Tech Tips


      • 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.

      • 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 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. Inspect 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 (AIR FUEL RATIO CONTROL)


    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.

    7. 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).

    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


      • 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.

      • 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)

      		 +25% Rich Less than 3.1 V
      -12.5% Lean More than 3.4 V

      O2S B1S2

      (heated oxygen)

      		 +25% Rich More than 0.55 V
      -12.5% 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 - - C
      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

      • Engine coolant temperature sensor

      		 A
      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

      • 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 Control the Injection Volume for A/F Sensor, 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 for A/F Sensor, 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 for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor alternates correctly.


    B

    INSPECT AIR FUEL RATIO SENSOR NO.2 (HEATER RESISTANCE) Click here

    C

    PERFORM CONFIRMATION DRIVING PATTERN 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 / Coolant Temp.

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

      Standard value
      With cold engine: Same as ambient air temperature.
      With warm engine: 80 to 100°C (176 to 212°F).

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

    OK

  6. INSPECT MASS AIR FLOW METER SUB-ASSEMBLY


    1. Inspect the mass air flow meter sub-assembly Click here.


    NG

    REPLACE MASS AIR FLOW METER SUB-ASSEMBLY Click here

    OK

  7. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. INSPECT FOR EXHAUST GAS LEAK


    1. Inspect for exhaust gas leaks from the exhaust manifold sub-assembly and exhaust pipes.

      OK
      No gas leaks.

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. CHECK SPARK AND IGNITION

    Tech Tips


    • Refer to the ignition system inspection procedure Click here.

    • If the spark plugs or ignition system malfunctions, engine misfires may occur. The misfire count can be read using the intelligent tester. Enter the following menus: Powertrain / Engine and ECT / Data List / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count)


    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

    Tech Tips


    • Refer to the fuel injector inspection procedure Click here.

    • If the injectors malfunction, engine misfires may occur. The misfire count can be read using the intelligent tester. Enter the following menus: Powertrain / Engine and ECT / Data List / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).

    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 NO.2 (HEATER RESISTANCE)


    1. A01JBE1E11
      Text in Illustration
      *1

      Component without harness connected

      (to 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 NO.2 Click here

    OK

  12. CHECK TERMINAL VOLTAGE (POWER SOURCE OF AIR FUEL RATIO SENSOR)


    1. A01JCK7E01
      Text in Illustration
      *1

      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
      D24-2 (+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 - EFI MAIN RELAY)

    OK

  13. CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)


    1. Disconnect the air fuel ratio sensor connector.

      A01JC98E02

    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
      D24-1 (HA1A) - D28-18 (HA1A) Always Below 1 Ω
      D24-3 (A1A+) - D28-103 (A1A+) Always Below 1 Ω
      D24-4 (A1A-) - D28-126 (A1A-) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      D24-1 (HA1A) or D28-18 (HA1A) - Body ground Always 10 kΩ or higher
      D24-3 (A1A+) or D28-103 (A1A+) - Body ground Always 10 kΩ or higher
      D24-4 (A1A-) or D28-126 (A1A-) - Body ground Always 10 kΩ or higher
      Text in Illustration
      *1

      Front view of wire harness connector

      (to Air Fuel Ratio Sensor)

      		 *2

      Front view of wire harness connector

      (to ECM)

    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 NO.2


    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 and wait for 30 seconds.

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

    7. Put the engine in inspection mode Click here.

    8. Start the power 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.

    11. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

    12. Input the DTC: P0171, P0172.

    13. Check the DTC judgment result.

      Result
      Result Proceed to
      ABNORMAL (DTC P0171 or P0172 is output) A
      NORMAL (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

    REPLACE ECM 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. REPLACE ECM


    1. Replace the ECM Click here.


    NEXT

  19. 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 DTC Click here.

    5. Turn the power switch off and wait for 30 seconds.

    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.

    11. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.

    12. Input the DTCs: P0171, P0172.

    13. Check the DTCs judgment result.


    NEXT

    END