SFI SYSTEM, Diagnostic DTC:P0171, P0172, P0174, 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 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 stores a DTC.

DTC No. DTC Detection Condition Trouble Area

P0171

P0174

 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 assembly blockage

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leakage from exhaust system

  • Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit

  • Air fuel ratio sensor (bank 1, 2 sensor 1)

  • Air fuel ratio sensor heater (bank 1, 2 sensor 1)

  • No. 1 integration relay (A/F)

  • Air fuel ratio sensor heater circuits

  • PCV valve and hose

  • PCV hose connections

  • ECM

P0172

P0175

 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

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Ignition system

  • Fuel pressure

  • Gas leakage from exhaust system

  • Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit

  • Air fuel ratio sensor (bank 1, 2 sensor 1)

  • Air fuel ratio sensor heater (bank 1, 2 sensor 1)

  • No. 1 integration relay (A/F)

  • Air fuel ratio sensor heater circuits

  • ECM

Tech Tips


  • 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 becomes 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'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 thresholds, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example:

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

A00OA09E01

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 air fuel ratio sensor function provided 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. Start the engine and turn the intelligent tester on.

  3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

  4. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

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

  6. Monitor the output voltages of the air fuel ratio sensor and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2, or AFS Voltage B2S1 and O2S B2S2) 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.

Tester Display (Sensor) Injection Volume Status Voltage

AFS Voltage B1S1 or AFS Voltage B2S1

(Air fuel ratio sensor)

 +25% Rich Below 3.1 V

AFS Voltage B1S1 or AFS Voltage B2S1

(Air fuel ratio sensor)

 -12.5% Lean Higher than 3.4 V

O2S B1S2 or O2S B2S2

(Heated oxygen sensor)

 +25% Rich Higher than 0.55 V

O2S B1S2 or O2S B2S2

(Heated oxygen sensor)

 -12.5% Lean Below 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 A00O5STE01 A00O3R3E08 A00O5STE01 A00O30ZE04 -
2 A00O5STE01 A00O5QEE01 A00O5STE01 A00O30ZE04

  • Air fuel ratio sensor

  • Air fuel ratio sensor heater

  • Air fuel ratio sensor circuit
3 A00O5STE01 A00O3R3E08 A00O5STE01 A00O5QEE01

  • Heated oxygen sensor

  • Heated oxygen sensor heater

  • Heated oxygen sensor circuit
4 A00O5STE01 A00O5QEE01 A00O5STE01 A00O5QEE01

  • Fuel injector assembly

  • Fuel pressure

  • Gas leakage from exhaust system (Air fuel ratio extremely rich or lean)

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 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 ignition switch to ON and turn the intelligent tester on.

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

    4. Read the DTCs.

      Result
      Result Proceed to
      P0171, P0172, P0174 or P0175 A
      P0171, P0172, P0174 or P0175 and other DTCs B

      Tech Tips

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


    B

    GO TO DTC CHART Click here

    A

  2. CHECK PCV HOSE CONNECTIONS


    1. Check the PCV hose connections.

      OK
      PCV hose is connected correctly and is not damaged.

    NG

    REPAIR OR REPLACE PCV HOSE

    OK

  3. CHECK AIR INDUCTION SYSTEM


    1. Check the air induction system for vacuum leakage.

      OK
      No leakage in air induction system.

    NG

    REPAIR OR REPLACE AIR INDUCTION SYSTEM

    OK

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


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine and turn the intelligent tester on.

    3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.

    4. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

    5. 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).

    6. Monitor the voltage outputs 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 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.

      Standard

      Tester Display

      (Sensor)

      		 Injection Volume Status Voltage

      AFS Voltage B1S1 or AFS Voltage B2S1

      (Air fuel ratio sensor)

      		 +25% Rich Below 3.1

      AFS Voltage B1S1 or AFS Voltage B2S1

      (Air fuel ratio sensor)

      		 -12.5% Lean Higher than 3.4

      O2S B1S2 or O2S B2S2

      (Heated oxygen sensor)

      		 +25% Rich Higher than 0.55

      O2S B1S2 or O2S B2S2

      (Heated oxygen sensor)

      		 -12.5% Lean Below 0.4
      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 - - C
      Lean Lean Actual air fuel ratio lean May occur

      • PCV valve and hose

      • PCV hose connections

      • Fuel injector assembly blockage

      • Gas leakage from exhaust system

      • Air induction system

      • Fuel pressure

      • Mass air flow meter

      • Engine coolant temperature sensor

      		 A
      Rich Rich Actual air fuel ratio rich -

      • Fuel injector assembly leakage blockage or blockage

      • Gas leakage from exhaust system

      • Ignition system

      • Fuel pressure

      • Mass air flow meter

      • 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) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.

      Rich: During Control the Injection Volume for A/F Sensor, the AFS is consistently below 3.1 V, and the O2S is consistently higher 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 (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 ignition switch to ON and turn the intelligent tester on.

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

    4. Read the Data List twice, when the engine is cold and when it is warmed up.

      Standard
      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


    1. Inspect the mass air flow meter Click here.


    NG

    REPLACE MASS AIR FLOW METER Click here

    OK

  7. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. CHECK FOR EXHAUST GAS LEAK


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

      OK
      No gas leakage.

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. CHECK SPARK AND IGNITION


    1. Check the ignition system Click here.

      Tech Tips

      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 / All Data / Cylinder #1 Misfire Rate (to Cylinder #6 Misfire Count).


    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)


    1. Inspect the fuel injector assembly Click here.

      Tech Tips

      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 / All Data / Cylinder #1 Misfire Rate (to Cylinder #6 Misfire Count).


    NG

    REPLACE FUEL INJECTOR ASSEMBLY Click here

    OK

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    1. Inspect the air fuel ratio sensor Click here.


    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

  12. INSPECT NO. 1 INTEGRATION RELAY (A/F)


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


    NG

    REPLACE NO. 1 INTEGRATION RELAY (A/F)

    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 (Check for Open)
      Tester Connection Condition Specified Condition
      C25-1 (HA1A) - C37-17 (HA1A) Always Below 1 Ω
      C26-1 (HA2A) - C37-19 (HA2A) Always Below 1 Ω
      Standard Resistance (Check for Short)
      Tester Connection Condition Specified Condition
      C25-1 (HA1A) or C37-17 (HA1A) - Body ground Always 10 kΩ or higher
      C26-1 (HA2A) or C37-19 (HA2A) - 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

    OK

  14. REPLACE AIR FUEL RATIO SENSOR


    1. Replace the air fuel ratio sensor Click here.


    NEXT

  15. PERFORM CONFIRMATION DRIVING PATTERN

    A00O78YE38

    1. Connect the intelligent tester to the DLC3 (step "a").

    2. Turn the ignition switch to ON and turn the intelligent tester on (step "b").

    3. Clear DTCs Click here (step "c").

    4. Switch the ECM from normal mode to check mode using the intelligent tester Click here (step "d").

    5. Start the engine and warm it up with all the accessories switched off (step "e").

    6. Drive the vehicle at between 60 km/h and 120 km/h (38 mph and 75 mph) and at an engine speed of between 1400 rpm and 3200 rpm for 3 to 5 minutes (step "f").

      Tech Tips

      If the system is still malfunctioning, the MIL is illuminated during this step.

      Note

      If the conditions in this test are not strictly followed, no malfunction will be detected.


    NEXT

  16. CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175)


    1. Connect the intelligent tester to the DLC3.

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

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

    4. Read the DTCs.

      Result
      Result Proceed to
      No output A
      P0171, P0172, P0174 or P0175 B

    B

    REPLACE ECM Click here

    A

    END