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 the 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 (A/F) 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 Code 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

  • Injector blockage

  • Mass Air Flow (MAF) meter

  • Engine Coolant Temperature (ECT) sensor

  • Fuel pressure

  • Gas leakage from exhaust system

  • Open or short in Air Fuel ratio (A/F) sensor (for Sensor 1) circuit

  • A/F sensor (for Sensor 1)

  • A/F sensor heater (for Sensor 1)

  • Integration relay

  • A/F sensor heater and integration relay 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

  • MAF meter

  • ECT sensor

  • Ignition system

  • Fuel pressure

  • Gas leakage from exhaust system

  • Open or short in A/F sensor (for Sensor 1) circuit

  • A/F sensor (for Sensor 1)

  • A/F sensor heater (for Sensor 1)

  • Integration relay

  • A/F sensor heater and integration relay 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 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 DTC(s).

Example:

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

A01ER45E01

WIRING DIAGRAM

Refer to DTC P2195 Click here.

INSPECTION PROCEDURE

Tech Tips


  • DTC P0171, P0172, P0174 and P0175 are for Euro-OBD only.

  • 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 A/F sensor voltage could be caused by a rich air-fuel mixture. Check for conditions that would cause the engine to run rich.

  • A high A/F 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, P0172, P0174 OR P0175)


    1. Connect the intelligent tester to the DLC3.

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

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

    4. Read DTCs.

      Result
      Result Proceed to
      P0171, P0172, P0174 or P0175 is output A
      P0171, P0172, P0174 or P0175 and other DTCs are output 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. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (A/F CONTROL)


    1. Connect the intelligent tester to the DLC3.

    2. Start the engine and turn the 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 operation with the engine idling.

    6. Monitor the output voltages of A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the tester.

      Result
      The A/F sensor reacts in accordance with increases and decreases in the fuel injection volume:
      +12.5% = Rich output
      Below 3.1 V
      -12.5% = Lean output
      Higher than 3.4 V

      Note

      The A/F sensor has an output delay of a few seconds and the HO2 sensor 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 A01EQ75E08 A01EOHQE08 A01EQ75E08 A01EOEIE06 -
      2 A01EQ75E08 A01ERBDE01 A01EQ75E08 A01EOEIE06

      • A/F sensor

      • A/F sensor heater

      • A/F sensor circuit
      3 A01EQ75E08 A01ERBDE01 A01EQ75E08 A01ERBDE01

      • Fuel injector

      • Fuel pressure

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

      • Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.

      • To display the graph, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Data List / All Data / AFS Voltage B1S1 and O2SB1 S2 or AFS Voltage B2S1 and O2S B2S2.

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

    B

    Click here

    C

    PERFORM CONFIRMATION DRIVING PATTERN Click here

    A

  3. INSPECT MASS AIR FLOW METER


    1. Inspect the mass air flow meter Click here.


    NG

    REPLACE MASS AIR FLOW METER Click here

    OK

  4. READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)


    1. Connect the intelligent tester to the DLC3.

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

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

  5. 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 Click here

    OK

  6. CHECK AIR INDUCTION SYSTEM


    1. Check the air induction system for vacuum leakage Click here.

      OK
      No leakage from air induction system.

    NG

    REPAIR OR REPLACE AIR INDUCTION SYSTEM Click here

    OK

  7. CHECK FOR SPARKS AND IGNITION


    1. Disconnect the injector connectors to prevent the engine from starting.

      CAUTION:

      Always disconnect all injector connectors.

      Note

      Do not crank the engine for more than 2 seconds.

    2. Remove the ignition coil from the cylinder head Click here.

    3. A01EPJA

      Install the spark plug onto the ignition coil.

    4. Attach the spark plug assembly to the cylinder head.

    5. Crank the engine for less than 2 seconds and check the spark.

      OK
      Sparks jump across electrode gap.

    6. Install the ignition coil.

    7. Reconnect the injector connectors.


    NG

    REPAIR OR REPLACE IGNITION SYSTEM Click here

    OK

  8. CHECK FOR EXHAUST GAS LEAK


    1. Check for exhaust gas leakage.

      OK
      No gas leakage.

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  10. INSPECT FUEL INJECTOR (INJECTION AND VOLUME)


    1. Check the injection volume Click here.


    NG

    REPLACE FUEL INJECTOR Click here

    OK

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

    A01ERHXE06

    1. Disconnect the Air Fuel ratio (A/F) 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
      1 (HA2A) - 2 (+B) 20°C (68°F) 1.8 to 3.4 Ω
      1 (HA2A) - 4 (A2A-) Always 10 kΩ or higher

    NG

    REPLACE AIR FUEL RATIO SENSOR Click here

    OK

  12. INSPECT INTEGRATION RELAY (A/F RELAY)


    1. Remove the integration relay from the engine room relay block.

    2. A01EN9SE04

      Inspect the A/F fuse.


      1. Remove the A/F fuse from the integration relay.

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

        Standard Resistance
        Tester Connection Condition Specified Condition
        A/F fuse Always Below 1 Ω

      3. Reinstall the A/F fuse.

    3. Inspect the integration relay (A/F).


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

        Standard Resistance
        Tester Connection Condition Specified Condition
        1C-1 - 1A-4 No battery voltage applied to terminals 1A-2 and 1A-3 10 kΩ or higher
        Battery voltage applied to terminals 1A-2 and 1A-3 Below 1 Ω

    NG

    REPLACE INTEGRATION RELAY

    OK

  13. CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)


    1. Disconnect the Air Fuel ratio (A/F) sensor connector.

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      C47-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V
      C48-2 (+B) - Body ground Engine switch on (IG) 11 to 14 V

    3. Turn the engine switch off.

    4. Disconnect the ECM connector.

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

      Standard Resistance
      for LHD
      Tester Connection Condition Specified Condition
      C47-1 (HA1A) - C53-22 (HA1A) Always Below 1 Ω
      C47-3 (A1A+) - C53-126 (A1A+) Always Below 1 Ω
      C47-4 (A1A-) - C53-125 (A1A-) Always Below 1 Ω
      C48-1 (HA2A) - C53-20 (HA2A) Always Below 1 Ω
      C48-3 (A2A+) - C53-103 (A2A+) Always Below 1 Ω
      C48-4 (A2A-) - C53-102 (A2A-) Always Below 1 Ω
      C47-1 (HA1A) or C53-22 (HA1A) - Body ground Always 10 kΩ or higher
      C47-3 (A1A+) or C53-126 (A1A+) - Body ground Always 10 kΩ or higher
      C47-4 (A1A-) or C53-125 (A1A-) - Body ground Always 10 kΩ or higher
      C48-1 (HA2A) or C53-20 (HA2A) - Body ground Always 10 kΩ or higher
      C48-3 (A2A+) or C53-103 (A2A+) - Body ground Always 10 kΩ or higher
      C48-4 (A2A-) or C53-102 (A2A-) - Body ground Always 10 kΩ or higher
      for RHD
      Tester Connection Condition Specified Condition
      C47-1 (HA1A) - C54-22 (HA1A) Always Below 1 Ω
      C47-3 (A1A+) - C54-126 (A1A+) Always Below 1 Ω
      C47-4 (A1A-) - C54-125 (A1A-) Always Below 1 Ω
      C48-1 (HA2A) - C54-20 (HA2A) Always Below 1 Ω
      C48-3 (A2A+) - C54-103 (A2A+) Always Below 1 Ω
      C48-4 (A2A-) - C54-102 (A2A-) Always Below 1 Ω
      C47-1 (HA1A) or C54-22 (HA1A) - Body ground Always 10 kΩ or higher
      C47-3 (A1A+) or C54-126 (A1A+) - Body ground Always 10 kΩ or higher
      C47-4 (A1A-) or C54-125 (A1A-) - Body ground Always 10 kΩ or higher
      C48-1 (HA2A) or C54-20 (HA2A) - Body ground Always 10 kΩ or higher
      C48-3 (A2A+) or C54-103 (A2A+) - Body ground Always 10 kΩ or higher
      C48-4 (A2A-) or C54-102 (A2A-) - Body ground Always 10 kΩ or higher

    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

    A01ER7TE08

    • (a) Connect the intelligent tester to the DLC3.

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

    • (c) Clear DTCs Click here.

    • (d) Switch the ECM from normal mode to check mode using the tester Click here.

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

    • (f) 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.

      Tech Tips

      If the system is still malfunctioning, the MIL will be illuminated during step (f).

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

    2. Read DTCs.

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

    B

    REPLACE ECM Click here

    A

    END