SFI SYSTEM, Diagnostic DTC:P0171, P0172

DTC Code DTC Name
P0171 System Too Lean (Fuel Trim)
P0172 System Too Rich (Fuel Trim)

DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim includes the short-term fuel trim and long-term fuel trim.

The short-term fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at its ideal theoretical value. The signal from the heated oxygen sensor indicates whether the air-fuel ratio is rich or lean compared to the ideal theoretical value, triggering a reduction in the fuel volume if the air-fuel ratio is rich, and an increase in the fuel volume if it is lean.

The long-term fuel trim is the overall fuel compensation in order to balance the short-term fuel trim for a continual deviation from the central value by individual engine differences, operating environment and age deterioration.

If both the short-term fuel trim and the long-term fuel trim are lean or rich beyond a standard level, it is detected as a malfunction in the SFI system. The ECM illuminates the MIL and a DTC is set.

DTC No. DTC Detection Condition Trouble Area
P0171 When air-fuel feedback is stable after warming up engine, fuel trim is considerably in error on lean side (2 trip detection logic)

  • Air induction system

  • Injector blockage

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Fuel pressure

  • Gas leakage in exhaust system

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

  • A/F sensor (sensor 1)

  • A/F sensor heater (sensor 1)

  • A/F relay

  • MAIN relay

  • PCV value and hose

  • PCV hose connection

  • ECM
P0172 When air-fuel feedback is stable after warming up engine, fuel trim is considerably in error on rich side (2 trip detection logic)

  • Injector leakage or blockage

  • Mass air flow meter

  • Engine coolant temperature sensor

  • Ignition system

  • Fuel pressure

  • Gas leakage in exhaust system

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

  • A/F sensor (sensor 1)

  • A/F sensor heater

  • A/F relay

  • MAIN relay

  • ECM

Tech Tips


  • When DTC P0171 is set, the actual air-fuel ratio is lean. When DTC P0172 is set, the actual air-fuel ratio is rich.

  • If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 may be set. The MIL then illuminates.

  • If the total of the short-term fuel trim value and long-term fuel trim value is within +- 34%, the system is functioning normally.

MONITOR DESCRIPTION

A01E1PSE11

Under closed-loop fuel control, fuel injection amounts that deviate from the ECM's estimated fuel amount will cause a change in the long-term fuel trim compensation value. This long-term fuel amount will cause a change in the long-term fuel trim compensation value. This long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. And, the deviation from the simulated fuel injection amount by the ECM affects the smoothed fuel trim learning value. The smoothed fuel trim learning value is the combination of smoothed short term fuel trim (fuel feedback compensation value) and smoothed long-term fuel trim (learning value of the air-fuel ratio). When the smoothed fuel trim learning value exceeds the DTC threshold, the ECM interprets this as a fault in the fuel system and sets a DTC.

Example:

When the smoothed fuel trim leaning value is more than + 34% or less than - 34%, the ECM interprets this as a failure in the fuel system.

WIRING DIAGRAM

Refer to DTC P2195 Click here.

INSPECTION PROCEDURE

Tech Tips

Intelligent tester only:

Malfunctioning areas can be identified by performing the "Control the Injection Volume" function provided in the Active Test. The "Control the Injection Volume" function can help to determine whether the Air-fuel Ratio (A/F) sensor, heated oxygen (HO2) sensor and other potential trouble areas are malfunctioning.

The following instructions describe how to conduct the "Control the Injection Volume" operation using 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 2,500 rpm for approximately 90 seconds.

  4. On the tester, select the following menu items: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.

  5. Perform the "Control the Injection Volume" operation with the engine in an idling condition (press the right or left button to change the fuel injection volume).

  6. Monitor the output voltage of the A/F and Heated oxygen sensors (AFS B1 S1 and O2S B1 S2) displayed on the tester.

Tech Tips


  • The "Control the Injection Volume" operation lowers the fuel injection volume by 12.5% or increases the injection volume by 24.8%.

  • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Standard

Tester Display

(Sensor)

 Injection Volume Status Voltage

AFS B1 S1

(A/F)

 + 24.8% Rich Less than 3.0 V

AFS B1 S1

(A/F)

 - 12.5% Lean More than 3.35 V

O2S B1 S1

(HO2)

 + 24.8% Rich More than 0.55 V

O2S B1 S1

(HO2)

 - 12.5% Lean Less than 0.4 V

Note

The A/F sensor output has a few seconds of delay and the heated oxygen sensor output has about 20 seconds of delay at maximum.

Case

A/F Sensor (Sensor 1)

Output Voltage

HO2 Sensor (Sensor 2)

Output Voltage

 Main Suspected Trouble Areas
1

Injection Volume

+24.8%

-12.5%

 A01DUZ5

Injection Volume

+24.8%

-12.5%

 A01DUZ5 -

Output Voltage

More than 3.35 V

Less than 3.0 V

 A01DW5S

Output Voltage

More than 0.55 V

Less than 0.4 V

 A01DVNA
2

Injection Volume

+24.8%

-12.5%

 A01DUZ5

Injection Volume

+24.8%

-12.5%

 A01DUZ5

  • A/F sensor

  • A/F sensor heater

  • A/F sensor circuit

Output Voltage

Almost

no reaction

 A01E300

Output Voltage

More than 0.55 V

Less than 0.4 V

 A01DVNA
3

Injection Volume

+24.8%

-12.5%

 A01DUZ5

Injection Volume

+24.8%

-12.5%

 A01DUZ5

  • HO2 sensor

  • HO2 sensor heater

  • HO2 sensor circuit

Output Voltage

More than 3.35 V

Less than 3.0 V

 A01DW5S

Output Voltage

Almost

no reaction

 A01E300
4

Injection volume

+24.8%

-12.5%

 A01DUZ5

Injection Volume

+24.8%

-12.5%

 A01DUZ5

  • Injector

  • Fuel pressure

  • Gas leakage from exhaust system

    (Air-fuel ratio extremely lean or rich)

Output Voltage

Almost

no reaction

 A01E300

Output Voltage

Almost

no reaction

 A01E300

Tech Tips


  • Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when malfunctions are detects. 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 the conditions that would cause the engine to run with the rich air-fuel mixture.

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

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 ON and turn the tester ON.

    3. Select the following menu items: Powertrain / Engine and ECT / DTC.

    4. Read DTCs.

      Result
      Display (DTC Output) Proceed to
      P0171 or P0172 A
      P0171 or P0172 and other DTCs B

      Tech Tips

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


    B

    GO TO RELEVANT DTC CHART

    A

  2. CHECK PCV HOSE

    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 from air induction system.

    NG

    REPAIR OR REPLACE AIR INDUCTION SYSTEM

    OK

  4. PERFORM ACTIVE TEST (CONTROL THE INJECTION VOLUME)


    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 2,500 rpm for approximately 90 seconds.

    4. On the tester, select the following menu items: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.

    5. Perform the Control the Injection Volume operation with the engine in an idling condition (press the right or left button to change the fuel injection volume).

    6. Monitor the output voltage of A/F and HO2 sensors (AFS B1 S1 and O2S B1 S2) displayed on the tester.

      Tech Tips


      • The "Control the Injection Volume" operation decreases the fuel injection volume by 12.5% or increases the injection volume by 24.8%.

      • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

      Standard

      Tester Display

      (Sensor)

      		 Injection Volume Status Voltage

      AFS B1 S1

      (A/F)

      		 + 24.8% Rich Less than 3.0 V

      AFS B1 S1

      (A/F)

      		 - 12.5% Lean More than 3.35 V

      O2S B1 S1

      (HO2)

      		 + 24.8% Rich More than 0.55 V

      O2S B1 S1

      (HO2)

      		 - 12.5% Lean Less than 0.4 V
      Result:

      Status

      AFS B1 S1

      Status

      O2S B1 S2

      		 A/F Condition and A/F Sensor Condition Misfire Suspected Trouble Areas Proceed to
      Lean / Rich Lean / Rich Normal - - C
      Lean Lean Actual air-fuel ratio lean May occur

      • PCV valve and hose

      • PCV hose connections

      • Injector blockage

      • Gas leakage from exhaust system

      • Air induction system

      • Fuel pressure

      • Mass Air Flow (MAF) meter

      • Engine coolant Temperature (ECT) sensor

      		 A
      Rich Rich Actual air-fuel ratio rich -

      • Injector leakage or blockage

      • Gas leakage from exhaust system

      • Ignition system

      • Fuel pressure

      • MAF meter

      • ECT sensor

      		 A
      Lean Lean / Rich A/F sensor malfunction -

      • A/F sensor

      		 B
      Rich Lean / Rich A/F sensor malfunction -

      • A/F sensor

      		 B

      • Lean: During the Control the Injection Volume Active Test, the A/F sensor output voltage (AFS) is consistently more than 3.35 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.

      • Rich: During the Control the Injection Volume Active Test, the AFS is consistently less than 3.0 V, and the O2S is consistently more than 0.55 V.


    B

    INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here

    C

    PERFORM CONFIRMATION DRIVING PATTERN Click here

    A

  5. READ VALUE USING DATA LIST (COOLANT TEMP)


    1. Connect the intelligent tester to the DLC3.

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

    3. Select the following menu items: Powertrain / Engine and ECT / Data List / Coolant Temp.

    4. Read the Coolant Temp value twice, when the engine is cold and also when warmed up.

      Standard
      With cold engine: Same as ambient air temperature.
      With warm engine: Between 75 and 95°C (167 and 203°F)

    NG

    REPLACE ENGINE COOLANT TEMPERATURE SENSOR

    OK

  6. READ VALUE USING DATA LIST (MAF)


    1. Connect the intelligent tester to the DLC3.

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

    3. Select the following menu items: Powertrain / Engine and ECT / Data List / MAF and Coolant Temp.

    4. Allow the engine to idle until the Coolant Temp value reaches 75°C (167°F) or more.

    5. Read the MAF with the engine in an idling condition and at an engine speed of 2,500 rpm.

      Standard
      MAF while engine idling: Between 1 and 4 g/sec. (shift position: N (for A/T), or neutral (for M/T); A/C: OFF).
      MAF at engine speed of 2,500 rpm: Between 4 and 15 g/sec. (shift position: neutral; A/C: OFF).

    NG

    REPLACE MASS AIR FLOW METER

    OK

  7. CHECK FUEL PRESSURE


    1. Check the fuel pressure Click here.


    NG

    REPAIR OR REPLACE FUEL SYSTEM

    OK

  8. CHECK FOR EXHAUST GAS LEAKAGE

    OK
    No gas leakage.

    NG

    REPAIR OR REPLACE EXHAUST SYSTEM

    OK

  9. CHECK FOR SPARK AND IGNITION

    Tech Tips

    If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using the intelligent tester. Select the following menu items: Powertrain / Engine and ECT / Data List / CYL #1 (to CYL #4).


    NG

    REPAIR OR REPLACE IGNITION SYSTEM

    OK

  10. INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

    Tech Tips

    If the injectors malfunction, engine misfire may occur. The misfire count can be read using the intelligent tester. Select the following menu items: Powertrain / Engine and ECT / Data List / CYL #1 (to CYL #4).


    NG

    REPLACE FUEL INJECTOR ASSEMBLY

    OK

  11. INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

    A01DVTYE06

    1. Disconnect the A18 A/F sensor connector.

    2. Measure the resistance between the terminals of the A/F sensor connector.

      Standard resistance
      Tester Connection Condition Specified Condition
      1 (HT1A) -2 (+B) 20°C (68°F) 1.8 to 3.4 Ω
      1 (HT1A) -4 (A1A-) Always 10 kΩ or higher

    NG

    REPLACE AIR FUEL RATIO SENSOR

    OK

  12. INSPECT A/F RELAY (Marking: A/F)

    A01DVNZE20

    1. Remove the A/F relay from the engine room relay block.

    2. Check the resistance of the relay.

      Standard resistance
      Tester Connection Specified Condition
      3 - 5 10 kΩ or higher
      3 - 5

      Below 1 Ω

      (when battery voltage is applied to terminals 1 and 2)

    NG

    REPLACE A/F RELAY

    OK

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

    A01DW7BE09

    1. Disconnect the A18 sensor connector.

    2. Disconnect the E12 ECM connector.

    3. Measure the resistance of the wire harness side connectors.

      Standard resistance
      Tester Connection Specified Condition
      A18-1 (HT1A) - E12-1 (HA1A) Below 1 Ω
      A18-3 (A1A+) - E12-21 (A1A+) Below 1 Ω
      A18-4 (A1A-) - E12-31 (A1A-) Below 1 Ω
      A18-1 (HT1A) or E12-1 (HA1A) - Body ground 10 kΩ or higher
      A18-3 (A1A+) or E12-21 (A1A+) - Body ground 10 kΩ or higher
      A18-4 (A1A-) or E12-31 (A1A-) - Body ground 10 kΩ or higher
      A01DVTJE17

    NG

    REPAIR OR REPLACE HARNESS AND CONNECTOR

    OK

  14. REPLACE AIR FUEL RATIO SENSOR


    NEXT

  15. PERFORM CONFIRMATION DRIVING PATTERN

    A01DX32E46

    (a) Connect the intelligent tester to the DLC3.

    (b) Turn the ignition switch ON and turn the tester ON.

    (c) Clear DTCs.

    (d) Change the ECM from normal mode to check mode using the tester.

    (e) Start the engine and warm it up with all the accessories turned OFF.

    (f) Drive the vehicle at between 60 and 120 km/h (38 and 75 mph) and at an engine speed of between 1,400 and 3,200 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 IF DTC OUTPUT RECURS (DTC P0171 OR P0172)


    1. On the intelligent tester, select the following menu items: Powertrain / Engine and ECT / DTC.

    2. Read DTCs.

      Result
      Display (DTC Output) Proceed to
      No output A
      P0171 or P0172 B

    B

    READ VALUE USING DATA LIST (COOLANT TEMP) Click here

    A

    END