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P0171 P0172

DTC    P0171    System Too Lean (Bank 1)

DTC    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).
  1. Intake system
  2. Fuel injector assembly
  3. Mass air flow meter sub-assembly
  4. Engine coolant temperature sensor
  5. Fuel pressure
  6. Gas leaks from exhaust system
  7. Open or short in air fuel ratio sensor (sensor 1) circuit
  8. Air fuel ratio sensor (sensor 1)
  9. Air fuel ratio sensor heater (sensor 1)
  10. PCV valve and hose
  11. PCV hose connections
  12. EGR valve assembly
  13. ECM
  14. Wire harness or connector
P0172 With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to rich side (2 trip detection logic).
  1. Fuel injector assembly
  2. Mass air flow meter sub-assembly
  3. Engine coolant temperature sensor
  4. Ignition system
  5. Fuel pressure
  6. Gas leaks from exhaust system
  7. Open or short in air fuel ratio sensor (sensor 1) circuit
  8. Air fuel ratio sensor (sensor 1)
  9. Air fuel ratio sensor heater (sensor 1)
  10. EGR valve assembly
  11. ECM
  12. Wire harness or connector

HINT:

  1. 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.
  2. If the vehicle runs out of fuel, the air fuel ratio is lean and DTC P0171 may be set. The MIL then illuminates.
  3. 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, 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.


P0171 P0172 / Lexus CT200h / ZWA10



 

MONITOR STRATEGY

 

Required Sensors/Components Air fuel ratio sensor
Mass air flow meter sub-assembly
Crankshaft position sensor
Frequency of Operation Continuous


 

TYPICAL ENABLING CONDITIONS

 

Fuel system status Closed-loop
Auxiliary battery voltage 11 V or higher
Either of the following conditions 1 or 2 is set -
1. Engine speed Less than 1100 rpm
2. Intake air amount per revolution 0.12 g/rev or more


 

TYPICAL MALFUNCTION THRESHOLDS

 

Purge-cut Executing
Either of the following conditions 1 or 2 is met -
1. Average between short-term fuel trim and long-term fuel trim 35% or more (varies with engine coolant temperature)
2. Average between short-term fuel trim and long-term fuel trim -35% or less (varies with engine coolant temperature)


 

CONFIRMATION DRIVING PATTERN


P0171 P0172 / Lexus CT200h / ZWA10

 

  1. Connect the intelligent tester to the DLC3.
  2. Turn the power switch on (IG) and turn the tester on.
  3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation).
  4. Turn the power switch off and wait for 30 seconds.
  5. Turn the power switch on (IG) and turn the tester on [A].
  6. Put the engine in inspection mode (maintenance mode).
  7. Start the engine and warm it up (until the engine coolant temperature is 75°C (167°F) or higher) with all the accessories switched off [B].
  8. With the engine warmed up, idle the engine for 2 minutes or more [C].
  9. Drive the vehicle at between 75 and 120 km/h (47 and 75 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes or more [D].

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

     

  10. Enter the following menus: Powertrain / Engine and ECT / DTC.
  11. Read the pending DTC [E].

    HINT:

    1. If a pending DTC is output, the system is malfunctioning.

    WIRING DIAGRAM

Air fuel ratio sensor circuit: Refer to DTC P2195 .
Mass air flow meter circuit: Refer to DTC P0102 .

 

INSPECTION PROCEDURE

HINT:

  1. 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.
  2. 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.
  3. 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.
  4. Sensor 1 refers to the sensor closest to the engine assembly.
  5. Sensor 2 refers to the sensor farthest away from the engine assembly.
1.CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)
  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

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

  1. Read the DTCs.

    Result 
    Result Proceed to
    DTC P0171 or P0172 is output A
    DTC P0171 or P0172 and other DTCs are output B

    HINT:

    If any DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.
  B
GO TO DTC CHART
 
A  
 

 

2.CHECK PCV HOSE CONNECTIONS
  1. Inspect the PCV hose connections.

    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.

    OK:

    No leaks in intake system.
  NG
REPAIR OR REPLACE INTAKE SYSTEM
 
OK  
 

 

4.PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME)
  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Put the engine in inspection mode (maintenance mode).

  1. Start the engine.

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

  1. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.

  1. Perform the Control the Injection Volume operation with the engine idling.

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

    HINT:

    1. Change the fuel injection volume within the range of -12.0% to +12.0%. The injection volume can be changed in fine gradations.
    2. 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.
    3. If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

     

    Standard 
    Tester Display (Sensor) Injection Volume Status Voltage
    AFS Voltage B1S1
    (Air fuel ratio)
    +12% Rich Below 3.1 V
    AFS Voltage B1S1
    (Air fuel ratio)
    -12% Lean Higher than 3.4 V
    O2S B1S2
    (Heated oxygen)
    +12% Rich Higher than 0.55 V
    O2S B1S2
    (Heated oxygen)
    -12% Lean Below 0.4 V
     
    Result 
    Status of AFS Voltage B1S1 Status of O2S B1S2 Air Fuel Ratio Condition and Air Fuel Ratio Sensor Condition Misfire Suspected Trouble Area Proceed to
    Lean/Rich Lean/Rich Normal - - A
    Lean Lean Actual air fuel ratio lean May occur
    1. PCV valve and hose
    2. PCV hose connections
    3. Fuel injector assembly blockage
    4. Gas leaks from exhaust system
    5. Intake system
    6. Fuel pressure
    7. Mass air flow meter sub-assembly
    8. Engine coolant temperature sensor
    9. EGR valve assembly
    A
    Rich Rich Actual air fuel ratio rich -
    1. Fuel injector assembly leakage or blockage
    2. Gas leaks from exhaust system
    3. Ignition system
    4. Fuel pressure
    5. Mass air flow meter sub-assembly
    6. Engine coolant temperature sensor
    A
    Lean Lean/Rich Air fuel ratio sensor malfunction -
    1. Air fuel ratio sensor
    2. EGR valve assembly
    B
    Rich Lean/Rich Air fuel ratio sensor malfunction - Air fuel ratio sensor B
    Lean: During the Control the Injection Volume Active Test, the air fuel ratio sensor output voltage (AFS Voltage) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.
    Rich: During the Control the Injection Volume Active Test, the AFS Voltage is consistently below 3.1 V, and the O2S is consistently higher than 0.55 V.
    Lean/Rich: During the Control the Injection Volume Active Test, the output voltage of the heated oxygen sensor alternates correctly.

    HINT:

    Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2].
  B
Go to step 11
 
A  
 

 

5.READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)
  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

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

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

    Standard 
    Tester Display Condition Specified Condition
    Coolant Temp Cold engine Same as ambient air temperature
    Warm engine Between 75 and 100°C (167 and 212°F)
  NG
REPLACE ENGINE COOLANT TEMPERATURE SENSOR 
 
OK  
 

 

6.READ VALUE USING INTELLIGENT TESTER (MAF)
  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Put the engine in inspection mode (maintenance mode).

  1. Start the engine.

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

  1. Allow the engine to idle until Coolant Temp reaches 75°C (167°F) or higher.

  1. Read MAF with the engine speed at 2500 rpm.
     

    Standard 
    Tester Display Condition Specified Condition
    MAF Shift lever position: P
    Engine Speed: 2500 rpm
    Between 4.5 gm/sec. and 8.5 gm/sec.

     

 

  NG
Go to step 18
 
OK  
 

 

7.CHECK FUEL PRESSURE
  1. Check the fuel pressure.

  NG
REPAIR OR REPLACE FUEL SYSTEM
 
OK  
 

 

8.CHECK FOR EXHAUST GAS LEAK
  1. Check for exhaust gas leaks.

    OK:

    No gas leaks.
  NG
REPAIR OR REPLACE EXHAUST SYSTEM
 
OK  
 

 

9.CHECK FOR SPARKS AND IGNITION
  1. Perform a spark test.

HINT:

  1. Refer to the ignition system inspection procedure.
  2. If the spark plugs or ignition system malfunctions, engine misfire 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)
  1. Check the injection and volume.

HINT:

  1. Refer to the fuel injector assembly inspection procedure .
  2. If the injectors malfunction, engine misfire 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).
  OK
Go to step 15
 
  NG
REPLACE FUEL INJECTOR ASSEMBLY
 

 

11.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
  1. Inspect the air fuel ratio sensor.

  NG
REPLACE AIR FUEL RATIO SENSOR
 
OK  
 

 

12.CHECK TERMINAL VOLTAGE (+B OF AIR FUEL RATIO SENSOR)


 

P0171 P0172 / Lexus CT200h / ZWA10
  1. Disconnect the air fuel ratio sensor connector.

  1. Turn the power switch on (IG).

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

    Standard Voltage:

    Tester Connection Switch Condition Specified Condition
    D23-2 (+B) - Body ground Power switch on (IG) 11 to 14 V
    Text in Illustration 
    *a Front view of wire harness connector
    (to Air Fuel Ratio Sensor (Sensor 1))
  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.

  1. Disconnect the ECM connector.

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

    Standard Resistance:

     
    Tester Connection Condition Specified Condition
    D23-1 (HA1A) - D27-18 (HA1A) Always Below 1 Ω
    D23-3 (A1A+) - D27-103 (A1A+) Always Below 1 Ω
    D23-4 (A1A-) - D27-126 (A1A-) Always Below 1 Ω
    D23-1 (HA1A) or D27-18 (HA1A) - Body ground Always 10 kΩ or higher
    D23-3 (A1A+) or D27-103 (A1A+) - Body ground Always 10 kΩ or higher
    D23-4 (A1A-) or D27-126 (A1A-) - 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.

NEXT  
 

 

15.PERFORM CONFIRMATION DRIVING PATTERN
  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Clear the DTCs .

  1. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.

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

  1. Read the pending DTCs.

    Result 
    Result Proceed to
    DTC P0171 or P0172 is output A
    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.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Put the engine in inspection mode (maintenance mode).

  1. Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

    HINT:

    The A/C switch and all accessory switches should be off.

     

     

  1. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Data List / All Data / Throttle Idle Position and MAP.

  1. Confirm that the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

    HINT:

    1. Do not leave the EGR valve open for 10 seconds or more during the Active Test.
    2. Be sure to return the EGR valve to step 0 when the Active Test is completed.
    3. Do not open the EGR valve 30 steps or more during the Active Test.

    OK:

    MAP and idling condition 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
    Idling condition Steady idling Idling changes from steady to rough idling or stalls
    MAP
    (Data List)
    MAP value is 20 to 40 kPa (150 to 300 mmHg)
    (EGR valve is fully closed)
    MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

    HINT:

    During Active Test, if the idling condition does not change in response to EGR step position, then there is probably a malfunction in the EGR valve.
  OK
Go to step 18
 
  NG
Go to step 17
 

 

17.INSPECT EGR VALVE ASSEMBLY
  1. Remove the EGR valve assembly.

  1. Check if the EGR valve is stuck open.

    OK:

    EGR valve is tightly closed.
  NG
REPLACE EGR VALVE ASSEMBLY
 
OK  
 

 

18.CHECK HARNESS AND CONNECTOR
  1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter sub-assembly and ECM.

    HINT:

    Repair any problems.
NEXT  
 

 

19.CHECK WHETHER DTC OUTPUT RECURS
  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Clear the DTCs.

  1. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.

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

  1. Read the pending DTCs.

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

 

20.CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY - ECM)
  1. Disconnect the mass air flow meter sub-assembly connector.

  1. Disconnect the ECM connector.

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

     
    Tester Connection Condition Specified Condition
    D5-5 (VG) - D27-94 (VG) Always Below 1 Ω
    D5-4 (E2G) - D27-117 (E2G) Always Below 1 Ω
    D5-5 (VG) or D27-94 (VG) - Body ground Always 10 kΩ or higher
  NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
 
OK  
 

 

21.REPLACE MASS AIR FLOW METER SUB-ASSEMBLY
  1. Replace the mass air flow meter sub-assembly.

    HINT:

    If the result of the inspection performed in step 6 indicated no problem, proceed to the next step without replacing the mass air flow meter sub-assembly.
NEXT  
 

 

22.CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED
  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Turn the tester on.

  1. Clear the DTC.

  1. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.

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

  1. Read the pending DTCs.

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