Dtc P0171 System Too Lean (Bank 1)

Engine Hybrid System. Yaris. Ncp93, 131
1Nz-Fe Engine Control. Yaris. Ncp93, 131

DESCRIPTION

MONITOR DESCRIPTION

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

TYPICAL MALFUNCTION THRESHOLDS

CONFIRMATION DRIVING PATTERN

WIRING DIAGRAM

INSPECTION PROCEDURE

CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)

CHECK PCV HOSE CONNECTIONS

CHECK INTAKE SYSTEM

PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME)

READ VALUE USING TECHSTREAM (COOLANT TEMP)

READ VALUE USING TECHSTREAM (MAF)

CHECK FUEL PRESSURE

CHECK EXHAUST GAS LEAK

CHECK FOR SPARKS AND IGNITION

INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

INSPECT AIR-FUEL RATIO SENSOR (HEATER RESISTANCE)

CHECK TERMINAL VOLTAGE (POWER SOURCE OF A/F SENSOR)

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

REPLACE AIR-FUEL RATIO SENSOR

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER CONNECTOR)

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER - ECM)

REPLACE MASS AIR FLOW METER

CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

CHECK HARNESS AND CONNECTOR (INTEGRATION RELAY (EFI RELAY) - AIR FUEL RATIO SENSOR)

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 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 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 blockage
  3. Mass Air Flow (MAF) meter
  4. Engine Coolant Temperature (ECT) sensor
  5. Fuel pressure
  6. Gas leak from exhaust system
  7. Open or short in A/F sensor (sensor 1) circuit
  8. A/F sensor (sensor 1)
  9. A/F sensor heater (sensor 1)
  10. Integration relay (EFI relay)
  11. A/F sensor heater and EFI relay circuits
  12. PCV valve and hose
  13. PCV hose connections
  14. ECM
  15. 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 leak or blockage
  2. MAF meter
  3. ECT sensor
  4. Ignition system
  5. Fuel pressure
  6. Gas leak from exhaust system
  7. Open or short in A/F sensor (sensor 1) circuit
  8. A/F sensor (sensor 1)
  9. A/F sensor heater (sensor 1)
  10. Integration relay (EFI relay)
  11. A/F sensor heater and EFI relay circuits
  12. ECM
  13. Wire harness or connector
HINT:
  1. When DTC P0171 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 is stored, 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 stored. The MIL is then illuminated.
  3. When the total of the short-term and long-term fuel trim values is within 20% (and the engine coolant temperature is more 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 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 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.

Yaris. Ncp93, 131.1Nz-Fe Engine Control.Sfi System (For Sedan). Dtc P0171 System Too Lean (Bank 1)


MONITOR STRATEGY


Related DTCs
P0171: Fuel trim lean
P0172: Fuel trim rich
Required Sensors/Components (Main)
Fuel system
Required Sensors/Components (Related)
A/F sensor, Mass air flow meter, Crankshaft position sensor
Frequency of Operation
Continuous
Duration
Within 10 seconds
MIL Operation
2 driving cycles
Sequence of Operation
None

TYPICAL ENABLING CONDITIONS


Monitor runs whenever following DTCs not present
P0010 (VVT OCV)
P0011 (VVT System 1 - Advance)
P0012 (VVT System 1 - Retard)
P0016 (VVT system - misalignment)
P0031, P0032 (A/F sensor heater)
P0100, P0102, P0103 (MAF meter)
P0115, P0117, P0118 (ECT sensor)
P0120 - P0123, P0220, P0222, P0223, P2135 (TP sensor)
P0125 (Insufficient ECT for Closed Loop)
P0335 (CKP sensor)
P0340 (CMP sensor)
P0351 - P0354 (Igniter)
P0500 (VSS)
Fuel system status
Closed loop
Battery voltage
11 V or more
Either of following conditions 1 or 2 set
-
1. Engine RPM
Below 1100 rpm
2. Intake air amount per revolution
0.15 g/rev or more
Catalyst monitor
Not executed

TYPICAL MALFUNCTION THRESHOLDS


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

CONFIRMATION DRIVING PATTERN


Yaris. Ncp93, 131.1Nz-Fe Engine Control.Sfi System (For Sedan). Dtc P0171 System Too Lean (Bank 1)

  1. Connect the Techstream to the DLC3.
  2. Turn the ignition switch to ON and turn the Techstream on.
  3. Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).
  4. Turn the ignition switch off and wait for at least 30 seconds.
  5. Turn the ignition switch to ON and turn the Techstream on [A].
  6. 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].
  7. With the engine warmed up, idle the engine for 2 minutes or more [C].
  8. Drive the vehicle at a speed between 60 and 135 km/h (38 and 85 mph) for 5 minutes or more [D].
    CAUTION:
    When performing the confirmation driving pattern, obey all speed limits and traffic laws.
  9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [E].
  10. Read pending DTCs.
    HINT:
    If a pending DTC is output, the system is malfunctioning.
  11. If no pending DTC is output, perform a universal trip and check for permanent DTCs (YARIS_NCP93 RM000000PDK0QGX.html).
    HINT:
    1. If a permanent DTC is output, the system is malfunctioning.
    2. If no permanent DTC is output, the system is normal.

WIRING DIAGRAM


Yaris. Ncp93, 131.1Nz-Fe Engine Control.Sfi System (For Sedan). Dtc P0171 System Too Lean (Bank 1)


INSPECTION PROCEDURE

NOTICE:
Inspect the fuses for circuits related to this system before performing the following inspection procedure.
HINT:
  1. Read freeze frame data using the Techstream. 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 a Techstream to the DLC3.

  1. Turn the ignition switch to ON.

  1. Turn the Techstream on.

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

  1. Read 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 (YARIS_NCP93 RM000000PDF0E6X.html)
A


2.CHECK PCV HOSE CONNECTIONS

  1. Check the PCV hose connections (YARIS_NCP93 RM000001L6B007X.html).

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 leak.

    OK:
    No leak from intake system.


NG
REPAIR OR REPLACE INTAKE SYSTEM
OK


4.PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME)

  1. Connect the Techstream to the DLC3.

  1. Start the engine.

  1. Turn the Techstream on.

  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 in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).

  1. Monitor the voltage outputs of the Air-Fuel Ratio (A/F) sensor and the Heated Oxygen (HO2) sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the Techstream.

    HINT:
    1. Change the fuel injection volume within the range of - 12% to +12%. 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:

    Techstream Display
    (Sensor)
    		Injection Volume
    		Status
    		Voltage
    AFS Voltage B1S1
    (A/F)
    		+12%
    		Rich
    		Less than 3.1
    -12%
    		Lean
    		More than 3.4
    O2S B1S2
    (HO2)
    		+12%
    		Rich
    		 More than 0.55
    -12%
    		Lean
    		Less than 0.4

    Result
    Status
    AFS Voltage B1S1
    		Status
    O2S B1S2
    		A/F Condition and
    A/F Sensor Condition
    		Suspected Trouble Area
    		Proceed to
    Lean/Rich
    		Lean/Rich
    		Normal
    		-
    		A
    Lean
    		Lean
    		Actual air-fuel ratio lean
    1. PCV valve and hose
    2. PCV hose connections
    3. Fuel injector blockage
    4. Gas leak from exhaust system
    5. Intake system
    6. Fuel pressure
    7. Mass Air Flow (MAF) meter
    8. Engine Coolant Temperature (ECT) sensor
    		A
    Rich
    		Rich
    		Actual air-fuel ratio rich
    1. Fuel injector blockage or blockage
    2. Gas leak from exhaust system
    3. Ignition system
    4. Fuel pressure
    5. MAF meter
    6. ECT sensor
    		A
    Lean
    		Lean/Rich
    		A/F sensor malfunction
    1. A/F sensor
    		B
    Rich
    		Lean/Rich
    		A/F sensor malfunction
    1. A/F sensor
    		B
    Lean: During Control the Injection Volume, the A/F sensor output voltage (AFS Voltage B1S1) is consistently more than 3.4 V, and the HO2 sensor output voltage (O2S Voltage B1S1) is consistently less than 0.4 V.
    Rich: During Control the Injection Volume, the AFS is consistently less than 3.1 V, and the O2S is consistently more than 0.55 V.
    Lean/Rich: During Control the Injection Volume of the Active Test, the output voltage of the heated oxygen sensor alternates correctly.


B
Go to step 11
A


5.READ VALUE USING TECHSTREAM (COOLANT TEMP)

  1. Connect the Techstream to the DLC3.

  1. Turn the ignition switch to ON.

  1. Turn the Techstream 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:

    Techstream Display
    		Condition
    		Specified Condition
    Coolant Temp
    		Cold engine
    		Same as ambient air temperature
    Warm engine
    		Between 80 and 100°C (176 and 212°F)


NG
REPLACE ENGINE COOLANT TEMPERATURE SENSOR (YARIS_NCP93 RM000001DBH011X.html)
OK


6.READ VALUE USING TECHSTREAM (MAF)

  1. Connect the Techstream to the DLC3.

  1. Turn the ignition switch to ON.

  1. Turn the Techstream on.

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

  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:

    Techstream Display
    		Condition
    		Specified Condition
    MAF
    		Shift lever position: N
    A/C: Off
    Engine Speed: 2500 rpm
    		Between 2 gm/sec, and 6 gm/sec.


NG
Go to step 16
OK


7.CHECK FUEL PRESSURE

  1. Check the fuel pressure (YARIS_NCP93 RM000001EF100YX_01_0002.html).



NG
REPAIR OR REPLACE FUEL SYSTEM
OK


8.CHECK EXHAUST GAS LEAK

  1. Check for exhaust gas leak.

    OK:
    No exhaust gas leak.


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 (YARIS_NCP93 RM000001EFG05DX.html).
    2. If the spark plugs or ignition system malfunction, engine misfire may occur. The misfire count can be read using the Techstream. 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 inspection procedure (YARIS_NCP93 RM000001EDQ046X.html).
    2. If the fuel injectors malfunction, engine misfire may occur. The misfire count can be read using the Techstream. 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 (YARIS_NCP93 RM000001EDS04FX.html)

11.INSPECT AIR-FUEL RATIO SENSOR (HEATER RESISTANCE)
Yaris. Ncp93, 131.1Nz-Fe Engine Control.Sfi System (For Sedan). Dtc P0171 System Too Lean (Bank 1)

  1. Disconnect the C23 A/F sensor connector.

  1. Measure the resistance of the A/F sensor connector.

    Standard resistance:
    Tester Connections
    		Specified Conditions
    HA1A (1) - +B (2)
    		1.8 Ω to 3.4 Ω at 20°C (68°F)
    HA1A (1) - A1A- (4)
    		10 kΩ or higher

  1. Reconnect the A/F sensor connector.



NG
REPLACE AIR-FUEL RATIO SENSOR (YARIS_NCP93 RM000001CKA00YX.html)
OK


12.CHECK TERMINAL VOLTAGE (POWER SOURCE OF A/F SENSOR)
Yaris. Ncp93, 131.1Nz-Fe Engine Control.Sfi System (For Sedan). Dtc P0171 System Too Lean (Bank 1)

  1. Disconnect the C23 A/F sensor connector.

  1. Turn the ignition switch to ON.

  1. Measure the voltage between the terminals of the C23 A/F sensor connector and body ground.

    Standard voltage:
    Tester Connections
    		Specified Conditions
    +B (C23-2) - Body ground
    		11 to 14 V
    Result
    Result
    		Proceed to
    NG
    		A
    OK
    		B

  1. Reconnect the A/F sensor connector.



NG
Go to step 21
OK


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

  1. Disconnect the A/F sensor connector.

  1. Disconnect the ECM connector.

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

    Standard Resistance (Check for Open):
    Tester Connection
    		Condition
    		Specified Condition
    HA1A (C23-1) - HA1A (C20-109)
    		Always
    		Below 1 Ω
    A1A+ (C23-3) - A1A+ (C20-112)
    		Always
    		Below 1 Ω
    A1A- (C23-4) - A1A- (C20-113)
    		Always
    		Below 1 Ω
    Standard Resistance (Check for Short):
    Tester Connection
    		Condition
    		Specified Condition
    HA1A (C23-1) - HA1A (C20-109) Body ground
    		Always
    		10 kΩ or higher
    A1A+ (C23-3) - A1A+ (C20-112) Body ground
    		Always
    		10 kΩ or higher
    A1A- (C23-4) - A1A- (C20-113) Body ground
    		Always
    		10 kΩ or higher

  1. Reconnect the ECM connector.

  1. Reconnect the A/F sensor connector.



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK


14.REPLACE AIR-FUEL RATIO SENSOR

  1. Replace the A/F sensor (YARIS_NCP93 RM000001CKA00YX.html).


NEXT


15.CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

  1. Connect the Techstream to the DLC3.

  1. Turn the ignition switch ON.

  1. Turn the Techstream on.

  1. Clear DTCs (YARIS_NCP93 RM000000PDK0QGX.html).

  1. Turn the ignition switch off.

  1. Turn the ignition switch ON.

  1. Turn the Techstream on.

  1. Start the engine and warm it up.

  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 / Trouble Codes.

  1. Read DTCs.

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


B
END
A


16.CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER CONNECTOR)

  1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM (YARIS_NCP93 RM000000UZ309WX.html).

    HINT:
    Repair any problems.

NEXT


17.CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

  1. Connect the Techstream to the DLC3.

  1. Turn the ignition switch ON.

  1. Turn the Techstream on.

  1. Clear DTCs (YARIS_NCP93 RM000000PDK0QGX.html).

  1. Turn the ignition switch off and wait for at least 30 seconds.

  1. Turn the ignition switch to ON.

  1. Turn the Techstream on.

  1. Start the engine and warm it up.

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

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

  1. Read DTCs.

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


B
END
A


18.CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER - ECM)

  1. Disconnect the mass air flow meter connector.

  1. Disconnect the ECM connector.

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

    Standard Resistance (Check for Open):
    Tester Connection
    		Condition
    		Specified Condition
    C26-3 (VG) - C20-118 (VG)
    		Always
    		Below 1 Ω
    C26-2 (E2G) - C20-116 (E2G)
    Standard Resistance (Check for Short):
    Tester Connection
    		Condition
    		Specified Condition
    C26-3 (VG) or C20-118 (VG) - Body ground
    		Always
    		10 kΩ or higher

  1. Reconnect the mass air flow meter connector.

  1. Reconnect the ECM connector.



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK


19.REPLACE MASS AIR FLOW METER

  1. Replace the mass air flow meter (YARIS_NCP93 RM000001D0L00WX.html).

    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.

NEXT


20.CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

  1. Connect the Techstream to the DLC3.

  1. Turn the ignition switch ON.

  1. Turn the Techstream on.

  1. Clear DTCs (YARIS_NCP93 RM000000PDK0QGX.html).

  1. Turn the ignition switch off and wait for at least 30 seconds.

  1. Turn the ignition switch to ON.

  1. Turn the Techstream on.

  1. Start the engine and warm it up.

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

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

  1. Read DTCs.

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


B
REPLACE ECM
A

END

21.CHECK HARNESS AND CONNECTOR (INTEGRATION RELAY (EFI RELAY) - AIR FUEL RATIO SENSOR)
Yaris. Ncp93, 131.1Nz-Fe Engine Control.Sfi System (For Sedan). Dtc P0171 System Too Lean (Bank 1)

  1. Disconnect the C23 A/F sensor connector.

  1. Remove the integration relay from the engine room Relay Block (R/B).

  1. Check the resistance.

    Standard resistance (Check for open):
    Tester Connections
    		Specified Conditions
    +B (C23-2) - Engine room R/B (1A-4)
    		Below 1 Ω
    Standard resistance (Check for short):
    Tester Connections
    		Specified Conditions
    +B (C23-2) or Engine room
    R/B (1A-4) - Body ground
    		10 kΩ or higher

  1. Reconnect the A/F sensor connector.

  1. Reinstall the integration relay.



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

CHECK ECM POWER SOURCE CIRCUIT