1Nz-Fe Engine Control. Dtc P0171 System Too Lean (Bank 1)

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 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 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 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 a warm engine and stable air fuel ratio feedback, the fuel trim is considerably in error to the lean side (2 trip detection logic).	Intake system Fuel injector blockage Mass air flow meter Engine coolant temperature sensor Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor (bank 1 sensor 1) circuit Air fuel ratio sensor (bank 1 sensor 1) PCV valve and hose PCV hose connections ECM Wire harness or connector
P0172	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).	Fuel injector leak or blockage Mass air flow meter Engine coolant temperature sensor Ignition system Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor (bank 1 sensor 1) circuit Air fuel ratio sensor (bank 1 sensor 1) ECM Wire harness or connector

HINT:

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.
If the vehicle runs out of fuel, the air fuel ratio is lean and DTC P0171 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 fuel injection volumes estimated by the ECM 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:
The average fuel trim learned value is more than +35% or less than -35%, 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)	Air fuel ratio 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

Fuel-trim:
Monitor runs whenever following DTCs not present	P0010 (Camshaft Timing Oil Control Valve) P0011 (VVT System - Advance) P0012 (VVT System - Retard) P0016 (VVT System - Misalignment) P0031, P0032, P101D (Air Fuel Ratio Sensor Heater) P0102, P0103 (Mass Air Flow Meter) P0115, P0117, P0118 (Engine Coolant Temperature Sensor) P0125 (Insufficient Coolant Temperature for Closed Loop Fuel Control) P0120, P0121, P0122, P0123, P0220, P0222, P0223, P2135 (Throttle Position Sensor) P0335 (Crankshaft Position Sensor) P0340 (Camshaft Position Sensor) P0351 - P0354 (Igniter) P0500 (Vehicle Speed Sensor) P219A (Air Fuel Ratio Imbalance)
Fuel system status	Closed loop
Battery voltage	11 V or higher
Either of following conditions met	1 or 2
1. Engine speed	Less than 700 rpm
2. Engine load	16% or more
Catalyst monitor	Not executed

TYPICAL MALFUNCTION THRESHOLDS

Fuel-trim:
Purge-cut	Executing
Either of following conditions 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

Connect the Techstream to the DLC3.
Turn the ignition switch to ON and turn the Techstream on.
Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON and turn the Techstream on [A].
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].
With the engine warmed up, idle the engine for 2 minutes or more [C].
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.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [E].
Read pending DTCs.
HINT:
If a pending DTC is output, the system is malfunctioning.
If no pending DTC is output, perform a universal trip and check for permanent DTCs (YARIS_NCP93 RM000000PDK0T5X.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

Refer to DTC P0031 for the air fuel ratio sensor circuit (YARIS_NCP93 RM000000WC10MFX_07.html).
Refer to DTC P0102 for the mass air flow meter circuit (YARIS_NCP93 RM000000U5B0KEX_07.html).

INSPECTION PROCEDURE

NOTICE:

Inspect the fuses for circuits related to this system before performing the following inspection procedure.

HINT:

Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.
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.
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.

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

Connect the Techstream to the DLC3.

Turn the ignition switch to ON.

Turn the Techstream on.

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

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.

GO TO DTC CHART (YARIS_NCP93 RM000000PDF0EWX.html)

A

2.CHECK PCV HOSE CONNECTIONS

Check the PCV hose connections (YARIS_NCP93 RM000001RN103YX.html).
OK:
PCV valve and hose are connected correctly and are not damaged.

REPAIR OR REPLACE PCV HOSE (YARIS_NCP93 RM000001RN204OX.html)

OK

3.CHECK INTAKE SYSTEM

Check the intake system for vacuum leaks (YARIS_NCP93 RM000004VL8003X.html).
OK:
No leaks in intake system.
HINT:
Perform "Inspection After Repair" after repairing or replacing the intake system (YARIS_NCP93 RM000004NJD006X.html).

REPAIR OR REPLACE INTAKE SYSTEM

OK

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

Connect the Techstream to the DLC3.

Start the engine.

Turn the Techstream on.

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

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

Perform the Control the Injection Volume operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).

Monitor the voltage outputs of the air fuel ratio sensor and the heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the Techstream.

HINT:

Change the fuel injection volume within the range of -12% to +12%. The injection volume can be changed in fine gradations.
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.
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 (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 AFS Voltage B1S1	Status O2S B1S2	Air Fuel Ratio Condition and Air Fuel Ratio Sensor Condition	Suspected Trouble Area	Proceed to
Lean/Rich	Lean/Rich	Normal	-	A
Lean	Lean	Actual air fuel ratio lean	PCV valve and hose PCV hose connections Fuel injector blockage Gas leak from exhaust system Intake system Fuel pressure Mass air flow meter Engine coolant temperature sensor	A
Rich	Rich	Actual air fuel ratio rich	Fuel injector leak or blockage Gas leak from exhaust system Ignition system Fuel pressure Mass air flow meter Engine coolant temperature sensor	A
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	B

Lean: During Control the Injection Volume, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently below 0.4 V.
Rich: During Control the Injection Volume, the AFS Voltage B1S1 is consistently below 3.1 V, and the O2S B1S2 is consistently higher 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.

HINT:

Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2] (YARIS_NCP93 RM000000SXS05AX.html).

Go to step 11

A

5.READ VALUE USING TECHSTREAM (COOLANT TEMP)

Connect the Techstream to the DLC3.

Turn the ignition switch to ON.

Turn the Techstream on.

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

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 75 and 100°C (167 and 212°F)

HINT:

Perform "Inspection After Repair" after replacing the engine coolant temperature sensor (YARIS_NCP93 RM000004NJD006X.html).

REPLACE ENGINE COOLANT TEMPERATURE SENSOR (YARIS_NCP93 RM000003VID00IX.html)

OK

6.READ VALUE USING TECHSTREAM (MAF)

Connect the Techstream to the DLC3.

Turn the ignition switch to ON.

Turn the Techstream on.

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

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

Read MAF with the engine speed at 3000 rpm.

Standard:

Techstream Display
Condition
Specified Condition
MAF
Shift lever position: N
A/C: Off
Engine Speed: 3000 rpm
Between 4 gm/sec. and 10 gm/sec.

Go to step 16

OK

7.CHECK FUEL PRESSURE

Check the fuel pressure (YARIS_NCP93 RM000001IQZ080X_01_0002.html).
HINT:
Perform "Inspection After Repair" after repairing or replacing the fuel system (YARIS_NCP93 RM000004NJD006X.html).

REPAIR OR REPLACE FUEL SYSTEM

OK

8.CHECK FOR EXHAUST GAS LEAK

Check for exhaust gas leaks.
OK:
No gas leaks.
HINT:
Perform "Inspection After Repair" after repairing or replacing the exhaust system (YARIS_NCP93 RM000004NJD006X.html).

REPAIR OR REPLACE EXHAUST SYSTEM

OK

9.CHECK SPARK AND IGNITION

Perform a spark test (YARIS_NCP93 RM000001EFG05SX_01_0003.html).

HINT:

If the result of the spark test is normal, proceed to the next step.
If the spark plugs or ignition system malfunctions, 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).
Perform "Inspection After Repair" after repairing or replacing the ignition system (YARIS_NCP93 RM000004NJD006X.html).

NEXT

10.INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

Check the injection and volume.

HINT:

Refer to the fuel injector assembly inspection procedure (YARIS_NCP93 RM000001EDQ04MX.html).
If the 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).
Perform "Inspection After Repair" after replacing the fuel injector assembly (YARIS_NCP93 RM000004NJD006X.html).

Go to step 15

REPLACE FUEL INJECTOR ASSEMBLY (YARIS_NCP93 RM000001EDS04WX.html)

11.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Inspect the air fuel ratio sensor (YARIS_NCP93 RM000003VIJ00FX.html).
HINT:
Perform "Inspection After Repair" after replacing the air fuel ratio sensor (YARIS_NCP93 RM000004NJD006X.html).

REPLACE AIR FUEL RATIO SENSOR (YARIS_NCP93 RM000003VIL00HX.html)

OK

12.CHECK TERMINAL VOLTAGE (POWER SOURCE OF AIR FUEL RATIO SENSOR)

Disconnect the air fuel ratio sensor connector.

Turn the ignition switch to ON.

Measure the voltage according to the value(s) in the table below.
Standard Voltage:
Tester Connection
Switch Condition
Specified Condition
C56-2 (+B) - Body ground
Ignition switch ON
11 to 14 V
Text in Illustration
*a
Front view of wire harness connector
(to Air Fuel Ratio Sensor)

Go to step 21

OK

13.CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)

Disconnect the air fuel ratio sensor connector.

Disconnect the ECM connector.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
C56-1 (HA1A) - C51-23 (HA1A)	Always	Below 1 Ω
C56-3 (A1A+) - C51-133 (A1A+)	Always	Below 1 Ω
C56-4 (A1A-) - C51-134 (A1A-)	Always	Below 1 Ω
C56-1 (HA1A) or C51-23 (HA1A) - Body ground	Always	10 kΩ or higher
C56-3 (A1A+) or C51-133 (A1A+) - Body ground	Always	10 kΩ or higher
C56-4 (A1A-) or C51-134 (A1A-) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

14.REPLACE AIR FUEL RATIO SENSOR

Replace the air fuel ratio sensor (YARIS_NCP93 RM000003VIL00HX.html).
HINT:
Perform "Inspection After Repair" after replacing the air fuel ratio sensor (YARIS_NCP93 RM000004NJD006X.html).

NEXT

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

Connect the Techstream to the DLC3.

Turn the ignition switch to ON.

Turn the Techstream on.

Clear the DTCs (YARIS_NCP93 RM000000PDK0T5X.html).

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

Turn the ignition switch to ON.

Turn the Techstream on.

Start the engine and warm it up.

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

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

Read DTCs.

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

END

A

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

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)

Connect the Techstream to the DLC3.

Turn the ignition switch to ON.

Turn the Techstream on.

Clear the DTCs (YARIS_NCP93 RM000000PDK0T5X.html).

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

Turn the ignition switch to ON.

Turn the Techstream on.

Start the engine and warm it up.

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

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

Read DTCs.

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

END

A

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

Disconnect the mass air flow meter connector.

Disconnect the ECM connector.

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

Standard Resistance:

Tester Connection
Condition
Specified Condition
C63-3 (VG) - C51-91 (VG)
Always
Below 1 Ω
C63-2 (E2G) - C51-92 (E2G)
Always
Below 1 Ω
C63-3 (VG) or C51-91 (VG) - Body ground
Always
10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

19.REPLACE MASS AIR FLOW METER

Replace the mass air flow meter (YARIS_NCP93 RM000003VI000HX.html).
HINT:
1. 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.
2. Perform "Inspection After Repair" after replacing the mass air flow meter (YARIS_NCP93 RM000004NJD006X.html).

NEXT

20.CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

Connect the Techstream to the DLC3.

Turn the ignition switch to ON.

Turn the Techstream on.

Clear the DTCs (YARIS_NCP93 RM000000PDK0T5X.html).

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

Turn the ignition switch to ON.

Turn the Techstream on.

Start the engine and warm it up.

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

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

Read DTCs.

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

REPLACE ECM (YARIS_NCP93 RM000001CN002IX.html)

END

21.CHECK HARNESS AND CONNECTOR (NO. 1 INTEGRATION RELAY - AIR FUEL RATIO SENSOR)

Disconnect the air fuel ratio sensor connector.

Remove the No. 1 integration relay from the engine room relay block.

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

Standard Resistance:

Tester Connection
Condition
Specified Condition
C56-2 (+B) - 1E-4
Always
Below 1 Ω
C56-2 (+B) or 1E-4 - Body ground
Always
10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

CHECK ECM POWER SOURCE CIRCUIT (YARIS_NCP93 RM000001F7102NX.html)

Techstream Display	Condition	Specified Condition
Coolant Temp	Cold engine	Same as ambient air temperature
Coolant Temp	Warm engine	Between 75 and 100°C (167 and 212°F)

Tester Connection	Switch Condition	Specified Condition
C56-2 (+B) - Body ground	Ignition switch ON	11 to 14 V

Techstream Display	Condition	Specified Condition
MAF	Shift lever position: N A/C: Off Engine Speed: 3000 rpm	Between 4 gm/sec. and 10 gm/sec.