Lexus NX: System Too Lean (Bank 1) (P0171,P0172)

Lexus NX Service Manual / Engine & Hybrid System / 2ar-fxe (engine Control) / Sfi System / System Too Lean (Bank 1) (P0171,P0172)

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 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.	Detection Item	DTC Detection Condition	Trouble Area	MIL	Memory
P0171	System Too Lean (Bank 1)	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 assembly Mass air flow meter sub-assembly Engine coolant temperature sensor Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor (sensor 1) circuit Air fuel ratio sensor (sensor 1) PCV valve and hose PCV hose connections EGR valve assembly Wire harness or connector ECM	Comes on	DTC stored
P0172	System Too Rich (Bank 1)	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 assembly Mass air flow meter sub-assembly Engine coolant temperature sensor Ignition system Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor (sensor 1) circuit Air fuel ratio sensor (sensor 1) EGR valve assembly Wire harness or connector ECM	Comes on	DTC stored

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 73°C [163°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 +35% or higher, or -35% or less, the ECM interprets this as a fuel system malfunction.

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 sub-assembly 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 the following DTCs are not stored	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) P0107, P0108 (Manifold absolute pressure) P0115, P0117, P0118 (Engine coolant temperature sensor) P0120, P0121, P0122, P0123, P0220, P0222, P0223, P2135 (Throttle position sensor) P0125 (Insufficient coolant temperature for closed loop fuel control) P0335 (Crankshaft position sensor) P0340 (Camshaft position sensor) P0340, P0342, P0343 (VVT sensor) P0351, P0352, P0353, P0354 (Igniter) P0401 (EGR system) P219A, P219C, P219D, P219E, P219F (Air-fuel ratio imbalance)
Fuel system status	Closed loop
Auxiliary battery voltage	11 V or higher
Either of the following conditions is met	1 or 2
1. Engine speed	Less than 1100 rpm
2. Engine load	10% or more
Catalyst monitor	Not executed

TYPICAL MALFUNCTION THRESHOLDS

P0171 and P0172: Fuel-Trim Lean/Rich

EVAP purge-cut	Executing
Either of the following conditions is met	1 or 2
1. Average between short-term fuel trim and long-term fuel trim	35% or higher (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 power switch on (IG) and turn the Techstream on.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
Turn the power switch off and wait for at least 30 seconds.
Turn the power switch on (IG) and turn the Techstream on [A].
Put the engine in inspection mode (maintenance mode).
Click here
Start the engine and warm it up until the engine coolant temperature is 73°C (163°F) or higher with all the accessories switched off [B].
With the engine warmed up, idle the engine for 5 minutes or more [C].
With the engine running, drive the vehicle at a speed between 75 and 120 km/h (47 and 75 mph) for 5 minutes or more [D].
CAUTION:

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

HINT:

If the engine stops, further depress the accelerator pedal to restart the engine.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes [E].
Read the 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.
Click here
HINT:
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.

WIRING DIAGRAM

Refer to DTC P0102 for the mass air flow meter sub-assembly circuit.

Click here

Refer to DTC P2195 for the air fuel ratio sensor circuit.

Click here

CAUTION / NOTICE / HINT

NOTICE:

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

PROCEDURE

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

(a) Connect the Techstream to the DLC3

(b) Turn the power switch on (IG).

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

(e) Read the DTCs.

Powertrain > Engine and ECT > Trouble Codes

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

2.	CHECK PCV HOSE CONNECTIONS

(a) Check the PCV hose connections.

Click here

OK:

PCV valve and hose are connected correctly and are not damaged.

REPAIR OR REPLACE PCV HOSE

3.	CHECK INTAKE SYSTEM

(a) Check the intake system for vacuum leaks.

Click here

OK:

No leaks in intake system.

HINT:

Perform "Inspection After Repair" after repairing or replacing the intake system.

Click here

REPAIR OR REPLACE INTAKE SYSTEM

4.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

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

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

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

(f) Idle the engine for 5 minutes or more with the shift lever in P.

(g) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Gas AF Control / AFS Voltage B1S1 and O2S B1S2.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the Injection Volume for A/F Sensor

Data List Display
AFS Voltage B1S1
O2S B1S2

(h) Perform the Control the Injection Volume for A/F Sensor operation with the engine idling (press the 12.5% or -12.5% button to change the fuel injection volume).

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

HINT:

The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.
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)	12.5%	Rich	Below 3.1 V
AFS Voltage B1S1 (Air fuel ratio)	-12.5%	Lean	Higher than 3.4 V
O2S B1S2 (Heated oxygen)	12.5%	Rich	Higher than 0.55 V
O2S B1S2 (Heated oxygen)	-12.5%	Lean	Below 0.4 V

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 assembly blockage Gas leak from exhaust system Intake system Fuel pressure Mass air flow meter sub-assembly Engine coolant temperature sensor EGR valve assembly
Rich	Rich	Actual air fuel ratio rich	Fuel injector assembly leak or blockage Gas leak from exhaust system Ignition system Fuel pressure Mass air flow meter sub-assembly Engine coolant temperature sensor
Lean	Lean/Rich	Air fuel ratio sensor malfunction	Air fuel ratio sensor EGR valve assembly	B
Rich	Lean/Rich	Air fuel ratio sensor malfunction	Air fuel ratio sensor	B

Lean: During Control the Injection Volume for A/F Sensor Active Test, 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 for A/F Sensor Active Test, AFS Voltage B1S1 is consistently below 3.1 V, and O2S B1S2 is consistently higher than 0.55 V.
Lean/Rich: During Control the Injection Volume for A/F Sensor Active Test, the output voltage of the air fuel ratio sensor and the heated oxygen sensor alternate correctly.

HINT:

Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2].

Click here

GO TO STEP 11

5.	READ VALUE USING TECHSTREAM (COOLANT TEMP)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Enter the following menus: Powertrain / Engine and ECT / Data List / Primary / Coolant Temp.

Powertrain > Engine and ECT > Data List

Tester Display
Coolant Temp

(e) 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
Coolant Temp	Warm engine	Between 75 and 100°C (167 and 212°F)

HINT:

Perform "Inspection After Repair" after replacing the engine coolant temperature sensor.

Click here

REPLACE ENGINE COOLANT TEMPERATURE SENSOR

6.	READ VALUE USING TECHSTREAM (MAF)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

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

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine.

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

Powertrain > Engine and ECT > Data List

Tester Display
Engine Speed
MAF
Coolant Temp

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

(h) Read MAF with the engine speed at 2500 rpm.

Standard:

Techstream Display	Condition	Specified Condition
MAF	Shift lever position: P A/C: Off Engine Speed: 2500 rpm	Between 5 gm/sec and 9 gm/sec

Techstream Display

Condition

Specified Condition

MAF

Shift lever position: P

A/C: Off

Engine Speed: 2500 rpm

Between 5 gm/sec and 9 gm/sec

HINT:

During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, read the Data List item after charging control has completed.

GO TO STEP 18

7.	CHECK FUEL PRESSURE

(a) Check the fuel pressure.

Click here

REPAIR OR REPLACE FUEL SYSTEM

8.	CHECK FOR EXHAUST GAS LEAK

(a) Check for exhaust gas leaks.

OK:

No gas leaks.

HINT:

Perform "Inspection After Repair" after repairing or replacing the exhaust system.

Click here

REPAIR OR REPLACE EXHAUST SYSTEM

9.	CHECK FOR SPARK (SPARK TEST)

(a) Perform a spark test.

Click here

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 / Gas Misfire / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).
Perform "Inspection After Repair" after repairing or replacing the ignition system.
Click here

10.	INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

(a) Check the injection and volume.

HINT:

Refer to the fuel injector assembly inspection procedure.
Click here
If the fuel injector assemblies malfunction, engine misfire may occur. The misfire count can be read using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Gas Misfire / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).
Perform "Inspection After Repair" after replacing the fuel injector assembly.
Click here

GO TO STEP 15

REPLACE FUEL INJECTOR ASSEMBLY

11.	INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Click here

REPLACE AIR FUEL RATIO SENSOR

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

Click here

GO TO STEP 23

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

Click here

REPAIR OR REPLACE HARNESS OR CONNECTOR

14.	REPLACE AIR FUEL RATIO SENSOR

(a) Replace the air fuel ratio sensor.

Click here

HINT:

Perform "Inspection After Repair" after replacing the air fuel ratio sensor.

Click here

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

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Clear the DTCs.

Click here

Powertrain > Engine and ECT > Clear DTCs

(e) Turn the power switch off and wait for at least 30 seconds.

(f) Turn the power switch on (IG).

(g) Turn the Techstream on.

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

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(i) Start the engine and warm it up.

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

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

(l) Read the DTCs.

Powertrain > Engine and ECT > Trouble Codes

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

END

16.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE EGR STEP POSITION)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

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

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) 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.

(f) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Primary / MAP and Throttle Idle Position.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the EGR Step Position

Data List Display
MAP
Throttle Idle Position

(g) Confirm that the Throttle Idle Position is ON and check the MAP values in the Data List while performing the Active Test.

HINT:

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

OK:

MAP 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

MAP

(Data List)

(EGR valve is fully closed)

MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

HINT:

While performing the Active Test, if the increase in the value of MAP is small, the EGR valve assembly may be a malfunctioning.
Even if the EGR valve assembly is malfunctioning, rough idling or an increase in the value of MAP may occur while performing the Active Test. However, the amount that the value of MAP increases will be smaller than normal.

GO TO STEP 18

17.	INSPECT EGR VALVE ASSEMBLY

(a) Remove the EGR valve assembly.

Click here

(b) Check if the EGR valve is stuck open.

OK:

EGR valve is tightly closed.

HINT:

Perform "Inspection After Repair" after replacing the EGR valve assembly.

Click here

REPLACE EGR VALVE ASSEMBLY

18.	CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION)

(a) Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter sub-assembly and ECM.

Click here

HINT:

Repair any problems.

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

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Clear the DTCs.

Click here

Powertrain > Engine and ECT > Clear DTCs

(e) Turn the power switch off and wait for at least 30 seconds.

(f) Turn the power switch on (IG).

(g) Turn the Techstream on.

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

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(i) Start the engine and warm it up.

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

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

(l) Read the DTCs.

Powertrain > Engine and ECT > Trouble Codes

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

END

20.	CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY - ECM)

Click here

REPAIR OR REPLACE HARNESS OR CONNECTOR

21.	REPLACE MASS AIR FLOW METER SUB-ASSEMBLY

(a) Replace the mass air flow meter sub-assembly.

Click here

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.
Perform "Inspection After Repair" after replacing the mass air flow meter sub-assembly.
Click here

22.	CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(d) Clear the DTCs.

Click here

Powertrain > Engine and ECT > Clear DTCs

(e) Turn the power switch off and wait for at least 30 seconds.

(f) Turn the power switch on (IG).

(g) Turn the Techstream on.

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

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(i) Start the engine and warm it up.

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

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

(l) Read the DTCs.

Powertrain > Engine and ECT > Trouble Codes

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

END

REPLACE ECM

23.	INSPECT EFI-MAIN NO. 2 RELAY

(a) Inspect the EFI-MAIN No. 2 relay.

Click here

REPLACE EFI-MAIN NO. 2 RELAY

24.	CHECK HARNESS AND CONNECTOR (EFI-MAIN NO. 2 RELAY - AIR FUEL RATIO SENSOR, EFI-MAIN RELAY)

(a) Remove the EFI-MAIN NO. 2 relay from the No. 1 engine room relay block and junction block assembly.

(b) Remove the EFI-MAIN relay from the No. 1 engine room relay block and junction block assembly.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
3 (EFI-MAIN NO. 2 relay) - C5-2 (+B)	Always	Below 1 Ω
1 (EFI-MAIN NO. 2 relay) - 3 (EFI-MAIN relay)	Always	Below 1 Ω
2 (EFI-MAIN NO. 2 relay) - Body ground	Always	Below 1 Ω
3 (EFI-MAIN NO. 2 relay) or C5-2 (+B) - Body ground	Always	10 kΩ or higher
1 (EFI-MAIN NO. 2 relay) or 3 (EFI-MAIN relay) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

25.	CHECK TERMINAL VOLTAGE (POWER SOURCE OF EFI-MAIN NO. 2 RELAY)

(a) Remove the EFI-MAIN NO. 2 relay from the No. 1 engine room relay block and junction block assembly.

*1	No. 1 Engine Room Relay Block and Junction Block Assembly
*2	EFI-MAIN NO. 2 Relay

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
5 (EFI-MAIN NO. 2 relay) - Body ground	Always	11 to 14 V

GO TO ECM POWER SOURCE CIRCUIT

REPAIR OR REPLACE HARNESS OR CONNECTOR (AUXILIARY BATTERY - EFI-MAIN NO. 2 RELAY)

SEE MORE:

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Oil Pressure Switch

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Lexus NX: System Too Lean (Bank 1) (P0171,P0172)

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