SFI SYSTEM, Diagnostic DTC:P0171, P0172

DTC Code	DTC Name
P0171	System Too Lean (Bank 1)
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 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 warm engine and stable air fuel ratio feedback, fuel trim considerably in error to lean side (2 trip detection logic)	Intake system Fuel injector assembly blockage Mass air flow meter sub-assembly Engine coolant temperature sensor Fuel pressure Gas leaks 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
P0172	With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to rich side (2 trip detection logic)	Fuel injector assembly leak or blockage Mass air flow meter sub-assembly Engine coolant temperature sensor Ignition system Fuel pressure Gas leaks 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

Tech Tips

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 35% or higher, or -35% or less, the ECM interprets this as a fuel system malfunction.

MONITOR STRATEGY

Required Sensors/Components

Air fuel ratio sensor

Mass air flow meter sub-assembly

Crank position sensor

Frequency of Operation

Continuous

TYPICAL ENABLING CONDITIONS

Fuel system status	Closed loop
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 higher

TYPICAL MALFUNCTION THRESHOLDS

Fuel Trim
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 GTS to the DLC3.
Turn the ignition switch to ON and turn the GTS on.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON and turn the GTS on. [A]
Start the engine and warm it up (until the engine coolant temperature 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 100 km/h (37 and 62 mph) for 5 minutes or more [D].

Note

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 the pending DTCs.

Tech Tips

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

WIRING DIAGRAM

Refer to DTC P0031 Click here.

Refer to DTC P0102 Click here.

CAUTION / NOTICE / HINT

Note

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

Tech Tips

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 GTS. Freeze frame data records the engine condition when malfunctions are detected. 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.

PROCEDURE

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

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read the DTCs.

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

Tech Tips

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

GO TO DTC CHART Click here

CHECK PCV HOSE CONNECTIONS
1. Check the PCV hose connections Click here.
  
  OK
  
  PCV valve and hose are connected correctly and are not damaged.
NG
REPAIR OR REPLACE PCV HOSE

OK
CHECK INTAKE SYSTEM
1. Check the intake system for vacuum leaks Click here.
  
  OK
  
  No leaks in intake system.
  Tech Tips
  - Perform "Inspection After Repair" after repairing or replacing the intake system Click here.
  - If a malfunction is detected while the brake pedal is being depressed, vacuum leaks in the brake booster assembly are suspected. Inspect the brake booster assembly.
NG
REPAIR OR REPLACE INTAKE SYSTEM

OK

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

OK
No leaks in intake system.

PERFORM ACTIVE TEST USING GTS (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

Connect the GTS to the DLC3.
Start the engine.
Turn the GTS 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 for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.
Perform the Control the Injection Volume for A/F Sensor 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 GTS.

Tech Tips

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 Voltage

GTS 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

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 sub-assembly Engine coolant temperature sensor EGR valve assembly	A
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	A
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, 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, 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 for A/F Sensor of the Active Test, the output voltage of the air fuel ratio sensor and heated oxygen sensor alternates correctly.

Tech Tips

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

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here

READ VALUE USING GTS (COOLANT TEMP)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.

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

Standard

GTS 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)

Tech Tips

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

REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

READ VALUE USING GTS (MAF)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / 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 3000 rpm.

Standard

GTS Display

Condition

Specified Condition

MAF

Shift lever position: N

A/C: off

Engine Speed: 3000 rpm

Between 4 gm/sec. and 10 gm/sec.

CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION) Click here

CHECK FUEL PRESSURE
1. Check the fuel pressure Click here.
NG
REPAIR OR REPLACE FUEL SYSTEM

OK
CHECK FOR EXHAUST GAS LEAK
1. Check for exhaust gas leaks.
  
  OK
  
  No gas leaks.
  
  Tech Tips
  
  Perform "Inspection After Repair" after repairing or replacing the exhaust system Click here.
NG
REPAIR OR REPLACE EXHAUST SYSTEM

OK
CHECK FOR SPARK (SPARK TEST)
1. Perform a spark test Click here.
  Tech Tips
  - 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 GTS. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).
  - Perform "Inspection After Repair" after repairing or replacing the ignition system Click here.
NEXT
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
1. Check the injection and volume.
  Tech Tips
  - Inspect the fuel injector assembly Click here.
  - If the injectors malfunction, engine misfire may occur. The misfire count can be read using the GTS. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).
  - Perform "Inspection After Repairs" after replacing the fuel injector assembly Click here.
OK
CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172) Click here

NG
REPLACE FUEL INJECTOR ASSEMBLY Click here
INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
1. Inspect the air fuel ratio sensor Click here.
NG
REPLACE AIR FUEL RATIO SENSOR Click here

OK

OK
No gas leaks.

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

Text in Illustration

*a
Front view of wire harness connector

(to Air Fuel Ratio Sensor)

Disconnect the air fuel ratio sensor connector.
Turn the ignition switch to ON.

Text in Illustration
*a	Front view of wire harness connector (to Air Fuel Ratio Sensor)

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

Standard Voltage

Tester Connection	Condition	Specified Condition
B39-2 (+B) - Body ground	Ignition switch ON	11 to 14 V

REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 INTEGRATION RELAY)

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
B39-1 (HA1A) - B23-23 (HA1A)	Always	Below 1 Ω
B39-3 (A1A+) - B23-133 (A1A+)	Always	Below 1 Ω
B39-4 (A1A-) - B23-134 (A1A-)	Always	Below 1 Ω
B39-1 (HA1A) or B23-23 (HA1A) - Body ground	Always	10 kΩ or higher
B39-3 (A1A+) or B23-133 (A1A+) - Body ground	Always	10 kΩ or higher
B39-4 (A1A-) or B23-134 (A1A-) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE AIR FUEL RATIO SENSOR
1. Replace the air fuel ratio sensor Click here.
  
  Tech Tips
  
  Perform "Inspection After Repairs" after replacing the air fuel ratio sensor Click here.
NEXT

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Clear the DTCs Click here.
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON.
Turn the GTS 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 the DTCs.

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

END

PERFORM ACTIVE TEST USING GTS (CONTROL THE EGR STEP POSITION)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or more.

Tech Tips

The A/C switch and all accessory switches should be off.
Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / All Data / MAP.

Check the engine idling condition and MAP values in the Data List while performing the Active Test.

Tech Tips

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 and idling condition change in response to EGR step position.

Standard

EGR Step Position (Active Test)

0 Steps

0 to 30 Steps

Idling condition

Steady idling

Idling changes from steady to rough idling or engine stalls

MAP

(Data List)

MAP value is 20 to 48 kPa(abs) [150 to 360 mmHg(abs)]

(EGR valve is fully closed)

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

Result
Result	Proceed to
NG	A
OK	B

Tech Tips

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.

CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION) Click here

INSPECT EGR VALVE ASSEMBLY (VISUALLY CHECK EGR VALVE)
1. Remove the EGR valve assembly Click here.
2. Check if the EGR valve is stuck open.
  
  OK
  
  EGR valve is tightly closed.
  
  Tech Tips
  
  Perform "Inspection After Repair" after replacing the EGR valve assembly Click here.
NG
REPLACE EGR VALVE ASSEMBLY Click here

OK
CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER SUB-ASSEMBLY CONNECTOR CONNECTION)
1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter sub-assembly and ECM Click here.
  
  Tech Tips
  
  Repair any problems.
NEXT

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Clear the DTCs Click here.
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON.
Turn the GTS 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 the DTCs.

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

END

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

Disconnect the mass air flow meter sub-assembly connector.
Disconnect the ECM connector.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
B72-3 (VG) - B23-91 (VG)	Always	Below 1 Ω
B72-2 (E2G) - B23-92 (E2G)	Always	Below 1 Ω
B72-3 (VG) or B23-91 (VG) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE MASS AIR FLOW METER SUB-ASSEMBLY
1. Replace the mass air flow meter sub-assembly Click here.
  Tech Tips
  - 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.
NEXT

CHECK WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

Connect the GTS to the DLC3.
Turn the ignition switch to ON.
Turn the GTS on.
Clear the DTCs Click here.
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON.
Turn the GTS 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

REPLACE ECM Click here

END