SFI SYSTEM, Diagnostic DTC:P0171, P0172, P0174, P0175

DTC Code	DTC Name
P0171	System Too Lean (Bank 1)
P0172	System Too Rich (Bank 1)
P0174	System Too Lean (Bank 2)
P0175	System Too Rich (Bank 2)

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 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 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 P0174	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).	Air induction system Fuel injector blockage Mass air flow meter assembly Engine coolant temperature sensor Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor (for Sensor 1) circuit Air fuel ratio sensor (for Sensor 1) Air fuel ratio sensor heater (for Sensor 1) No. 1 integration relay Air fuel ratio sensor heater and No. 1 integration relay circuits PCV valve and hose PCV hose connections ECM Wire harness or connector
P0172 P0175	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 assembly Engine coolant temperature sensor Ignition system Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor (for Sensor 1) circuit Air fuel ratio sensor (for Sensor 1) Air fuel ratio sensor heater (for Sensor 1) No. 1 integration relay Air fuel ratio sensor heater and No. 1 integration relay circuits ECM

DTC No.

DTC Detection Condition

Trouble Area

P0171

P0174

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).

Air induction system
Fuel injector blockage
Mass air flow meter assembly
Engine coolant temperature sensor
Fuel pressure
Gas leak from exhaust system
Open or short in air fuel ratio sensor (for Sensor 1) circuit
Air fuel ratio sensor (for Sensor 1)
Air fuel ratio sensor heater (for Sensor 1)
No. 1 integration relay
Air fuel ratio sensor heater and No. 1 integration relay circuits
PCV valve and hose
PCV hose connections
ECM
Wire harness or connector

P0172

P0175

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 assembly
Engine coolant temperature sensor
Ignition system
Fuel pressure
Gas leak from exhaust system
Open or short in air fuel ratio sensor (for Sensor 1) circuit
Air fuel ratio sensor (for Sensor 1)
Air fuel ratio sensor heater (for Sensor 1)
No. 1 integration relay
Air fuel ratio sensor heater and No. 1 integration relay circuits
ECM

Tech Tips

When DTC P0171 or P0174 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 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 or P0174 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 ECM 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:

If the average fuel trim learning value is +35% or more, or -35% or less, the ECM interprets this as a fuel system malfunction.

CONFIRMATION DRIVING PATTERN

Connect the GTS to the DLC3.
Turn the engine switch on (IG) and turn the GTS on.
Clear DTCs (even if no DTCs are stored, perform the clear DTC operation).
Turn the engine switch off and wait for at least 30 seconds.
Turn the engine switch on (IG) and turn the GTS 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 100 km/h (38 and 63 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 the pending DTCs.

Tech Tips

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

WIRING DIAGRAM

Refer to DTC P2195 Click here.

CAUTION / NOTICE / HINT

Tech Tips

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.
Bank 1 refers to the bank that includes the No. 1 cylinder*.

*: The No. 1 cylinder is the cylinder which is farthest from the transmission.
Bank 2 refers to the bank that does not include the No. 1 cylinder.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.

PROCEDURE

CHECK FOR ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175)

Connect the GTS to the DLC3.
Turn the engine switch on (IG).
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read DTCs.

Result
Result	Proceed to
P0171, P0172, P0174 or P0175 is output	A
P0171, P0172, P0174 or P0175 and other DTCs are output	B

Tech Tips

If any DTCs other than P0171, P0172, P0174 or P0175 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 hose is connected correctly and is not damaged.
NG
REPAIR OR REPLACE PCV HOSE Click here

OK
CHECK AIR INDUCTION SYSTEM
1. Check the air induction system for vacuum leaks Click here.
  
  OK
  
  No leaks in air induction system.
NG
REPAIR OR REPLACE AIR INDUCTION SYSTEM Click here

OK

OK
PCV hose is connected correctly and is not damaged.

OK
No leaks in air induction 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.
Perform the Control the Injection Volume operation with the engine idling.

Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the GTS.

Tech Tips

Change the fuel injection volume within the range of -12.5% to +12.5%. 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 air fuel ratio sensor output voltage does not change (almost no reaction) while performing the Active Test, the air fuel ratio sensor may be malfunctioning.

GTS Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 or AFS Voltage B2S1 (Air fuel ratio)	+12.5%	Rich	Below 3.1 V
AFS Voltage B1S1 or AFS Voltage B2S1 (Air fuel ratio)	-12.5%	Lean	Higher than 3.4 V
O2S B1S2 or O2S B2S2 (Heated oxygen)	+12.5%	Rich	Higher than 0.55 V
O2S B1S2 or O2S B2S2 (Heated oxygen)	-12.5%	Lean	Below 0.4 V

Result

Status of AFS Voltage B1S1 or AFS Voltage B2S1	Status of O2S B1S2 or O2S B2S2	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 leaks from exhaust system Intake system Fuel pressure Mass air flow meter assembly Engine coolant temperature sensor	A
Rich	Rich	Actual air fuel ratio rich	Fuel injector assembly leakage or blockage Gas leaks from exhaust system Ignition system Fuel pressure Mass air flow meter assembly 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 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.

Tech Tips

Refer to "Data List / Active Test" [AFS Voltage B1S1, AFS Voltage B2S1, O2S B1S2 and O2S B2S2] 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 engine switch on (IG).
Turn the GTS on.
Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.

Read Coolant Temp twice, when the engine is both cold and warmed up.

Standard
With cold engine: Same as ambient air temperature.
With warm engine: Between 75°C and 100°C (167°F and 212°F).

REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

READ VALUE USING GTS (MAF)
1. Connect the GTS to the DLC3.
2. Turn the engine switch on (IG).
3. Turn the GTS on.
4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / MAF and Coolant Temp.
5. Allow the engine to idle until Coolant Temp reaches 75°C (167°F) or higher.
6. Read MAF with the engine speed at 3000 rpm.
  
  Standard
  
  Between 18.3 gm/sec. and 25.8 gm/sec. (shift lever: N; A/C: Off).
NG
CHECK HARNESS AND CONNECTOR Click here

OK
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.
NG
REPAIR OR REPLACE EXHAUST SYSTEM

OK
CHECK FOR SPARKS AND IGNITION
1. Perform a spark test Click here.
  
  Tech Tips
  
  If the result of the spark test is normal, proceed to the next step.
NG
REPAIR OR REPLACE IGNITION SYSTEM

OK
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
1. Check the injection and volume Click here.
OK
PERFORM CONFIRMATION DRIVING PATTERN 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

Standard
Between 18.3 gm/sec. and 25.8 gm/sec. (shift lever: N; A/C: Off).

OK
No gas leaks.

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

Text in Illustration
*a	Front view of wire harness connector (to Air Fuel Ratio Sensor)
*b	Bank 1
*c	Bank 2

Disconnect the air fuel ratio sensor connector.
Turn the engine switch on (IG).

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

Standard Voltage

Tester Connection	Switch Condition	Specified Condition
C22-2 (+B) - Body ground	Engine switch on (IG)	11 to 14 V
C23-2 (+B) - Body ground	Engine switch on (IG)	11 to 14 V

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

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

for RHD
Tester Connection	Condition	Specified Condition
C22-1 (HA1A) - C46-22 (HA1A)	Always	Below 1 Ω
C22-3 (A1A+) - C46-126 (A1A+)	Always	Below 1 Ω
C22-4 (A1A-) - C46-125 (A1A-)	Always	Below 1 Ω
C23-1 (HA2A) - C46-20 (HA2A)	Always	Below 1 Ω
C23-3 (A2A+) - C46-103 (A2A+)	Always	Below 1 Ω
C23-4 (A2A-) - C46-102 (A2A-)	Always	Below 1 Ω
C22-1 (HA1A) or C46-22 (HA1A) - Body ground	Always	10 kΩ or higher
C22-3 (A1A+) or C46-126 (A1A+) - Body ground	Always	10 kΩ or higher
C22-4 (A1A-) or C46-125 (A1A-) - Body ground	Always	10 kΩ or higher
C23-1 (HA2A) or C46-20 (HA2A) - Body ground	Always	10 kΩ or higher
C23-3 (A2A+) or C46-103 (A2A+) - Body ground	Always	10 kΩ or higher
C23-4 (A2A-) or C46-102 (A2A-) - Body ground	Always	10 kΩ or higher

for LHD
Tester Connection	Condition	Specified Condition
C22-1 (HA1A) - C45-22 (HA1A)	Always	Below 1 Ω
C22-3 (A1A+) - C45-126 (A1A+)	Always	Below 1 Ω
C22-4 (A1A-) - C45-125 (A1A-)	Always	Below 1 Ω
C23-1 (HA2A) - C45-20 (HA2A)	Always	Below 1 Ω
C23-3 (A2A+) - C45-103 (A2A+)	Always	Below 1 Ω
C23-4 (A2A-) - C45-102 (A2A-)	Always	Below 1 Ω
C22-1 (HA1A) or C45-22 (HA1A) - Body ground	Always	10 kΩ or higher
C22-3 (A1A+) or C45-126 (A1A+) - Body ground	Always	10 kΩ or higher
C22-4 (A1A-) or C45-125 (A1A-) - Body ground	Always	10 kΩ or higher
C23-1 (HA2A) or C45-20 (HA2A) - Body ground	Always	10 kΩ or higher
C23-3 (A2A+) or C45-103 (A2A+) - Body ground	Always	10 kΩ or higher
C23-4 (A2A-) or C45-102 (A2A-) - 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.
NEXT

PERFORM CONFIRMATION DRIVING PATTERN

Connect the GTS to the DLC3.
Turn the engine switch on (IG).
Turn the GTS on.
Clear the DTCs Click here.
Turn the engine switch off.
Turn the engine switch on (IG) and 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, P0172, P0174 or P0175 is output	A
DTC is not output	B

END

CHECK HARNESS AND CONNECTOR
1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM Click here.
  
  Tech Tips
  
  Repair any problems.
NEXT

CHECK WHETHER DTC OUTPUT RECURS

Connect the GTS to the DLC3.
Turn the engine switch on (IG).
Turn the GTS on.
Clear the DTCs Click here.
Turn the engine switch off.
Turn the engine switch on (IG) and 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, P0172, P0174 or P0175 is output	A
DTC is not output	B

END

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

for RHD
Tester Connection	Condition	Specified Condition
C50-3 (VG) - C46-74 (VG)	Always	Below 1 Ω
C50-2 (E2G) - C46-75 (E2G)	Always	Below 1 Ω
C50-3 (VG) or C46-74 (VG) - Body ground	Always	10 kΩ or higher

for LHD
Tester Connection	Condition	Specified Condition
C50-3 (VG) - C45-74 (VG)	Always	Below 1 Ω
C50-2 (E2G) - C45-75 (E2G)	Always	Below 1 Ω
C50-3 (VG) or C45-74 (VG) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE MASS AIR FLOW METER ASSEMBLY
1. Replace the mass air flow meter 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 assembly.
NEXT

CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

Connect the GTS to the DLC3.
Turn the engine switch on (IG).
Turn the GTS on.
Clear the DTCs Click here.
Turn the engine switch off.
Turn the engine switch on (IG) and 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 is not output	A
DTC P0171, P0172, P0174 or P0175 is output	B

END

REPLACE ECM Click here

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

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
C22-2 (+B) - 1A-4	Always	Below 1 Ω
C23-2 (+B) - 1A-4	Always	Below 1 Ω
1A-3 - Body ground	Always	Below 1 Ω
C22-2 (+B) or 1A-4 - Body ground	Always	10 kΩ or higher
C23-2 (+B) or 1A-4 - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

INSPECT NO. 1 INTEGRATION RELAY (A/F)
1. Inspect the No. 1 integration relay (A/F) Click here.
OK
CHECK ECM POWER SOURCE CIRCUIT Click here

NG
REPLACE NO. 1 INTEGRATION RELAY