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 time. The fuel trim consists of both the short-term and long-term fuel trim.

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	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 blockage Mass air flow meter Engine coolant temperature sensor Fuel pressure Gas leaks from exhaust system Open or short in air fuel ratio sensor (bank 1 sensor 1) circuit Air fuel ratio sensor (bank 1 sensor 1) Air fuel ratio sensor (bank 1 sensor 1) heater 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 leak or blockage Mass air flow meter Engine coolant temperature sensor Ignition system Fuel pressure Gas leaks from exhaust system Open or short in air fuel ratio sensor (bank 1 sensor 1) circuit Air fuel ratio sensor (bank 1 sensor 1) Air fuel ratio sensor (bank 1 sensor 1) heater EGR valve assembly Wire harness or connector ECM

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 blockage
Mass air flow meter
Engine coolant temperature sensor
Fuel pressure
Gas leaks from exhaust system
Open or short in air fuel ratio sensor (bank 1 sensor 1) circuit
Air fuel ratio sensor (bank 1 sensor 1)
Air fuel ratio sensor (bank 1 sensor 1) heater
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 leak or blockage
Mass air flow meter
Engine coolant temperature sensor
Ignition system
Fuel pressure
Gas leaks from exhaust system
Open or short in air fuel ratio sensor (bank 1 sensor 1) circuit
Air fuel ratio sensor (bank 1 sensor 1)
Air fuel ratio sensor (bank 1 sensor 1) heater
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 more than 75°C [167°F]), the system is functioning normally.

MONITOR DESCRIPTION

Under closed-loop fuel control, a fuel injection volume that deviates from that estimated by the ECM causes 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 value. Deviations from the ECM's estimated fuel injection volume also affects 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 a malfunction threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example:

When the average fuel trim learning value is more than +40% or less than -40%, the ECM interprets this as a fuel system malfunction.

MONITOR STRATEGY

Required Sensors/Components	Air fuel ratio sensor, Mass air flow meter, Crankshaft position sensor
Frequency of Operation	Continuous

TYPICAL ENABLING CONDITIONS

Fuel system status	Closed loop
Battery voltage	11 V or higher
Either of following conditions 1 or 2 met	-
1. Engine speed	Less than 1100 rpm
2. Engine load	10% or more

TYPICAL MALFUNCTION THRESHOLDS

Purge-cut	Executing
Either of following conditions 1 or 2 met	-
1. Average between short-term fuel trim and long-term fuel trim	40% or more (varies with engine coolant temperature)
2. Average between short-term fuel trim and long-term fuel trim	-40% or less (varies with engine coolant temperature)

CONFIRMATION DRIVING PATTERN

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Clear DTCs Click here.
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON and turn the tester 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 between 60 and 100 km/h (37 and 63 mph) and at an engine speed 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 / DTC. [E]
Read pending DTCs.
Tech Tips
- If a pending DTC is output, the system is malfunctioning.
- If no pending DTC is output, the system is normal.

WIRING DIAGRAM

Refer to DTC P0031 Click here.

Refer to DTC P0102 Click here.

CAUTION / NOTICE / HINT

Tech Tips

Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions 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.
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 ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Enter the following menus: Powertrain / Engine and ECT / DTC.

Read 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 hose is connected correctly and is 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 Repairs" after repairing or replacing the intake system Click here.
NG
REPAIR OR REPLACE INTAKE SYSTEM

OK

OK
PCV hose is connected correctly and is not damaged.

OK
No leaks in intake system.

PERFORM ACTIVE TEST USING INTELLIGENT TESTER (INJECTION VOLUME)

Connect the intelligent tester to the DLC3.
Start the engine.
Turn the tester on.
Warm up 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 tester.

Tech Tips

Change the fuel injection volume within the range of -12% to +12%. The injection volume can be changed in fine gradations.
Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
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

Tester 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 Injector blockage Gas leak from exhaust system Intake system Fuel pressure Mass air flow meter Manifold absolute pressure sensor Engine coolant temperature sensor EGR valve assembly
Rich	Rich	Actual air fuel ratio rich	Injector blockage Gas leak from exhaust system Ignition system Fuel pressure Mass air flow meter Manifold absolute pressure sensor 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 the Control the Injection Volume Active Test, the air fuel ratio sensor output voltage (AFS) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.

Rich: During Control the Injection Volume of the Active Test, the AFS Voltage B1S1 is consistently less than 3.1 V, and the O2S B1S1 is consistently more than 0.55 V.

Lean/Rich: During the Control the Injection Volume Active Test, the output voltage of the heated oxygen sensor alternates correctly.

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) Click here

READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester 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 value
With cold engine:
Same as ambient air temperature.
With warm engine:
75 to 100°C (167 to 212°F).

Tech Tips

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

REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

READ VALUE USING INTELLIGENT TESTER (MAF)
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the tester on.
4. Enter the following menus: Powertrain / Engine and ECT / Data List / 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 3000 rpm.
  
  Standard
  
  Between 5.4 gm/sec. and 9.6 gm/sec. (shift lever: neutral; 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.
  
  Tech Tips
  
  Perform "Inspection After Repairs" after repairing or replacing the exhaust system Click here.
NG
REPAIR OR REPLACE EXHAUST SYSTEM

OK
CHECK SPARK 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.
  - If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using the intelligent tester. Enter the following menus: Powertrain / Engine and ECT / Data List / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).
  - Perform "Inspection After Repairs" after repairing or replacing the ignition system Click here.
NEXT
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION VOLUME)
1. Inspect the fuel injector assembly Click here.
  
  Tech Tips
  
  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

Standard
Between 5.4 gm/sec. and 9.6 gm/sec. (shift lever: neutral; A/C: off).

OK
No gas leaks.

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Text in Illustration

*a
Component without harness connected

(Air Fuel Ratio Sensor)

Disconnect the air fuel ratio sensor connector.

Text in Illustration
*a	Component without harness connected (Air Fuel Ratio Sensor)

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

Standard Resistance

Tester Connection	Condition	Specified Condition
1 (HA1A) - 2 (+B)	20°C (68°F)	1.6 to 3.2 Ω
1 (HA1A) - 4 (A1A-)	Always	10 kΩ or higher

Tech Tips

Perform "Inspection After Repairs" after replacing the air fuel ratio sensor Click here.

REPLACE AIR FUEL RATIO SENSOR Click here

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	Switch Condition	Specified Condition
B39-2 (+B) - Body ground	Ignition switch ON	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 LHD
Tester Connection	Condition	Specified Condition
B39-1 (HA1A) - B22-23 (HA1A)	Always	Below 1 Ω
B39-1 (HA1A) or B22-23 (HA1A) - Body ground	Always	10 kΩ or higher

for RHD
Tester Connection	Condition	Specified Condition
B39-1 (HA1A) - B23-23 (HA1A)	Always	Below 1 Ω
B39-1 (HA1A) or B23-23 (HA1A) - 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 intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Clear the DTCs Click here.
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch off.
Turn the ignition switch to ON.
Turn the tester 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 / DTC.

Read DTCs.

Result
Result	Proceed to
DTC P0171 or P0172	A
No DTCs output (No pending DTCs output)	B

END

PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION)

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester 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.

Confirm that the Throttle Idle Position is ON and check the engine idling condition and MAP values in the Data List while performing the Active Test.

MAP and idling condition change in response to EGR step position.

EGR Step Position (Active Test)

0 Steps

0 to 30 Steps

Idling condition

Steady idling

Idling changes from steady to rough idling

MAP

(Data List)

MAP value is 20 to 48 kPa

(150 to 360 mmHg)

(EGR valve is fully closed)

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

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.
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.

Result
Result	Proceed to
Outside of standard range	A
Within standard range	B

CHECK HARNESS AND CONNECTOR 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 Repairs" after replacing the EGR valve assembly Click here.
NG
REPLACE EGR VALVE ASSEMBLY Click here

OK
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 (DTC P0171 OR P0172)

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

Read DTCs.

Result
Result	Proceed to
DTC P0171 or P0172	A
No DTCs output (No pending DTCs 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 LHD
Tester Connection	Condition	Specified Condition
B73-5 (VG) - B22-91 (VG)	Always	Below 1 Ω
B73-4 (E2G) - B22-92 (E2G)	Always	Below 1 Ω
B73-5 (VG) or B22-91 (VG) - Body ground	Always	10 kΩ or higher

for RHD
Tester Connection	Condition	Specified Condition
B73-5 (VG) - B23-91 (VG)	Always	Below 1 Ω
B73-4 (E2G) - B23-92 (E2G)	Always	Below 1 Ω
B73-5 (VG) or B23-91 (VG) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE MASS AIR FLOW METER
1. Replace the mass air flow meter 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.
  - Perform "Inspection After Repairs" after replacing the mass air flow meter Click here.
NEXT

CHECK WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

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

Read DTCs.

Result
Result	Proceed to
DTC P0171 or P0172	A
No DTCs output (No pending DTCs output)	B

REPLACE ECM Click here

END

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
B39-2 (+B) - 1E-4	Always	Below 1 Ω
B39-2 (+B) or 1E-4 - Body ground	Always	10 kΩ or higher

CHECK ECM POWER SOURCE CIRCUIT Click here

REPAIR OR REPLACE HARNESS OR CONNECTOR