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 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	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 (Sensor 1) circuit Air fuel ratio sensor (Sensor 1) Air fuel ratio sensor heater (Sensor 1) A/F 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	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 leakage 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 (Sensor 1) circuit Air fuel ratio sensor (Sensor 1) Air fuel ratio sensor heater (Sensor 1) A/F relay Air fuel ratio sensor heater and No. 1 integration relay circuits ECM Wire harness or connector

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 ECM estimated fuel injection volumes 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 threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.

Example:

If the average fuel trim learned value is +35% or more, 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, 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 800 rpm
2. Engine load	12% or more

TYPICAL MALFUNCTION THRESHOLDS

Purge-cut	Executing
Either of following conditions 1 or 2 met	-
1. Average of short-term fuel trim and long-term fuel trim	35% or more (varies with engine coolant temperature)
2. Average of short-term fuel trim and long-term fuel trim	-35% or less (varies with engine coolant temperature)

CONFIRMATION DRIVING PATTERN

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON and turn the intelligent tester on.
Clear the 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 intelligent tester 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 / DTC [E].
Read the pending DTCs.

Tech Tips

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

WIRING DIAGRAM

Refer to DTC P2237 Click here.

INSPECTION PROCEDURE

Tech Tips

Read freeze frame data using the intelligent tester. 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.
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 OR P0172)

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

Read the DTCs.

Result
Result	Proceed to
P0171 or P0172 is output	A
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 Click here

OK
CHECK INTAKE SYSTEM
1. Check the intake system for vacuum leaks.
  
  OK
  
  No leaks in intake system.
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 (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

Connect the intelligent tester to the DLC3.
Start the engine.
Turn the intelligent tester 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 for A/F Sensor operation with the engine idling.

Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the intelligent tester.

Tech Tips

Change the fuel injection volume within the range of -12.5% to +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.

Intelligent Tester 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 0.59 V
O2S B1S2 (Heated oxygen)	-12.5%	Lean	Below 0.21 V

Result
Status of AFS Voltage B1S1	Status of 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 leaks 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 leakage or blockage Gas leaks 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 the Control the Injection Volume for A/F Sensor 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 0.21 V.

Rich: During the Control the Injection Volume for A/F Sensor Active Test, the AFS Voltage is consistently below 3.1 V, and the O2S is consistently higher than 0.59 V.

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

Tech Tips

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

Click here

READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the intelligent tester 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 INTELLIGENT TESTER (MAF)
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the intelligent tester 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 6 gm/sec and 18 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. Inspect the fuel injector assembly (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 6 gm/sec and 18 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)

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
D33-2 (+B) - Body ground	Ignition switch ON	11 to 14 V

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

Tester Connection	Condition	Specified Condition
D33-1 (HA1A) - D97-104 (HA1A)	Always	Below 1 Ω
D33-1 (HA1A) or D97-104 (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.
NEXT

PERFORM CONFIRMATION DRIVING PATTERN

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

Result
Result	Proceed to
DTC P0171 or P0172 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 intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the intelligent tester on.
Clear the DTCs Click here.
Turn the ignition switch off and wait for at least 30 seconds.
Turn the ignition switch to ON and turn the intelligent 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 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 - 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
A3-3 (VG) - D97-69 (VG)	Always	Below 1 Ω
A3-2 (E2G) - D97-92 (E2G)	Always	Below 1 Ω
A3-3 (VG) or D97-69 (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.
NEXT

CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

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

Result
Result	Proceed to
DTC is not output	A
DTC P0171 or P0172 is 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 No. 1 engine room relay block.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
10B-8 - D33-2 (+B)	Always	Below 1 Ω
10A-8 - 10B-6	Always	Below 1 Ω
10B-7 - Body ground	Always	Below 1 Ω
10B-8 or D33-2 (+B) - Body ground	Always	10 kΩ or higher
10A-8 or 10B-6 - 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.
NG
REPLACE NO. 1 INTEGRATION RELAY

OK

CHECK ECM POWER SOURCE CIRCUIT Click here