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 assembly Mass air flow meter Manifold absolute pressure sensor 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 heater (bank 1 sensor 1) Air fuel ratio sensor heater (bank 1 sensor 1) circuit PCV valve and hose PCV hose connections EGR valve assembly 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 Mass air flow meter Manifold absolute pressure sensor 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 heater (bank 1 sensor 1) Air fuel ratio sensor heater (bank 1 sensor 1) circuit EGR valve assembly 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 assembly
Mass air flow meter
Manifold absolute pressure sensor
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 heater (bank 1 sensor 1)
Air fuel ratio sensor heater (bank 1 sensor 1) circuit
PCV valve and hose
PCV hose connections
EGR valve assembly
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
Mass air flow meter
Manifold absolute pressure sensor
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 heater (bank 1 sensor 1)
Air fuel ratio sensor heater (bank 1 sensor 1) circuit
EGR valve assembly
ECM

Tech Tips

When DTC P0171 is set, the actual air fuel ratio is on the lean side. When DTC P0172 is set, 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 set. 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 sets a DTC.

Example:

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

CONFIRMATION DRIVING PATTERN

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 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 120 km/h (38 and 75 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes. [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 DTC.

Tech Tips

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

WIRING DIAGRAM

Refer to DTC P0136 Click here.

Refer to DTC P0102 for the mass air flow meter circuit Click here.

INSPECTION PROCEDURE

Tech Tips

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor function can help to determine whether the air fuel ratio sensor, heated oxygen sensor and other potential trouble areas are malfunctioning.

The following instructions describe how to conduct the Control the Injection Volume for A/F Sensor operation using the intelligent tester.

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 for A/F Sensor.
Perform the Active Test 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 and heated oxygen sensors (AFS Voltage B1 S1 and O2S B1 S2) displayed on the tester.

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 25%.
Each sensor reacts in accordance with increases and decreases in the fuel injection volume.

Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1 S1 (Air fuel ratio)	+25%	Rich	Less than 3.1 V
AFS Voltage B1 S1 (Air fuel ratio)	-12.5%	Lean	More than 3.4 V
O2S B1 S2 (Heated oxygen)	+25%	Rich	More than 0.55 V
O2S B1 S2 (Heated oxygen)	-12.5%	Lean	Less than 0.4 V

Note

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.

Case	Air Fuel Ratio Sensor (Sensor 1) Output Voltage	Heated Oxygen Sensor (Sensor 2) Output Voltage	Main Suspected Trouble Area
1			-
2			Air fuel ratio sensor Air fuel ratio sensor heater Air fuel ratio sensor circuit
3			Heated oxygen sensor Heated oxygen sensor heater Heated oxygen sensor circuit Gas leakage from exhaust system
4			Fuel pressure Gas leakage from exhaust system (Air fuel ratio extremely lean or rich)

Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the air fuel ratio and heated oxygen sensors.
To display the graph, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / AFS Voltage B1S1 and O2S B1S2; then press the view button on the Data List screen.

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 intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was moving or stationary, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
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 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 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 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.
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 (AIR FUEL RATIO CONTROL)

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 for A/F Sensor.
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 tester.

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 25%.
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.

Standard

Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 (air fuel ratio)	+25%	Rich	Less than 3.1 V
AFS Voltage B1S1 (air fuel ratio)	-12.5%	Lean	More than 3.4 V
O2S B1S2 (heated oxygen)	+25%	Rich	More than 0.55 V
O2S B1S2 (heated oxygen)	-12.5%	Lean	Less than 0.4 V

Result
Status AFS Voltage B1S1	Status O2S B1S2	Air Fuel Ratio Condition and Air Fuel Ratio Sensor Condition	Misfire	Suspected Trouble Area	Proceed to
Lean/Rich	Lean/Rich	Normal	-	-	A
Lean	Lean	Actual air fuel ratio lean	May occur	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
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	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) 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 for A/F Sensor 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 for A/F Sensor 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:
80 to 100°C (176 to 212°F).

REPLACE ENGINE COOLANT TEMPERATURE SENSOR Click here

READ VALUE USING INTELLIGENT TESTER (MAP)
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch ON and turn the intelligent tester on.
3. Enter the following menus: Powertrain / Engine and ECT / Data List / MAP.
4. Read the MAP value.
  
  OK
  
  Same value as the actual atmospheric pressure.
  Tech Tips
  - Standard atmospheric pressure is 101 kPa (758 mmHg). For every 100 m increase in altitude, pressure drops by 1 kPa (7.50 mmHg).
    
    Varies by weather (high atmospheric pressure, low atmospheric pressure).
  - Also, check "Atmospheric Pressure" in the Data List.
NG
REPLACE MANIFOLD ABSOLUTE PRESSURE SENSOR Click here

OK
READ VALUE USING INTELLIGENT TESTER (MAF)
1. Connect the intelligent tester to the DLC3.
2. Start the engine.
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 at 2500 rpm.
  
  Standard
  
  Between 2.3 gm/sec and 6.0 gm/sec (shift lever: neutral; A/C: Off).
NG
CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER CONNECTOR CONNECTION) 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 from the exhaust manifold sub-assembly and exhaust pipes.
  
  OK
  
  No gas leaks.
NG
REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT

OK
CHECK FOR SPARK AND IGNITION
1. Check the ignition system Click here.
NG
REPAIR OR REPLACE IGNITION SYSTEM Click here

OK
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION VOLUME)
1. Inspect the fuel injection volume Click here.
OK
CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172) Click here

NG
REPLACE FUEL INJECTOR ASSEMBLY Click here

OK
Same value as the actual atmospheric pressure.

Standard
Between 2.3 gm/sec and 6.0 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)	1.8 to 3.4 Ω
1 (HA1A) - 4 (A1A-)	Always	10 kΩ or higher

Reconnect the air fuel ratio sensor connector.

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
B34-2 (+B) - Body ground	Ignition switch ON	11 to 14 V

Reconnect the air fuel ratio sensor connector.

CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - 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 (Check for Open)

Tester Connection	Condition	Specified Condition
C34-1 (HA1A) - B8-104 (HA1A)	Always	Below 1 Ω
C34-3 (A1A+) - B8-103 (A1A+)	Always	Below 1 Ω
C34-4 (A1A-) - B8-126 (A1A-)	Always	Below 1 Ω

Standard Resistance (Check for Short)

Tester Connection	Condition	Specified Condition
C34-1 (HA1A) or B8-104 (HA1A) - Body ground	Always	10 kΩ or higher
C34-3 (A1A+) or B8-103 (A1A+) - Body ground	Always	10 kΩ or higher
C34-4 (A1A-) or B8-126 (A1A-) - Body ground	Always	10 kΩ or higher

Reconnect the air fuel ratio sensor connector.
Reconnect the ECM connector.

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPLACE AIR FUEL RATIO SENSOR
1. Replace the air fuel ratio sensor Click here.
NEXT

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

Perform the confirmation driving pattern.

Tech Tips

Refer to the CONFIRMATION DRIVING PATTERN.

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

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

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.

Check the MAP and Engine Speed in Date List at the idling condition while performing 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

MAP

(Data List)

MAP value is 20 to 40 kPa (150 to 300 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 Active Test is completed.

Result
Result	Proceed to
NG	A
OK	B

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

INSPECT EGR VALVE ASSEMBLY
1. Remove the EGR valve assembly Click here.
2. Check if the EGR valve is stuck open.
  
  OK
  
  EGR valve is tightly closed (It is not stuck open).
3. Reinstall the EGR valve assembly Click here.
NG
REPLACE EGR VALVE ASSEMBLY Click here

OK
CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER CONNECTOR CONNECTION)
1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM Click here.
NEXT

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

Perform the confirmation driving pattern.

Tech Tips

Refer to the CONFIRMATION DRIVING PATTERN.

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 (Check for Open)

Tester Connection	Condition	Specified Condition
B53-5 (VG) - B8-69 (VG)	Always	Below 1 Ω
B53-4 (E2G) - B8-92 (E2G)	Always	Below 1 Ω

Standard Resistance (Check for Short)

Tester Connection	Condition	Specified Condition
B53-5 (VG) or B8-69 (VG) - Body ground	Always	10 kΩ or higher

Reconnect the mass air flow meter connector.
Reconnect the ECM connector.

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 7 indicated no problem, proceed to the next step without replacing the mass air flow meter.
NEXT

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

Perform the confirmation driving pattern.

Tech Tips

Refer to the CONFIRMATION DRIVING PATTERN.

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

REPLACE ECM Click here

END

CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY)

Disconnect the air fuel ratio sensor connector.
Remove the integration relay from the engine room relay block.

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

Standard Resistance (Check for Open)

Tester Connection	Condition	Specified Condition
B34-2 (+B) - 1E-1	Always	Below 1 Ω

Standard Resistance (Check for Short)

Tester Connection	Condition	Specified Condition
B34-2 (+B) or 1E-1 - Body ground	Always	10 kΩ or higher

Reconnect the air fuel ratio sensor connector.
Reinstall the integration relay.

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPAIR OR REPLACE ECM POWER SOURCE CIRCUIT Click here