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.

If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.

DTC No.	DTC Detection Condition	Trouble Area
P0171 P0174	With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to lean side (2 trip detection logic)	Air induction system Fuel injector assembly Mass air flow meter sub-assembly Engine coolant temperature sensor Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit Air fuel ratio sensor (bank 1, 2 sensor 1) Air fuel ratio sensor heater (bank 1, 2 sensor 1) PCV valve and hose PCV hose connections ECM Wire harness or connector
P0172 P0175	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 sub-assembly Engine coolant temperature sensor Ignition system Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit Air fuel ratio sensor (bank 1, 2 sensor 1) Air fuel ratio sensor heater circuits (bank 1, 2 sensor 1) ECM Wire harness or connector

DTC No.

DTC Detection Condition

Trouble Area

P0171

P0174

With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to lean side

(2 trip detection logic)

Air induction system
Fuel injector assembly
Mass air flow meter sub-assembly
Engine coolant temperature sensor
Fuel pressure
Gas leak from exhaust system
Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit
Air fuel ratio sensor (bank 1, 2 sensor 1)
Air fuel ratio sensor heater (bank 1, 2 sensor 1)
PCV valve and hose
PCV hose connections
ECM
Wire harness or connector

P0172

P0175

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 sub-assembly
Engine coolant temperature sensor
Ignition system
Fuel pressure
Gas leak from exhaust system
Open or short in air fuel ratio sensor (bank 1, 2 sensor 1) circuit
Air fuel ratio sensor (bank 1, 2 sensor 1)
Air fuel ratio sensor heater circuits (bank 1, 2 sensor 1)
ECM
Wire harness or connector

Tech Tips

When DTC P0171 or P0174 is set, the actual air fuel ratio is on the lean side. When DTC P0172 or P0175 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 or P0174 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, 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's 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 thresholds, the ECM interprets this a fault in the fuel system and sets a DTC.

Example:

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

WIRING DIAGRAM

Refer to DTC P0102 Click here.

Refer to DTC P2195 Click here.

CONFIRMATION DRIVING PATTERN

Connect the intelligent tester to the DLC3.
Turn the ignition switch on (IG) and turn the tester on.
Clear 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 on (IG) and turn the 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 135 km/h (38 and 85 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.

INSPECTION PROCEDURE

Note

Inspect the fuses for circuits related to this system before performing the following 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 in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume.)
Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 or AFS Voltage B2S1 and O2S B1S2 or O2S B2S2) 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	Injection Volume	Status	Voltage
AFS Voltage B1S1 AFS Voltage B2S1 (Air fuel ratio sensor)	+25%	Rich	Less than 3.1 V
AFS Voltage B1S1 AFS Voltage B2S1 (Air fuel ratio sensor)	-12.5%	Lean	More than 3.4 V
O2S B1S2 O2S B2S2 (Heated oxygen)	+25%	Rich	More than 0.55 V
O2S B1S2 O2S B2S2 (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
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 / All Data / AFS Voltage B1S1 or AFS Voltage B2S1 and O2S B1S2 or O2S B2S2; then press the graph button on the Data List view.

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.
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.
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, P0172, P0174 OR P0175)

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

Read DTCs.

Result

Result	Proceed to
P0171, P0172, P0174 or P0175	A
P0171, P0172, P0174 or P0175 and other DTCs	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.
  
  OK
  
  PCV hose is connected correctly and is not damaged.
NG
REPAIR OR REPLACE PCV HOSE

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

OK

OK
PCV hose is connected correctly and is not damaged.

OK
No leak from air induction system.

PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE 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 for A/F Sensor.
Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (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 or AFS Voltage B2S1 and O2S B1S2 or O2S B2S2) 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.

Standard

Tester Display	Injection Volume	Status	Voltage
AFS Voltage B1S1 AFS Voltage B2S1 (Air fuel ratio sensor)	+25%	Rich	Less than 3.1 V
AFS Voltage B1S1 AFS Voltage B2S1 (Air fuel ratio sensor)	-12.5%	Lean	More than 3.4 V
O2S B1S2 O2S B2S2 (Heated oxygen)	+25%	Rich	More than 0.55 V
O2S B1S2 O2S B2S2 (Heated oxygen)	-12.5%	Lean	Less than 0.4 V

Result
Status AFS Voltage B1S1 AFS Voltage B2S1	Status O2S B1S2 O2S B2S2	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 Fuel injector assembly blockage Gas leak from exhaust system Air induction system Fuel pressure Mass air flow meter sub-assembly Engine coolant temperature sensor	A
Rich	Rich	Actual air fuel ratio rich	-	Fuel injector assembly blockage 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	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) 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, the AFS is consistently less than 3.1 V, and the O2S is consistently more than 0.55 V.

Lean/Rich: During Control the Injection Volume for A/F Sensor of the 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 on (IG).
Turn the tester 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 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

INSPECT MASS AIR FLOW METER SUB-ASSEMBLY
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch on (IG).
3. Turn the 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 2500 rpm.
  
  Standard
  
  Between 8 g/sec. and 19 g/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 from the exhaust manifold sub-assembly and exhaust pipe.
  
  OK
  
  No gas leak.
NG
REPAIR OR REPLACE EXHAUST SYSTEM

OK
CHECK SPARK AND IGNITION
Tech Tips
- Refer to the ignition system inspection procedure Click here.
- 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 / All Data / Cylinder #1 Misfire Count (to Cylinder #6 Misfire Count)
NG
REPAIR OR REPLACE IGNITION SYSTEM

OK
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
Tech Tips
- Refer to the fuel injector assembly inspection procedure Click here.
- If the fuel injector assemblies malfunction, engine misfire may occur. The misfire count can be read using the intelligent tester. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #6 Misfire Count).
OK
PERFORM CONFIRMATION DRIVING PATTERN Click here

NG
REPLACE FUEL INJECTOR ASSEMBLY Click here

Standard
Between 8 g/sec. and 19 g/sec. (shift lever: N; A/C: off).

OK
No gas leak.

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Text in Illustration
*1	Bank 1
*2	Bank 2
*a	Component without harness connected (Air Fuel Ratio Sensor)

Disconnect the air fuel ratio sensor connector.

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

Standard resistance

Bank 1

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

Bank 2

Tester Connection	Condition	Specified Condition
1 (HA2A) - 2 (+B)	20°C (68°F)	1.6 to 3.2 Ω
1 (HA2A) - 4 (A2A-)	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
*1	Bank 1
*2	Bank 2
*a	Front view of wire harness connector (to Air Fuel Ratio Sensor)

Disconnect the air fuel ratio sensor connector.

Turn the ignition switch on (IG).

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

Standard voltage

Bank 1

Tester Connection	Switch Condition	Specified Condition
B20-2 (+B) - Body ground	Ignition switch on (IG)	11 to 14 V

Bank 2

Tester Connection	Switch Condition	Specified Condition
B19-2 (+B) - Body ground	Ignition switch on (IG)	11 to 14 V

Reconnect the air fuel ratio sensor connector.

INSPECT ENGINE ROOM JUNCTION BLOCK ASSEMBLY (A/F 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)

Bank 1

Tester Connection	Condition	Specified Condition
B20-1 (HA1A) - B47-17 (HA1A)	Always	Below 1 Ω

Bank 2

Tester Connection	Condition	Specified Condition
B19-1 (HA2A) - B47-19 (HA2A)	Always	Below 1 Ω

Standard resistance (Check for short)

Bank 1

Tester Connection	Condition	Specified Condition
B20-1 (HA1A) or B47-17 (HA1A) - Body ground	Always	10 kΩ or higher

Bank 2

Tester Connection	Condition	Specified Condition
B19-1 (HA2A) or B47-19 (HA2A) - Body ground	Always	10 kΩ or higher

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

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 on (IG).
Turn the tester on.
Clear DTCs Click here.
Turn the ignition switch off.
Turn the ignition switch on (IG) and 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 / Pending.

Read the pending 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 harness between the mass air flow meter sub-assembly 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 on (IG).
Turn the tester on.
Clear DTCs Click here.
Turn the ignition switch off.
Turn the ignition switch on (IG) and 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 / Pending.

Read the pending 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 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 (Check for Open)

Tester Connection	Condition	Specified Condition
B10-5 (VG) - B49-14 (VG)	Always	Below 1 Ω
B10-4 (E2G) - B49-13 (E2G)	Always	Below 1 Ω

Standard Resistance (Check for Short)

Tester Connection	Condition	Specified Condition
B10-5 (VG) or B49-14 (VG) - Body ground	Always	10 kΩ or higher

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

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 step 6 indicated no problem, proceed to the next step without replacing the mass air flow meter sub-assembly.
NEXT

CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

Connect the intelligent tester to the DLC3.
Turn the ignition switch on (IG).
Turn the tester on.
Clear DTCs Click here.
Turn the ignition switch off.
Turn the ignition switch on (IG) and 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 / Pending.

Read the pending DTCs.

Result

Result	Proceed to
DTC is not output	A
DTC P0171, P0172, P0174 or P0175 is output	B

REPLACE ECM Click here

END

INSPECT ENGINE ROOM JUNCTION BLOCK ASSEMBLY (A/F RELAY)
1. Inspect the A/F relay Click here.
NG
REPLACE ENGINE ROOM JUNCTION BLOCK ASSEMBLY (A/F RELAY) Click here

OK

CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - A/F RELAY)

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

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

Standard resistance (Check for open)

Bank 1

Tester Connection	Condition	Specified Condition
B20-2 (+B) - 2A-4	Always	Below 1 Ω

Bank 2

Tester Connection	Condition	Specified Condition
B19-2 (+B) - 2A-4	Always	Below 1 Ω

Standard resistance (Check for short)

Bank 1

Tester Connection	Condition	Specified Condition
B20-2 (+B) or 2A-4 - Body ground	Always	10 kΩ or higher

Bank 2

Tester Connection	Condition	Specified Condition
B19-2 (+B) or 2A-4 - Body ground	Always	10 kΩ or higher

Reconnect the air fuel ratio sensor connector.
Reinstall the engine room junction block assembly.

REPAIR OR REPLACE HARNESS OR CONNECTOR

REPAIR OR REPLACE HARNESS OR CONNECTOR (BATTERY - A/F RELAY)