DTC    P0171    System Too Lean (Bank 1)
DTC    P0172    System Too Rich (Bank 1)

for Preparation Click here

DESCRIPTION

HINT:

1. 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.
   
2. If the vehicle runs out of fuel, the air fuel ratio is lean and DTC P0171 may be set. The MIL is then illuminates.
   
3. 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

CONFIRMATION DRIVING PATTERN

1. Connect the intelligent tester to the DLC3.
   
2. Turn the power switch on (IG) and turn the tester on.
   
3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation) (Click here).
   
4. Turn the power switch off and wait for 30 seconds.
   
5. Turn the power switch on (IG) and turn the tester on [A].
   
6. Put the engine in inspection mode (maintenance mode) (Click here).
   
7. 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].
   
8. With the engine warmed up, idle the engine for 2 minutes or more [C].
   
9. Drive the vehicle at between 75 and 120 km/h (47 and 75 mph) for 5 minutes or more [D].
   

   CAUTION:

   When performing the confirmation driving pattern, obey all speed limits and traffic laws.

10. Enter the following menus: Powertrain / Engine and ECT / DTC.
    
11. Read the pending DTC [E].
    

    HINT:

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

WIRING DIAGRAM

INSPECTION PROCEDURE

NOTICE:

Inspect the fuses for circuits related to this system before performing the following inspection procedure.

HINT:

1. 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 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.
   
2. 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.
   
3. 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.
   
4. Sensor 1 refers to the sensor closest to the engine assembly.
   
5. Sensor 2 refers to the sensor farthest away from the engine assembly.
   

1. Connect the intelligent tester to the DLC3.
   

2. Turn the power switch on (IG).
   

3. Turn the tester on.
   

4. Enter the following menus: Powertrain / Engine and ECT / DTC.
   

5. Read the DTCs.
   
   

   Result 

   Result	Proceed to
   DTC P0171 or P0172 is output	A
   DTC P0171 or P0172 and other DTCs are output	B

   HINT:

   If any DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.

B	GO TO DTC CHART (Click here)

A

1. Inspect the PCV hose connections (Click here).
   

   OK:

   PCV valve and hose is connected correctly and is not damaged.
   

NG	REPAIR OR REPLACE PCV HOSE

OK

1. Check the intake system for vacuum leaks (Click here).
   

   OK:

   No leaks in intake system.
   

NG	REPAIR OR REPLACE INTAKE SYSTEM

OK

1. Connect the intelligent tester to the DLC3.
   

2. Turn the power switch on (IG).
   

3. Turn the tester on.
   

4. Put the engine in inspection mode (maintenance mode) (Click here).
   

5. Start the engine.
   

6. Warm up the engine and run the engine at an engine speed of 2500 rpm for approximately 90 seconds.
   

   HINT:

   During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, warm up the engine after charging control has completed.

7. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.
   

8. 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).
   

9. 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.
   

   HINT:

   1. The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.
      
   2. 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.
      
   3. If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.
      
   
   

   Standard 

   Tester Display (Sensor)	Injection Volume	Status	Voltage
   AFS Voltage B1S1 (Air fuel ratio)	12.5%	Rich	Less than 3.1 V
   	-12.5%	Lean	Higher than 3.4 V
   O2S B1S2 (Heated oxygen)	12.5%	Rich	Higher than 0.55 V
   	-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	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 leak from exhaust system Intake system Fuel pressure Mass air flow meter sub-assembly Engine coolant temperature sensor	A
   Rich	Rich	Actual air fuel ratio rich	Fuel injector assembly leak 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

   1. Lean: During Control the Injection Volume for A/F Sensor, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently less than 0.4 V.
      
   2. Rich: During Control the Injection Volume for A/F Sensor, the AFS Voltage B1S1 is consistently less than 3.1 V, and the O2S B1S2 is consistently higher than 0.55 V.
      
   3. Lean/Rich: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the air fuel ratio sensor and the heated oxygen sensor alternates correctly.
      

   HINT:

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

B	Go to step 11

A

1. Connect the intelligent tester to the DLC3.
   

2. Turn the power switch on (IG).
   

3. Turn the tester on.
   

4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.
   

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

   Standard 

   Tester Display	Condition	Specified Condition
   Coolant Temp	Cold engine	Same as ambient air temperature
   	Warm engine	Between 75 and 100°C (167 and 212°F)

NG	REPLACE ENGINE COOLANT TEMPERATURE SENSOR (Click here)

OK

1. Connect the intelligent tester to the DLC3.
   

2. Turn the power switch on (IG).
   

3. Turn the tester on.
   

4. Put the engine in inspection mode (maintenance mode) (Click here).
   

5. Start the engine.
   

6. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / MAF, Coolant Temp and Engine Speed.
   

7. Allow the engine to idle until Coolant Temp reaches 75°C (167°F) or higher.
   

8. Read MAF with the engine speed at 2500 rpm.
   

   HINT:

   During charging control, the engine speed is set at idle. Therefore, the engine speed does not increase when depressing the accelerator pedal. In this case, read the Data List after charging control has completed.

   
   

   Standard 

   Tester Display	Condition	Specified Condition
   MAF	Park (P) has been selected A/C: off Engine Speed: 2500 rpm	Between 4.5 gm/sec. and 8.5 gm/sec.

NG	Go to step 16

OK

1. Check the fuel pressure (Click here).
   

NG	REPAIR OR REPLACE FUEL SYSTEM

OK

1. Inspect for exhaust gas leaks.
   

   OK:

   No gas leaks.
   

NG	REPAIR OR REPLACE EXHAUST SYSTEM

OK

1. Perform a spark test (Click here).
   

HINT:

1. If the result of the spark test is normal, proceed to the next step.
   
2. 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 #4 Misfire Count).
   

NEXT

1. Check the injection and volume.
   

   HINT:

   1. Refer to the fuel injector inspection procedure (Click here).
      
   2. If the fuel injector assembly malfunction, engine misfires 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 #4 Misfire Count).
      
   
   

   Result 

   Result	Proceed to
   NG	A
   OK	B

B	Go to step 15

A
REPLACE FUEL INJECTOR ASSEMBLY (Click here)

1. Inspect the air fuel ratio sensor (Click here).
   

NG	REPLACE AIR FUEL RATIO SENSOR (Click here)

OK

1. Disconnect the air fuel ratio sensor connector.
   

2. Turn the power switch on (IG).
   

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

   Standard Voltage:

   Tester Connection	Switch Condition	Specified Condition
   D24-2 (+B) - Body ground	Power switch on (IG)	11 to 14 V

   Text in Illustration 

   *a	Front view of wire harness connector (to Air Fuel Ratio Sensor)

4. Reconnect the air fuel ratio sensor connector.
   

NG	REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - EFI MAIN RELAY)

OK

1. Disconnect the air fuel ratio sensor connector.
   

2. Disconnect the ECM connector.
   

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

   Standard Resistance:

   
   

   Tester Connection	Condition	Specified Condition
   D24-1 (HA1A) - D28-18 (HA1A)	Always	Below 1 Ω
   D24-3 (A1A+) - D28-103 (A1A+)	Always	Below 1 Ω
   D24-4 (A1A-) - D28-126 (A1A-)	Always	Below 1 Ω
   D24-1 (HA1A) or D28-18 (HA1A) - Body ground	Always	10 kΩ or higher
   D24-3 (A1A+) or D28-103 (A1A+) - Body ground	Always	10 kΩ or higher
   D24-4 (A1A-) or D28-126 (A1A-) - Body ground	Always	10 kΩ or higher

4. Reconnect the air fuel ratio sensor connector.
   

5. Reconnect the ECM connector.
   

NG	REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

1. Replace the air fuel ratio sensor (Click here).
   

NEXT

1. Connect the intelligent tester to the DLC3.
   

2. Turn the power switch on (IG).
   

3. Turn the tester on.
   

4. Clear the DTCs (Click here).
   

5. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
   

6. Enter the following menus: Powertrain / Engine and ECT / DTC / Pending.
   

7. Read the pending DTCs.
   
   

   Result 

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

B	END

A

1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter sub-assembly and ECM (Click here).
   

   HINT:

   Repair any problems.

NEXT

1. Connect the intelligent tester to the DLC3.
   

2. Turn the power switch on (IG).
   

3. Turn the tester on.
   

4. Clear the DTCs (Click here).
   

5. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
   

6. Enter the following menus: Powertrain / Engine and ECT / DTC / Pending.
   

7. Read the pending DTCs.
   
   

   Result 

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

B	END

A

1. Disconnect the mass air flow meter sub-assembly connector.
   

2. Turn the power switch on (IG).
   

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

   Standard Voltage:

   Tester Connection	Switch Condition	Specified Condition
   D5-3 (+B) - Body ground	Power switch on (IG)	11 to 14 V

   Text in Illustration 

   *a	Front view of wire harness connector (to Mass Air Flow Meter Sub-assembly)

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

NG	REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

1. Replace the mass air flow meter sub-assembly (Click here).
   

   HINT:

   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 sub-assembly.

NEXT

1. Connect the intelligent tester to the DLC3.
   

2. Turn the power switch on (IG).
   

3. Turn the tester on.
   

4. Clear the DTCs (Click here).
   

5. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
   

6. Enter the following menus: Powertrain / Engine and ECT / DTC / Pending.
   

7. Read the pending DTCs.
   
   

   Result 

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

B	REPLACE ECM (Click here)

A
END