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 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.
   
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

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT:

Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor 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.

1. Connect the intelligent tester to the DLC3.
   
2. Turn the power switch on (IG) and turn the tester on.
   
3. Put the engine in inspection mode (Click here).
   
4. Start the engine.
   
5. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
   
6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
   
7. Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
   
8. Monitor the voltage outputs of the air fuel ratio and heated oxygen sensors (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 25%.
      
   2. Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
      
   
   

   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

   NOTICE:

   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 Exhaust gas leaks
   4			Fuel pressure Exhaust gas leaks (Air fuel ratio extremely lean or rich)

1. 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.
   
2. To display the graph, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / A/F Control System / AFS Voltage B1S1 and O2S B1S2.
   

   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.
      

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 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) and turn the tester on.
   

3. Put the engine in inspection mode (Click here).
   

4. Start the engine.
   

5. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
   

6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
   

7. 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).
   

8. Monitor the voltage outputs of the air fuel ratio sensor and the heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the intelligent 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 25%.
      
   2. Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
      
   3. 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
   	-12.5%	Lean	More than 3.4 V
   O2S B1S2 (heated oxygen)	+25%	Rich	More 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	Misfire	Suspected Trouble Area	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	-	C
   Lean	Lean	Actual air fuel ratio lean	May occur	PCV valve and hose PCV hose connections Fuel injector assembly blockage Gas leaks 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 leakage or blockage Gas leaks from exhaust system Ignition system Fuel pressure Mass air flow meter sub-assembly Engine coolant temperature sensor
   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

   Lean: During Control the Injection Volume for A/F Sensor, the air fuel ratio sensor output voltage (AFS Voltage) 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 Voltage 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.
   

B	Go to step 11
C	Go to step 15

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 / Coolant Temp.
   

5. 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).
   

NG	REPLACE ENGINE COOLANT TEMPERATURE SENSOR (Click here)

OK

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

NG	REPLACE MASS AIR FLOW METER SUB-ASSEMBLY (Click here)

OK

1. Check the fuel pressure (Click here).
   

NG	REPAIR OR REPLACE FUEL SYSTEM

OK

1. Inspect for exhaust gas leaks from the exhaust manifold sub-assembly and exhaust pipes.
   

OK:

No gas leaks.

NG	REPAIR OR REPLACE EXHAUST SYSTEM

OK

HINT:

1. Refer to the ignition system inspection procedure (Click here).
   
2. If the spark plugs or ignition system malfunctions, engine misfires 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)
   

NG	REPAIR OR REPLACE IGNITION SYSTEM

OK

HINT:

1. Refer to the fuel injector inspection procedure (Click here).
   
2. If the injectors 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 / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).
   

Result:

Result	Proceed to
NG	A
OK	B

B	Go to step 16

A
REPLACE FUEL INJECTOR ASSEMBLY (Click here)

1. Disconnect the air fuel ratio sensor connector.
   

2. 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

   Text in Illustration 

   *1	Component without harness connected (to Air Fuel Ratio Sensor)

3. Reconnect the air fuel ratio sensor connector.
   

NG	REPLACE AIR FUEL RATIO SENSOR NO.2 (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 

   *1	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 (Check for Open):

   
   

   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

   
   

   Standard Resistance (Check for Short):

   
   

   Tester Connection	Condition	Specified Condition
   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

   
   

   Text in Illustration 

   *1

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

   *2

   Front view of wire harness connector (to ECM)

4. Reconnect the air fuel ratio sensor connector.
   

5. Reconnect the ECM connector.
   

NG	REPAIR OR REPLACE HARNESS OR CONNECTOR (AIR FUEL RATIO SENSOR - ECM)

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. Turn the power switch off and wait for 30 seconds.
   

6. Turn the power switch on (IG) and turn the tester on.
   

7. Put the engine in inspection mode (Click here).
   

8. Start the power and warm it up.
   

9. With the engine warmed up, idle the engine for 2 minutes or more.
   

10. Drive the vehicle at between 75 and 120 km/h (45 and 75 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes or more.
    

11. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
    

12. Input the DTC: P0171, P0172.
    

13. Check the DTC judgment result.
    
    

    Result:

    
    

    Result	Proceed to
    ABNORMAL (DTC P0171 or P0172 is output)	A
    NORMAL (DTC is not output)	B

B	END

A

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 (Click here).
   

5. Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or more.
   

   HINT:

   The A/C switch and all accessory switches should be off.

6. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.
   

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

   HINT:

   1. Do not leave the EGR valve open for 10 seconds or more during the Active Test.
      
   2. Be sure to return the EGR valve to step 0 when the Active Test is completed.
      
   3. Do not open the EGR valve 30 steps or more during the Active Test.
      

   OK:

   MAP and idling condition change in response to EGR step position when Throttle Idle Position is ON in Data List.
   

   
   

   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

   HINT:

   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

B	Go to step 18

A

1. Remove the EGR valve assembly (Click here).
   

2. Check if the EGR valve is stuck open.
   

   OK:

   EGR valve is tightly closed.
   

3. Reinstall the EGR valve assembly (Click here).
   

NG	REPLACE EGR VALVE ASSEMBLY (Click here)

OK

1. Replace the ECM (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 DTC (Click here).
   

5. Turn the power switch off and wait for 30 seconds.
   

6. Turn the power switch on (IG) and turn the tester on.
   

7. Put the engine in inspection mode (Click here).
   

8. Start the engine and warm it up.
   

9. With the engine warmed up, idle the engine for 2 minutes or more.
   

10. Drive the vehicle at between 75 and 120 km/h (45 and 75 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes or more.
    

11. Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
    

12. Input the DTCs: P0171, P0172.
    

13. Check the DTCs judgment result.
    

NEXT
END