DTC P0171: System Too Lean (Bank 1); DTC P0172: System Too Rich (Bank 1): Procedure

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
5. Read DTCs.
   RESULT
   
   

   Result	Proceed to
   P0171 or P0172	A
   P0171 or P0172 and other DTCs	B

   HINT: 

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

B → See step   22 

A: Go to next step 

1. Check the PCV hose connections. Refer to COMPONENTS .

   OK

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

NG → REPAIR OR REPLACE PCV HOSE 

OK: Go to next step 

1. Check the intake system for vacuum leak. Refer to ON-VEHICLE INSPECTION - Step 1 .

   OK

   No leak from intake system.

NG → REPAIR OR REPLACE INTAKE SYSTEM 

OK: Go to next step 

1. Connect the Techstream to the DLC3.
2. Start the engine.
3. Turn the Techstream on.
4. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
5. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
6. Change the fuel injection volume using the Techstream and monitor the voltage output of the air fuel ratio and heated oxygen sensors displayed on the Techstream.

   HINT: 

   • The Control the Injection Volume for A/F Sensor operation lowers or increases the fuel injection volume by 12.5%.
   • The air fuel ratio sensor is displayed as AFS Voltage B1S1, and the heated oxygen sensor is displayed as O2S B1S2, on the Techstream.
   • 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.

   Standard

   Techstream Display (Sensor)	Injection Volume	Status	Voltage
   AFS Voltage B1S1 (Air fuel ratio)	12.5%	Rich	Less than 3.1
   	-12.5%	Lean	More than 3.4
   O2S B1S2 (Heated oxygen)	12.5%	Rich	More than 0.55
   	-12.5%	Lean	Less than 0.4

   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 blockage Gas leak 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 blockage or blockage Gas leak from exhaust system Ignition system Fuel pressure Mass air flow meter 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 Active Test, the air fuel ratio sensor output voltage (AFS Voltage B1S1) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S B1S2) is consistently less than 0.4 V.

   Rich: During Control the Injection Volume for A/F Sensor Active Test, the AFS Voltage B1S1 is consistently less than 3.1 V, and the O2S B1S2 is consistently more than 0.55 V.

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

   HINT: 

   Refer to "Data List / Active Test" [AFS Voltage B1S1 and O2S B1S2]. Refer to DATA LIST / ACTIVE TEST .

B → See step   11 

A: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream 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

   Techstream 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 → See step   23 

OK: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Enter the following menus: Powertrain / Engine and ECT / Data List / MAF, Coolant Temp and Engine Speed.
5. Read MAF with the engine speed at 2500 rpm.

   Standard

   Techstream Display	Condition	Specified Condition
   MAF	Shift lever position: N A/C: Off Engine Speed: 2500 rpm	Between 2.0 gm/sec. and 7.0 gm/sec

NG → See step   16 

OK: Go to next step 

1. Check the fuel pressure. Refer to ON-VEHICLE INSPECTION - Step 2 .

NG → REPAIR OR REPLACE FUEL SYSTEM 

OK: Go to next step 

1. Check for exhaust gas leak.

   OK

   No gas leak.

NG → REPAIR OR REPLACE EXHAUST GAS LEAK POINT 

OK: Go to next step 

1. Perform a spark test. Refer to ON-VEHICLE INSPECTION .

   HINT: 

   If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using the Techstream. 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: Go to next step 

1. Check the injection and volume. Refer to INSPECTION .

   HINT: 

   If the injectors malfunction, engine misfire may occur. The misfire count can be read using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).

OK → See step   15 

NG → See step   24 

NG → See step   25 

OK: Go to next step 

NG → See step   21 

OK: Go to next step 

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Replace the air fuel ratio sensor. Refer to REMOVAL .

NEXT: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Clear DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off and wait for at least 30 seconds.
6. Turn the ignition switch to ON.
7. Turn the Techstream on.
8. Start the engine and warm it up.
9. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
10. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
11. Read the pending DTCs.
    RESULT
    
    

    Result	Proceed to
    P0171 or P0172	A
    No output	B

B → END 

A: Go to next step 

1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM. Refer to ELECTRONIC CIRCUIT INSPECTION PROCEDURE .

   HINT: 

   Repair any problems.

NEXT: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Clear DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off and wait for at least 30 seconds.
6. Turn the ignition switch to ON.
7. Turn the Techstream on.
8. Start the engine and warm it up.
9. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
10. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
11. Read the pending DTCs.
    RESULT
    
    

    Result	Proceed to
    P0171 or P0172	A
    No output	B

B → END 

A: Go to next step 

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Replace the mass air flow meter. Refer to REMOVAL .

   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.

NEXT: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON.
3. Turn the Techstream on.
4. Clear DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off and wait for at least 30 seconds.
6. Turn the ignition switch to ON.
7. Turn the Techstream on.
8. Start the engine and warm it up.
9. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
10. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
11. Read the pending DTCs.
    RESULT
    
    

    Result	Proceed to
    No output	A
    P0171 or P0172	B

B → See step   26 

A → END 

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK → See step   27