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 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 → See step   22 

A: Go to next step 

1. Inspect the PCV hose connections. Refer to ON-VEHICLE INSPECTION - Step 1 .

   OK

   PCV hose is connected correctly and is not damaged.

NG → REPAIR OR REPLACE PCV HOSE 

OK: Go to next step 

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

   OK

   No leaks in 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 and run 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 / All Data / AFS Voltage B1S1 and O2S B1S2.
6. Perform the Control the Injection Volume operation with the engine idling.
7. Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the Techstream.

   HINT: 

   • Change the fuel injection volume within the range of -12% to +12%. The injection volume can be changed in fine gradations.
   • 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 there is almost no response from the air fuel ratio sensor, a malfunction of the air fuel ratio sensor is suspected.

   Techstream Display (Sensor)	Injection Volume	Status	Voltage
   AFS Voltage B1S1 (Air fuel ratio)	+12%	Rich	Below 3.1 V
   	-12%	Lean	Higher than 3.4 V
   O2S B1S2 (Heated oxygen)	+12%	Rich	Higher than 0.55 V
   	-12%	Lean	Below 0.4 V

   RESULT
   
   

   Status of AFS Voltage B1S1	Status of 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 leaks from exhaust system Intake system Fuel pressure Mass air flow meter 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 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 the Control the Injection Volume Active Test, the air fuel ratio sensor output voltage (AFS Voltage) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.

   Rich: During the Control the Injection Volume Active Test, the AFS Voltage is consistently below 3.1 V, and the O2S is consistently higher than 0.55 V.

   Lean/Rich: During the Control the Injection Volume Active Test, the output voltage of the 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 Coolant Temp twice, when the engine is both cold and warmed up.

   Standard value

   With cold engine: Same as ambient air temperature.

   With 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 / All Data / MAF, Coolant Temp and Engine Speed.
5. Allow the engine to idle until Coolant Temp reaches 75°C (167°F) or higher.
6. Read MAF with the engine speed at 3000 rpm.

   Standard

   Between 5 gm/s and 10 gm/s (Shift lever: Neutral; A/C: Off).

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 leaks.

   OK

   No gas leaks.

NG → REPAIR OR REPLACE EXHAUST SYSTEM 

OK: Go to next step 

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

   HINT: 

   • If the result of the spark test is normal, proceed to the next step.
   • 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 / Gas Misfire / Cylinder #1 Misfire Count (to Cylinder #4 Misfire Count).

NEXT: Go to next step 

1. Check the inspection and volume.

   HINT: 

   • Refer to the fuel injector assembly inspection procedure. Refer to INSPECTION .
   • If the fuel injector assemblies malfunction, engine misfire may occur. The misfire count can be read using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Gas Misfire / 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 (AIR FUEL RATIO SENSOR - ECM) 

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 and turn the Techstream on.
3. Clear the DTCs. Refer to DTC CHECK / CLEAR .
4. Turn the ignition switch off.
5. Turn the ignition switch to ON and turn the Techstream on.
6. Start the engine and warm it up.
7. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
8. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
9. Read the DTCs.

   Result

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

B → END 

A: Go to next step 

1. Check the connection and terminal contact pressure of connectors and wire harness 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 the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off.
6. Turn the ignition switch to ON and turn the Techstream on.
7. Start the engine and warm it up.
8. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
10. Read the DTCs.

    Result

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

B → END 

A: Go to next step 

1. Disconnect the mass air flow meter 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
   B2-5 (VG) - B29-69 (VG)	Always	Below 1 Ω
   B2-4 (E2G) - B29-92 (E2G)	Always	Below 1 Ω

   Standard Resistance (Check for Short)

   Tester Connection	Condition	Specified Condition
   B2-5 (VG) or B29-69 (VG) - Body ground	Always	10 kΩ or higher

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

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR (MASS AIR FLOW METER - ECM) 

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 the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off.
6. Turn the ignition switch to ON and turn the Techstream on.
7. Start the engine and warm it up.
8. Drive the vehicle in accordance with the driving pattern described in the Confirmation Driving Pattern.
9. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
10. Read the DTCs.

    Result

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

B → See step   26 

A → END 

NG → REPLACE FUSE (EFI NO. 2 FUSE) 

OK → REPAIR OR REPLACE HARNESS OR CONNECTOR (INTEGRATION RELAY (EFI MAIN RELAY) - AIR FUEL RATIO SENSOR)