DTC P0171: System Too Lean (Bank 1); DTC P0172: System Too Rich (Bank 1); DTC P0174: System Too Lean (Bank 2); DTC P0175: System Too Rich (Bank 2): Procedure

1. Connect the Techstream to the DLC3.
2. Turn the engine switch on (IG).
3. Turn the Techstream on.
4. Enter the following menus: Powertrain / Engine / Trouble Codes.
5. Read the DTCs.

   Result

   Result	Proceed to
   DTC P0171, P0172, P0174 and/or P0175 are output	A
   DTC P0171, P0172, P0174 or P0175 and other DTCs are output	B

   HINT: 

   If any DTCs other than P0171, P0172, P0174 or P0175 are output, troubleshoot those DTCs first.

B → See step   22 

A: Go to next step 

1. Check 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 - Step 1 .

   OK

   No leaks in the 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 / Active Test / Control the Injection Volume for A/F Sensor.
6. Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
7. Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the Techstream.

   HINT: 

   • 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.

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

   Result

   Status AFS Voltage B1S1 or AFS Voltage B2S1	Status O2S B1S2 or O2S B2S2	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 Engine coolant temperature sensor Fuel pressure 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 Engine coolant temperature sensor Fuel pressure 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 for A/F Sensor Active Test, 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 the Control the Injection Volume for A/F Sensor Active Test, the AFS Voltage is consistently less than 3.1 V, and the O2S is consistently more than 0.55 V.

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

C → See step   29 

B → See step   13 

A: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the engine switch on (IG).
3. Turn the Techstream on.
4. Enter the following menus: Powertrain / Engine / Data List / Coolant Temp.
5. Read the Data List twice, when the engine is both cold and warmed up.

   Standard

   With cold engine 

   Same as ambient air temperature.

   With warm engine 

   Between 75°C and 95°C (167°F and 203°F)

NG → See step   23 

OK: Go to next step 

1. Inspect the mass air flow meter. Refer to PROCEDURE - Step 4 .

NG → See step   24 

OK: Go to next step 

1. Check the fuel pressure (low pressure side). Refer to ON-VEHICLE INSPECTION - Step 2 .

NG → REPAIR OR REPLACE FUEL SYSTEM (LOW PRESSURE SIDE) 

OK: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the engine switch on (IG) and turn the Techstream on.
3. Start the engine.
4. Enter the following menus: Powertrain / Engine / Data List / Fuel Press.
5. While revving the engine, check that the fuel pressure fluctuates.

   OK

   Fuel pressure fluctuates.

NG → See step   28 

OK: Go to next step 

1. Check the fuel pressure (high pressure side). Refer to ON-VEHICLE INSPECTION - Step 3 .

NG → REPAIR OR REPLACE FUEL SYSTEM (HIGH PRESSURE SIDE) 

OK: Go to next step 

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

   OK

   No gas leaks

NG → REPAIR OR REPLACE EXHAUST GAS LEAK POINT 

OK: Go to next step 

1. Check the ignition system. Refer to ON-VEHICLE INSPECTION - Step 1 .

NG → REPAIR OR REPLACE IGNITION SYSTEM 

OK: Go to next step 

1. Inspect the fuel injector assembly. Refer to INSPECTION .
2. Inspect the cold start injector. Refer to INSPECTION .

NG → See step   25 

OK: Go to next step 

NG → See step   26 

OK: Go to next step 

NG → See step   18 

OK: Go to next step 

1. Disconnect the air fuel ratio sensor connector.
   Fig 1: Identifying Air Fuel Ratio Sensor Connector

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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
   E42-1 (HA1A) - E6-6 (HA1A)	Always	Below 1 Ω
   E42-3 (A1A+) - E6-18 (A1A+)	Always	Below 1 Ω
   E42-4 (A1A-) - E6-17 (A1A-)	Always	Below 1 Ω
   E38-1 (HA2A) - E6-4 (HA2A)	Always	Below 1 Ω
   E38-3 (A2A+) - E6-28 (A2A+)	Always	Below 1 Ω
   E38-4 (A2A-) - E6-27 (A2A-)	Always	Below 1 Ω

   Standard Resistance (Check for Short)

   Tester Connection	Condition	Specified Condition
   E42-1 (HA1A) or E6-6 (HA1A) - Body ground	Always	10 kΩ or higher
   E42-3 (A1A+) or E6-18 (A1A+) - Body ground	Always	10 kΩ or higher
   E42-4 (A1A-) or E6-17 (A1A-) - Body ground	Always	10 kΩ or higher
   E38-1 (HA2A) or E6-4 (HA2A) - Body ground	Always	10 kΩ or higher
   E38-3 (A2A+) or E6-28 (A2A+) - Body ground	Always	10 kΩ or higher
   E38-4 (A2A-) or E6-27 (A2A-) - 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)
   *3	Bank 1	*4	Bank 2

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

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 engine switch on (IG).
3. Turn the Techstream on.
4. Clear the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the engine switch off.
6. Turn the engine switch on (IG) 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 / Utility / All Readiness.
10. Input the DTC: P0171, P0172, P0174 or P0175.
11. Check the DTC judgment result.

    Result

    Result	Proceed to
    NORMAL (DTC is not output)	A
    ABNORMAL (DTC P0171, P0172, P0174 and/or P0175 are output)	B

B → See step   27 

A → END 

NG → REPLACE RELAY (A/F RELAY) 

OK: Go to next step 

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK → REPAIR OR REPLACE HARNESS OR CONNECTOR (EFI MAIN RELAY - A/F RELAY) 

1. Connect the Techstream to the DLC3.
2. Turn the engine switch on (IG).
3. Turn the Techstream on.
4. Clear the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the engine switch off.
6. Turn the engine switch on (IG) 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 / Utility / All Readiness.
10. Input the DTC: P0171, P0172, P0174 or P0175.
11. Check the DTC judgment result.

    Result

    Result	Proceed to
    NORMAL (DTC is not output)	A
    ABNORMAL (DTC P0171, P0172, P0174 and/or P0175 are output)	B

B → See step   31 

A → See step   30