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 ignition switch to ON and turn the Techstream on.
3. Enter the following menus: Powertrain / Engine / Trouble Codes.
4. Read the DTCs.

   Result

   Result	Proceed to
   P0171, P0172, P0174 or P0175	A
   P0171, P0172, P0174 or P0175 and other DTCs	B

B → See step   18 

A: Go to next step 

OK

PCV hose is connected correctly and is not damaged.

NG → REPAIR OR REPLACE PCV HOSE 

OK: Go to next step 

1. Check the air induction system for vacuum leaks.

NG → REPAIR OR REPLACE AIR INDUCTION SYSTEM 

OK: Go to next step 

1. Perform the Active Test Control the Injection Volume for A/F Sensor with the Techstream and check the heated oxygen sensor status.

   Standard Voltage

   Heated oxygen sensor reacts in accordance with the increase and decrease of injection volume:

   +25% → Rich output: More than 0.55 V

   -12.5% → Lean output: Less than 0.4 V

   Related DTCs	Heated Oxygen Sensor Status				A/F Condition and Heated Oxygen Sensor Condition	Misfire	Main Suspected Trouble Area	Go to Step
   	B1S1	B1S2	B2S1	B2S2
   N/A	L/R	L/R	L/R	L/R	Normal	None	None	N/A
   P0171 P0174	L	L	L	L	Actual A/F is lean at all cylinders	May occur	PCV hose, air induction system, fuel pressure, MAF or ECT	A
   P0172 P0175	R	R	R	R	Actual A/F is rich at all cylinders	None	Fuel pressure, MAF or ECT
   P0171	L	L	L/R	L/R	Actual A/F is lean at bank 1	May occur	Spark plug, ignition system, injector or exhaust gas leak	B
   P0174	L/R	L/R	L	L	Actual A/F is lean at bank 2
   P0172	R	R	L/R	L/R	Actual A/F is rich at bank 1	None	Spark plug, ignition system or injector	C
   P0175	L/R	L/R	R	R	Actual A/F is rich at bank 2
   P0171	L	R	L/R	L/R	Heated oxygen sensor (bank 1 sensor 1) malfunction	None	Heated oxygen sensor (bank 1 sensor 1)	D
   P0174	L/R	L/R	L	R	Heated oxygen sensor (bank 2 sensor 1) malfunction	None	Heated oxygen sensor (bank 2 sensor 1)
   P0172	R	L	L/R	L/R	Heated oxygen sensor (bank 1 sensor 1) malfunction	None	Heated oxygen sensor (bank 1 sensor 1)
   P0175	L/R	L/R	R	L	Heated oxygen sensor (bank 2 sensor 1) malfunction	None	Heated oxygen sensor (bank 2 sensor 1)

   HINT: 

   L: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor almost always indicates 0.4 V or less (lean).

   R: During Control the Injection Volume for A/F Sensor of the Active Test, the output voltage of the heated oxygen sensor almost always indicates 0.55 V or more (rich).

D → See step   11 

C → See step   10 

B → See step   8 

A: Go to next step 

1. Connect the Techstream to the DLC3.
2. Enter the following menus: Powertrain / Engine / Data List / Coolant Temp.
3. Read the Coolant Temp value when the engine is cold and warmed up.

   Standard

   ECT when the engine is cold: Same as ambient temperature

   ECT when the engine is warmed up: 75 to 95°C (167 to 203°F)

NG → See step   19 

OK: Go to next step 

1. Read the values using the Techstream (MAF).
   NOTE:

   • Turn the ignition switch to OFF.
   • Perform the inspection with the vehicle indoors and on a level surface.
   • Perform the inspection of the mass air flow meter while it is installed in the air cleaner case (installed on the vehicle).
   • During the test, do not use the exhaust air duct to perform suction on the exhaust pipe.
   1. Connect the Techstream to the DLC3.
   2. Turn the ignition switch to ON (do not start the engine).
   3. Turn the Techstream on.
   4. Enter the following menus: Powertrain / Engine / Data List / MAF.
   5. Wait for 30 seconds, and read the values on the Techstream.

      Standard

      Less than 0.51 g/sec

2. Inspect the mass air flow meter.
   Fig 1: Inspecting Mass Air Flow Meter

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. Remove the mass air flow meter. Refer to REMOVAL .
   2. Using a work light, check that the platinum filament (heater portion) in the mass air flow meter has no foreign matter attached.

      OK

      No foreign matter attached.

NG → See step   20 

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 

OK

No gas leak.

NG → REPAIR OR REPLACE EXHAUST SYSTEM 

OK: Go to next step 

HINT: 

• Refer to the ignition system inspection procedure. Refer to ON-VEHICLE INSPECTION .
• If the spark plugs or ignition system malfunction, engine misfire may occur. The misfire counter can be read with the Techstream. Enter the following menus: Powertrain / Engine / Data List / Cylinder #1 Misfire Count to #8.

NG → REPAIR OR REPLACE IGNITION SYSTEM 

OK: Go to next step 

HINT: 

• Refer to the fuel injector inspection procedure. Refer to INSPECTION .
• If the injectors are malfunctioning, engine misfire may occur. The misfire counter can be read with the Techstream. Enter the following menus: Powertrain / Engine / Data List / Cylinder #1 Misfire Count to #8.

NG → REPLACE FUEL INJECTOR 

OK → See step   15 

NG → REPLACE HEATED OXYGEN SENSOR 

OK: Go to next step 

Fig 2: Identifying Heated Oxygen Sensor Connector

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. Disconnect the heated oxygen sensor connectors.
2. Turn the ignition switch to ON.
3. Measure the voltage according to the value(s) in the table below.

   Standard Voltage

   Tester Connection	Switch Condition	Specified Condition
   H9-2 (+B) - Body ground	Ignition switch ON	11 to 14 V
   H10-2 (+B) - Body ground	Ignition switch ON	11 to 14 V

NG → See step   17 

OK: Go to next step 

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Replace the heated oxygen sensor (sensor 1).

NEXT: Go to next step 

1. Refer to the confirmation driving pattern for P0171, P0172, P0173 and P0174.

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. Enter the following menus: Powertrain / Engine / Trouble Code / Pending.
5. Read the Pending DTCs.

   Result

   Result	Proceed to
   No output	A
   P0171, P0172, P0173 or P0174	B

B → See step   21 

A → END 

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK → See step   22