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   17 

A: Go to next step 

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

   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 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. 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).
7. Monitor the voltage outputs of the air fuel ratio sensor and the heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) 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.

   Standard

   Techstream 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 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	-	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, 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.

C → See step   15 

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 value

   With cold engine: Same as ambient air temperature.

   With warm engine: 80 to 100°C (176 to 212°F).

NG → See step   18 

OK: Go to next step 

1. Inspect the mass air flow meter . Refer to ON-VEHICLE INSPECTION .

NG → See step   19 

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. Inspect for exhaust gas leaks.

   OK

   No gas leaks.

NG → REPAIR OR REPLACE EXHAUST SYSTEM 

OK: Go to next step 

HINT: 

• Refer to the ignition system inspection procedure . Refer to ON-VEHICLE INSPECTION - Step 1 .
• If the spark plugs or ignition system malfunctions, engine misfires 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 

HINT: 

• Refer to the fuel injector inspection procedure . Refer to INSPECTION .
• If the injectors malfunction, engine misfires 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 → See step   20 

OK: Go to next step 

NG → See step   21 

OK: Go to next step 

NG → See step   23 

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 

Fig 1: View Of Vehicle Speed Driving Pattern

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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. Start the engine and warm it up with all the accessories switched off.
6. Drive the vehicle at between 38 mph and 75 mph (60 km/h and 120 km/h) and at an engine speed of between 1400 rpm and 3200 rpm for 3 to 5 minutes.

   HINT: 

   If the system is still malfunctioning, the MIL will be illuminated during step (f).

   NOTE:

   If the conditions in this test are not strictly followed, no malfunction will be detected.

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 and ECT / Trouble Codes / Pending.
5. Read the DTCs.

   Result

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

B → See step   22 

A → END 

1. Remove the EFI No. 2 fuse from the engine room relay block.
   Fig 2: Identifying EFI No. 2 Fuse

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   EFI No. 2 fuse	Always	Below 1 Ω

3. Reinstall the EFI No. 2 fuse.

NG → REPLACE FUSE (EFI NO. 2 FUSE) 

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