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) and turn the Techstream on.
3. Select the following menu items: Powertrain / Engine / Trouble Codes.
4. Read the DTCs.

   Result

   Display (DTC Output)	Proceed to
   P0171, P0172, P0174 or P0175	A
   P0171, P0172, P0174 or P0175 and other DTCs	B

   HINT: 

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

B → See step   17 

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 leakage.

   OK

   No leakage from the air induction system.

NG → REPAIR OR REPLACE AIR INDUCTION SYSTEM 

OK: Go to next step 

1. Connect the Techstream to the DLC3.
2. Start the engine and turn the Techstream on.
3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
4. Select the following menu items on the Techstream: Powertrain / Engine / Active Test / Control the Injection Volume for A/F Sensor.
5. Perform the Control the Injection Volume for A/F Sensor operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).
6. Monitor the voltage outputs of the A/F and HO2 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.

   Standard voltage

   Techstream Display (Sensor)	Injection Volumes	Status	Voltages
   AFS Voltage B1S1 or AFS Voltage B2S1 (A/F)	+25%	Rich	Less than 3.1 V
   AFS Voltage B1S1 or AFS Voltage B2S1 (A/F)	-12.5%	Lean	More than 3.4 V
   O2S B1S2 or O2S B2S2 (HO2)	+25%	Rich	More than 0.55 V
   O2S B1S2 or O2S B2S2 (HO2)	-12.5%	Lean	Less than 0.4 V

   Result

   Status AFS Voltage B1S1 or AFS Voltage B2S1	Status O2S B1S2 or O2S B2S2	A/F Condition and A/F Sensor Condition	Misfires	Suspected Trouble Areas	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	-	A
   Lean	Lean	Actual air-fuel ratio lean	May occur	PCV valve and hose PCV hose connections Injector blockage Gas leakage from exhaust system Air induction system Fuel pressure Mass Air Flow (MAF) meter Engine Coolant Temperature (ECT) sensor	A
   Rich	Rich	Actual air-fuel ratio rich	-	Injector leakage or blockage Gas leakage from exhaust system Ignition system Fuel pressure MAF meter ECT sensor	A
   Lean	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B
   Rich	Lean/Rich	A/F sensor malfunction	-	A/F sensor	B

   Lean: During Control the Injection Volume for A/F Sensor, the A/F sensor output voltage (AFS) is consistently more than 3.4 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.

   Rich: During Control the Injection Volume for A/F Sensor, the AFS 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.

B → See step   11 

A: Go to next step 

1. Connect the Techstream to the DLC3.
2. Turn the engine switch on (IG) and turn the Techstream on.
3. Select the following menu items: Powertrain / Engine / Data List / Coolant Temp.
4. Read Coolant Temp 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   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 

OK

No gas leakage.

NG → REPAIR OR REPLACE EXHAUST SYSTEM 

OK: Go to next step 

1. Check for sparks and ignition. 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. Select the following menu items: Powertrain / Engine / Data List / Cylinder #1 Misfire Count (to Cylinder #6 Misfire Count).

NG → REPAIR OR REPLACE IGNITION SYSTEM 

OK: Go to next step 

1. Inspect the fuel injector assembly. Refer to INSPECTION .

   HINT: 

   If the injectors malfunction, engine misfire may occur. The misfire count can be read using the Techstream. Select the following menu items: Powertrain / Engine / Data List / Cylinder #1 Misfire Count (to Cylinder #6 Misfire Count).

   Result

   Result	Proceed to
   NG	A
   OK	B

B → See step   15 

A → See step   20 

1. Disconnect the B3 or B4 A/F sensor connector.
   Fig 1: Identifying Air Fuel Ratio Sensor Connectors & Terminals (Banks 1 & 2)

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

   Standard resistance (Bank 1 sensor 1)

   Tester Connections	Specified Conditions
   HT (1) - +B (2)	1.8 to 3.4 Ω at 20°C (68°F)
   HT (1) - AF- (4)	10 kΩ or higher

   Standard resistance (Bank 2 sensor 1)

   Tester Connections	Specified Conditions
   HT (1) - +B (2)	1.8 to 3.4 Ω at 20°C (68°F)
   HT (1) - AF- (4)	10 kΩ or higher

3. Reconnect the A/F sensor connector.

NG → See step   21 

OK: Go to next step 

1. Remove the engine room junction block from the engine room R/B.
   Fig 2: Identifying Engine Room Junction Block

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Measure the A/F relay resistance.

   Standard resistance

   Tester Connections	Specified Conditions
   1G-1 - 1A-4	10 kΩ or higher
   1G-1 - 1A-4	Below 1 Ω (when battery voltage applied to terminals 1E-6 and 1E-11)

3. Reinstall the engine room junction block.

NG → REPLACE ENGINE ROOM JUNCTION BLOCK 

OK: Go to next step 

1. Disconnect the B3 or B4 A/F sensor connector.
2. Turn the engine switch on (IG).
3. Measure the voltage according to the value(s) in the table below.

   Standard voltage

   Tester Connections	Specified Conditions
   +B (B3-2) - Body ground	9 to 14 V
   +B (B4-2) - Body ground	9 to 14 V

4. Turn the engine switch off.
5. Disconnect the B12 ECM connector.
6. Measure the resistance according to the value(s) in the table below.

   Standard resistance (Check for open)

   Tester Connections	Specified Conditions
   HT (B3-1) - HA1A (B12-86)	Below 1 Ω
   AF+ (B3-3) - A1A+ (B12-93)	Below 1 Ω
   AF- (B3-4) - A1A- (B12-116)	Below 1 Ω
   HT (B4-1) - HA2A (B12-109)	Below 1 Ω
   AF+ (B4-3) - A2A+ (B12-120)	Below 1 Ω
   AF- (B4-4) - A2A- (B12-119)	Below 1 Ω

   Standard resistance (Check for short)

   Tester Connections	Specified Conditions
   HT (B3-1) or HA1A (B12-86) - Body ground	10 kΩ or higher
   AF+ (B3-3) or A1A+ (B12-93) - Body ground	10 kΩ or higher
   AF- (B3-4) or A1A- (B12-116) - Body ground	10 kΩ or higher
   HT (B4-1) or HA2A (B12-109) - Body ground	10 kΩ or higher
   AF+ (B4-3) or A2A+ (B12-120) - Body ground	10 kΩ or higher
   AF- (B4-4) or A2A- (B12-119) - Body ground	10 kΩ or higher

7. Reconnect the ECM connector.
8. Reconnect the A/F 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) and turn the Techstream on (Procedure B).
3. Clear the DTCs. Refer to DTC CHECK / CLEAR (Procedure C).
4. Turn the engine switch off.
5. Turn the engine switch on (IG) 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.

NEXT: Go to next step 

1. Select the following menu items: Powertrain / Engine / Trouble Codes / Pending.
2. Read the pending DTCs.

   Result

   Display (DTC Output)	Proceed to
   No output	A
   P0171, P0172, P0174 or P0175	B

B → REPLACE ECM 

A → END