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 Techstream to the DLC3.
2. Turn the engine switch on (IG) and turn the tester on.
3. Enter the following menus: Powertrain / Engine / Trouble Codes.
4. Read 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 → GO TO DTC CHART 

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 air induction system.

NG → REPAIR OR REPLACE AIR INDUCTION SYSTEM 

OK: Go to next step 

1. Connect Techstream to the DLC3.
2. Start the engine and turn the tester on.
3. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
4. On the tester, enter the following menus: 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 output voltages of the A/F and HO2 sensors (AFS Voltage B1S1 and O2S B1S2 or AFS Voltage B2S1 and O2S B2S2) displayed on the tester.

   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.

   Tester Display (Sensor)	Injection Volume	Status	Voltage
   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	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 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 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.

C → See step   16 

B → See step   12 

A: Go to next step 

1. Connect Techstream to the DLC3.
2. Turn the engine switch on (IG) and turn the tester on.
3. Enter the following menus: Powertrain / Engine / Data List / All Data / Coolant Temp.
4. Read the 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 and 95°C (167 and 203°F)

NG → REPLACE ENGINE COOLANT TEMPERATURE SENSOR 

OK: Go to next step 

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

   • Turn off the engine.
   • Perform the inspection with the vehicle indoors and on a level surface.
   • Perform the inspection of the MAF meter while it is installed to the air cleaner case (installed to the vehicle).
   • During the test, do not use the exhaust air duct to perform suction on the exhaust pipe.
   1. Turn the engine switch on (ACC).
   2. Turn the engine switch on (IG) (do not run the engine).
   3. Turn the tester ON.
   4. Select the following menu items: Powertrain / Engine / Data List / MAF.
   5. Wait 30 seconds, and read the values on the Techstream.

      Standard condition

      Less than 0.58 g/sec.

NG → REPLACE MASS AIR FLOW METER 

OK: Go to next step 

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

NG → CHECK AND REPLACE FUEL PUMP, PRESSURE REGULATOR, FUEL PIPE LINE AND FILTER 

OK: Go to next step 

1. Connect Techstream to the DLC3.
2. Turn the engine switch on (IG) and turn the tester 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 → REPLACE FUEL PRESSURE SENSOR 

OK: Go to next step 

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

NG → CHECK AND REPLACE FUEL PUMP, FUEL PRESSURE SENSOR, WIRING AND FUEL LEAKAGE 

OK: Go to next step 

OK

No gas leakage.

NG → REPAIR OR REPLACE EXHAUST SYSTEM 

OK: Go to next step 

HINT: 

If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using Techstream. Enter the following menus: Powertrain / Engine / Data List / All Data / Cylinder #1 Misfire Count (to Cylinder #6 Misfire Count).

NG → REPAIR OR REPLACE IGNITION SYSTEM 

OK → See step   16 

1. Disconnect the E42 or E38 A/F sensor connector.
   Fig 1: Identifying A/F Sensor Connector Terminals

   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 Connection	Condition	Specified Condition
   HA1A (1) - +B (2)	20°C (68°F)	1.8 to 3.4 Ω
   HA1A (1) - A1A- (4)	-	10 kΩ or higher

   Standard resistance (Bank 2 sensor 1)

   Tester Connection	Condition	Specified Condition
   HA2A (1) - +B (2)	20°C (68°F)	1.8 to 3.4 Ω
   HA2A (1) - A2A- (4)	-	10 kΩ or higher

3. Reconnect the A/F sensor connector.

NG → REPLACE AIR FUEL RATIO SENSOR 

OK: Go to next step 

1. Remove the A/F relay from the engine room R/B No. 2.
   Fig 2: Identifying A/F Relay Test Terminals

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

   Standard resistance

   Tester Connection	Specified Condition
   3 - 5	10 kΩ or higher
   3 - 5	Below 1 Ω (when battery voltage applied to terminals 1 and 2)

3. Reinstall the A/F relay.

NG → REPLACE A/F RELAY 

OK: Go to next step 

1. Disconnect the E42 and E38 A/F sensor connectors.
2. Turn the engine switch on (IG).
3. Measure the voltage according to the value(s) in the table below.

   Standard voltage

   Tester Connection	Specified Condition
   +B (E42-2) - Body ground	9 to 14 V
   +B (E38-2) - Body ground	9 to 14 V

4. Turn the engine switch off.
5. Disconnect the E6 ECM connector.
6. Measure the resistance according to the value(s) in the table below.

   Standard resistance (Check for open)

   Tester Connection	Specified Condition
   HA1A (E42-1) - HA1A (E6-6)	Below 1 Ω
   A1A+ (E42-3) - A1A+ (E6-18)	Below 1 Ω
   A1A- (E42-4) - A1A- (E6-17)	Below 1 Ω
   HA2A (E38-1) - HA2A (E6-4)	Below 1 Ω
   A2A+ (E38-3) - A2A+ (E6-28)	Below 1 Ω
   A2A- (E38-4) - A2A- (E6-27)	Below 1 Ω

   Standard resistance (Check for short)

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

7. Reconnect the ECM connector.
8. Reconnect the A/F sensor connector.
   Fig 3: View Of Heated Oxygen Sensor Circuit Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

NEXT: Go to next step 

1. Drive the vehicle according to the Confirmation Driving Pattern.

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 and wait for 30 seconds.
6. Turn the engine switch on (IG) and turn the Techstream on.
7. Enter the following menus: Powertrain / Engine / Utility / All Readiness.
8. Input the DTC: P0171, P0172, P0174, P0175.
9. Check the DTC judgment result.

   Result

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

B → See step   18 

A → END