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 and ECT / Trouble Codes.
4. Read DTCs.
   RESULT
   
   

   Result	Proceed to
   P0171, P0172, P0174 or P0175 is output	A
   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   23 

A: Go to next step 

NG → REPAIR OR REPLACE PCV HOSE 

OK: Go to next step 

NG → REPAIR OR REPLACE INTAKE 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. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.
5. Perform the Control the Injection Volume 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 operation lowers the fuel injection volume by 12% or increases the injection volume by 12%.
   • Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
   • The A/F sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.
   • If the sensor output voltage does not change (almost no reaction) while performing the Active Test, the sensor may be malfunctioning.

   Standard Voltage

   Techstream Display (Sensor)	Injection Volumes	Status	Voltages
   AFS Voltage B1S1 or AFS Voltage B2S1 (A/F)	+12%	Rich	Less than 3.1 V
   	-12%	Lean	More than 3.4 V
   O2S B1S2 or O2S B2S2 (HO2)	+12%	Rich	More than 0.55 V
   	-12%	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	Suspected Trouble Areas	Proceed to
   Lean/Rich	Lean/Rich	Normal	-	A
   Lean	Lean	Actual air-fuel ratio lean	PCV valve and hose PCV hose connections Injector blockage Gas leak from exhaust system Intake system Fuel pressure Mass Air Flow (MAF) meter Engine Coolant Temperature (ECT) sensor
   Rich	Rich	Actual air-fuel ratio rich	Injector leakage or blockage Gas leak from exhaust system Ignition system Fuel pressure MAF meter ECT sensor
   Lean	Lean/Rich	A/F sensor malfunction	A/F sensor	B
   Rich

   Lean: During Control the Injection Volume, 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, 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 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 ignition switch to ON and turn the Techstream on.
3. Enter the following menus: Powertrain / Engine and ECT / Data List / 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°C and 100°C (167°F and 212°F).

NG → See step   24 

OK: 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 / MAF and Coolant Temp.
5. Allow the engine to idle until Coolant Temp reaches 75°C (167°F) or higher.
6. Read MAF with the engine speed at 3000 rpm.

   Standard

   Between 18.3 gm/sec. and 25.8 gm/sec. (shift lever: N; A/C: Off).

NG → See step   16 

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. Check 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 .
• If the spark plugs or ignition system malfunctions, engine misfire 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 #6 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 misfire 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 #6 Misfire Count).

OK → See step   15 

NG → See step   25 

NG → See step   26 

OK: Go to next step 

Fig 1: Checking Terminal Voltage (+B Of A/F Sensor)

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

1. Disconnect the A/F sensor connector.
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
   B33-2 (+B) - Body ground	Ignition switch ON	11 to 14 V
   B31-2 (+B) - Body ground	Ignition switch ON	11 to 14 V

   TEXT IN ILLUSTRATION
   
   

   *1	Front view of wire harness connector (to A/F Sensor)
   *2	Bank 1
   *3	Bank 2

NG → See step   21 

OK: Go to next step 

1. Disconnect the A/F sensor connector.
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
   B33-1 (HA1A) - B50-17 (HA1A)	Always	Below 1 Ω
   B33-3 (A1A+) - B49-1 (A1A+)	Always	Below 1 Ω
   B33-4 (A1A-) - B49-2 (A1A-)	Always	Below 1 Ω
   B31-1 (HA2A) - B50-19 (HA2A)	Always	Below 1 Ω
   B31-3 (A2A+) - B49-7 (A2A+)	Always	Below 1 Ω
   B31-4 (A2A-) - B49-8 (A2A-)	Always	Below 1 Ω

   Standard Resistance (Check for Short)

   Tester Connection	Condition	Specified Condition
   B33-1 (HA1A) or B50-17 (HA1A) - Body ground	Always	10 kΩ or higher
   B33-3 (A1A+) or B49-1 (A1A+) - Body ground	Always	10 kΩ or higher
   B33-4 (A1A-) or B49-2 (A1A-) - Body ground	Always	10 kΩ or higher
   B31-1 (HA2A) or B50-19 (HA2A) - Body ground	Always	10 kΩ or higher
   B31-3 (A2A+) or B49-7 (A2A+) - Body ground	Always	10 kΩ or higher
   B31-4 (A2A-) or B49-8 (A2A-) - Body ground	Always	10 kΩ or higher

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Replace the A/F sensor. Refer to REMOVAL .

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. Clear the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off.
6. Turn the ignition switch to ON 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. Read pending DTCs.
   RESULT
   
   

   Result	Proceed to
   No DTC is output	A
   DTC P0171, P0172, P0174 or P0175 is output	B

B → See step   16 

A → END 

1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM. Refer to ELECTRONIC CIRCUIT INSPECTION PROCEDURE .

   HINT: 

   Repair any problems.

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. Clear the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off.
6. Turn the ignition switch to ON 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 Confirmation Driving Pattern.
9. Read pending DTCs.
   RESULT
   
   

   Result	Proceed to
   P0171, P0172, P0174 or P0175 is output	A
   No output	B

B → END 

A: Go to next step 

1. Disconnect the Mass Air Flow (MAF) meter connector.
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
   B51-5 (VG) - B48-14 (VG)	Always	Below 1 Ω
   B51-4 (E2G) - B48-13 (E2G)	Always	Below 1 Ω

   Standard Resistance (Check for Short)

   Tester Connection	Condition	Specified Condition
   B51-5 (VG) or B48-14 (VG) - Body ground	Always	10 kΩ or higher

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Replace the MAF meter assembly. Refer to REMOVAL .

   HINT: 

   If the result of the inspection performed in step 6 indicated no problem, proceed to the next step without replacing the mass air flow meter assembly.

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. Clear the DTCs. Refer to DTC CHECK / CLEAR .
5. Turn the ignition switch off.
6. Turn the ignition switch to ON 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 Confirmation Driving Pattern.
9. Read pending DTCs.
   RESULT
   
   

   Result	Proceed to
   No output	A
   P0171, P0172, P0174 or P0175 is output	B

B → REPLACE ECM 

A → END 

1. Disconnect the A/F sensor connector.
2. Remove the A/F heater relay from the engine room relay block.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance (Check for Open)

   Tester Connection	Switch Condition	Specified Condition
   B33-2 (+B) - 3 (A/F HEATER relay holder)	Always	Below 1 Ω
   B31-2 (+B) - 3 (A/F HEATER relay holder)	Always	Below 1 Ω

   Standard Resistance (Check for Short)

   Tester Connection	Switch Condition	Specified Condition
   B33-2 (+B) or 3 (A/F HEATER relay holder) - Body ground	Always	10 kΩ or higher
   B31-2 (+B) or 3 (A/F HEATER relay holder) - Body ground	Always	10 kΩ or higher

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR 

OK: Go to next step 

1. Inspect the A/F HEATER relay. Refer to ON-VEHICLE INSPECTION .

NG → See step   27 

OK → See step   28