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

CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174, P0175)

Connect the Techstream to the DLC3.
Turn the ignition switch ON and turn the tester ON.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read the DTCs.

Result

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

B → GO TO RELEVANT DTC CHART

A: Go to next step

CHECK CONNECTION OF PCV HOSE
OK

PCV hose is connected correctly and is not damaged.

NG → REPAIR OR REPLACE PCV HOSE

OK: Go to next step
CHECK AIR INDUCTION SYSTEM
1. Check the air induction system for vacuum leaks.
NG → REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK: Go to next step

PERFORM ACTIVE TEST USING TECHSTREAM (A/F CONTROL)

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
Related DTCs	B1S1	B1S2	B2S1	B2S2	A/F Condition and Heated Oxygen Sensor Condition	Misfire	Main Suspected Trouble Area	Go to Step
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	A
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	May occur	Spark plug, ignition system, injector or exhaust gas leak	B
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	None	Spark plug, ignition system or injector	C
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 0.5 V or more (rich).

D → See step 11

C → See step 10

B → See step 8

A: Go to next step

READ VALUE USING TECHSTREAM (COOLANT TEMP)
1. Connect the Techstream to the DLC3.
2. Enter the following menus: Powertrain / Engine and ECT / 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 → REPLACE ENGINE COOLANT TEMPERATURE SENSOR

OK: Go to next step
READ VALUE USING TECHSTREAM (MAF)
1. Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.
2. Allow the engine to idle until the ECT reaches 75°C (167°F).
3. Read the MAF value at idle RPM.
  Standard
  
  MAF at idle RPM: 4.6 to 5.6 g/sec. (shift lever is in N position and A/C is OFF)
NG → REPLACE MASS AIR FLOW METER

OK: Go to next step
CHECK FUEL PRESSURE
1. Check the fuel pressure. Refer to ON-VEHICLE INSPECTION - Step 2 .
NG → REPAIR OR REPLACE FUEL SYSTEM

OK: Go to next step
CHECK FOR EXHAUST GAS LEAKAGE
NG → REPAIR OR REPLACE EXHAUST SYSTEM

OK: Go to next step
CHECK FOR SPARK AND IGNITION
HINT:

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 and ECT / Data List / Misfire / Cylinder #1 Misfire Count to #8.

NG → REPAIR OR REPLACE IGNITION SYSTEM

OK: Go to next step
INSPECT FUEL INJECTOR
HINT:

If the injectors are malfunctioning, engine misfire may occur. The misfire counter can be read with the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Misfire / Cylinder #1 Misfire Count to #8.

NG → REPLACE FUEL INJECTOR

OK: Go to next step

INSPECT HEATED OXYGEN SENSOR

Fig 1: Identifying Heated Oxygen Sensor Connector Terminals

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Disconnect the H9 and H10 sensor connectors.

Measure the resistance of the heated oxygen sensor.

Standard resistance

Tester Connection	Specified Condition
1 (HT) - 2 (+B)	11 to 16 Ω
1 (HT) - 4 (E1)	10 kΩ or higher

NG → REPLACE HEATED OXYGEN SENSOR

OK: Go to next step

INSPECT EFI RELAY (Marking: EFI)

Fig 2: Inspecting EFI Relay

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Remove the EFI relay from the engine room No. 2 relay block.

Measure the resistance of the EFI relay.

Standard resistance

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

NG → REPLACE EFI RELAY

OK: Go to next step

CHECK WIRE HARNESS (HEATED OXYGEN SENSOR (SENSOR 1) - ECM)

Fig 3: Checking Wire Harness (Heated Oxygen Sensor (Sensor 1) - ECM)

Disconnect the H9 and H10 sensor connectors.
Disconnect the E2 and E4 ECM connectors.

Measure the resistance of the wire harness side connectors.

Standard resistance

Tester Connection	Specified Condition
H9-1 (HT) - E2-24 (HT1A)	Below 1 Ω
H9-3 (OX) - E2-30 (OX1A)	Below 1 Ω
H10-1 (HT) - E4-5 (HT2A)	Below 1 Ω
H10-3 (OX) - E4-28 (OX2A)	Below 1 Ω
H9-1 (HT) or E2-24 (HT1A) - Body ground	10 kΩ or higher
H9-3 (OX) or E2-30 (OX1A) - Body ground	10 kΩ or higher
H10-1 (HT) or E4-5 (HT2A) - Body ground	10 kΩ or higher
H10-3 (OX) or E4-28 (OX2A) - Body ground	10 kΩ or higher

NG → REPAIR OR REPLACE HARNESS AND CONNECTOR

OK: Go to next step

REPLACE HEATED OXYGEN SENSOR
NEXT: Go to next step
PERFORM CONFIRMATION DRIVING PATTERN

Fig 4: Performing Confirmation Driving Pattern
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
- (a) Connect the Techstream to the DLC3.
- (b) Switch the tester from normal mode to check mode. Refer to CHECK MODE PROCEDURE .
- (c) Allow the engine to idle until the ECT reaches 75°C (167°F).
- (d) Allow the vehicle to run at 40 km/h (25 mph) or more for 25 seconds or more.
- (e) Allow the engine to idle for 30 seconds or more.
- (f) Perform steps (d) and (e) at least 3 times.
  HINT:
  
  If a malfunction exists, the MIL will be illuminated on the multi-information display.
  
  NOTE:
  If the conditions in this test are not strictly followed, you should perform steps (d) and (e).
  
  If you do not have the Techstream, turn the ignition switch OFF after performing steps (c) and (f), and then perform steps (c) and (f) again.
- (g) Allow the engine to idle for 30 seconds.
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