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 ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171, P0172, P0174 OR P0175)

Connect Techstream to the DLC3.
Turn the engine switch on (IG) and turn the tester on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

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

CHECK 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 leakage.
  OK
  
  No leakage from air induction system.
NG → REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK: Go to next step

PERFORM ACTIVE TEST USING TECHSTREAM (A/F CONTROL)

Connect Techstream to the DLC3.
Start the engine and turn the tester on.
Warm up the engine at an engine speed of 2500 RPM for approximately 90 seconds.
On the tester, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
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).

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 B2S1 (A/F)	+25%	Rich	Less than 3.1 V
AFS Voltage B1S1 or AFS 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

READ VALUE USING ENGINE COOLANT TEMPERATURE SENSOR (COOLANT TEMP)
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 and ECT / 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
READ VALUE USING INTAKE AIR FLOW METER (MAF)
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 and ECT / Data List / MAF.
  5. Wait 30 seconds, and read the values on the Techstream.
    Standard condition
    
    Less than 0.36 g/sec.
NG → REPLACE MASS AIR FLOW METER

OK: Go to next step
CHECK FUEL PRESSURE (LOW PRESSURE SIDE)
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
CHECK FUEL PRESSURE SENSOR
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 and ECT / 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
CHECK FUEL PRESSURE (HIGH PRESSURE SIDE)
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
CHECK FOR EXHAUST GAS LEAK
OK

No 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 malfunctions, engine misfire may occur. The misfire count can be read using Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Cylinder #1 Misfire Rate (to Cylinder #6 Misfire Rate).

NG → REPAIR OR REPLACE IGNITION SYSTEM

OK: Go to next step

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Disconnect the E42 or E38 A/F sensor connector.

Fig 1: Identifying Connector Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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

Reconnect the A/F sensor connector.

NG → REPLACE AIR FUEL RATIO SENSOR

OK: Go to next step

INSPECT A/F RELAY

Remove the A/F relay from the engine room R/B No. 2.

Fig 2: Identifying Relay Test Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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)

Reinstall the A/F relay.

NG → REPLACE A/F RELAY

OK: Go to next step

CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)

Disconnect the E42 and E38 A/F sensor connectors.

Fig 3: Identifying Connector Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Turn the engine switch on (IG).

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

Turn the engine switch off.
Disconnect the E6 ECM connector.

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

Reconnect the ECM connector.
Reconnect the A/F sensor connector.

Fig 4: Heated Oxygen (A/F) Sensor Circuit Diagram
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

REPLACE AIR FUEL RATIO SENSOR
NEXT: Go to next step
PERFORM CONFIRMATION DRIVING PATTERN
1. Connect Techstream to the DLC3. (Procedure "A")
  
  Fig 5: Confirmation Driving Pattern
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Turn the engine switch on (IG) and turn the tester on. (Procedure "B")
3. Clear DTCs. Refer to DTC CHECK / CLEAR . (Procedure "C")
4. Switch the ECM from normal mode to check mode using the tester. Refer to CHECK MODE PROCEDURE . (Procedure "D")
5. Start the engine and warm it up with all the accessories switched OFF. (Procedure "E")
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. (Procedure "F")
  HINT:
  
  If the system is still malfunctioning, the MIL will be illuminated during procedure "F".
  
  NOTE:
  If the conditions in this test are not strictly followed, no malfunction will be detected.
NEXT: Go to next step

CHECK WHETHER DTC OUTPUT RECURS (DTC P0171, P0172, P0174 OR P0175)

On Techstream, enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read DTCs.

Result

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

B → See step 5

A → END