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): Wiring Diagram

WARNING: This page is about a different car, the 2006 Lexus RX 400h. However, it is still accessible from the selected car via links, so may be relevant.

Refer to DTC P2195 .

HINT:

Intelligent tester only:

Malfunctioning areas can be identified by performing the A/F CONTROL function provided in the ACTIVE TEST. The A/F CONTROL function can help to determine whether the Air-Fuel Ratio (A/F) sensor, Heated Oxygen (HO2) sensor and other potential trouble areas are malfunctioning.

The following instructions describe how to conduct the A/F CONTROL operation using an intelligent tester.

Connect the intelligent tester to the DLC3.
Put the engine in inspection mode (See INSPECTION MODE PROCEDURE ).
Start the engine and turn the tester ON.
Warm up the engine at engine speed of 2,500 RPM for approximately 90 seconds.
On the tester, enter the following menus: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL.
Perform the A/F CONTROL 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 B1S1 and O2S B1S2 or AFS B2S1 and O2S B2S2) displayed on the tester.

HINT:

The A/F CONTROL 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

TESTER DISPLAY DIAGNOSIS PROCEDURE

Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS B1S1 or AFS B2S1 (A/F)	+25 %	Rich	Less than 3.0
AFS B1S1 or AFS B2S1 (A/F)	-12.5 %	Lean	More than 3.35
O2S B1S2 or O2S B2S2 (HO2)	+25 %	Rich	More than 0.55
O2S B1S2 or O2S B2S2 (HO2)	-12.5 %	Lean	Less than 0.4

NOTE: The Air-Fuel Ratio (A/F) sensor has an output delay of a few seconds and the Heated Oxygen (HO2) sensor has a maximum output delay of approximately 20 seconds.

AIR-FUEL RATIO CHART

Case	A/F Sensor (Sensor 1) Output Voltage		HO2 Sensor (Sensor 2) Output Voltage		Main Suspected Trouble Area
1	Injection Volume +25% -12.5%	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Injection Volume +25% -12.5%	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	-
1	Output Voltage More than 3.35 V Less than 3.0 V	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Output Voltage More than 0.55 V Less than 0.4 V	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	-
2	Injection Volume +25% -12.5%	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Injection Volume +25% -12.5%	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	A/F sensor A/F sensor heater A/F sensor circuit
2	Output Voltage Almost no reaction	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Output Voltage More than 0.55 V Less than 0.4 V	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	A/F sensor A/F sensor heater A/F sensor circuit
3	Injection Volume +25% -12.5%	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Injection Volume +25% -12.5%	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	HO2 sensor HO2 sensor heater HO2 sensor circuit
3	Output Voltage More than 3.35 V Less than 3.0 V	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Output Voltage Almost no reaction	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	HO2 sensor HO2 sensor heater HO2 sensor circuit
4	Injection volume +25% -12.5%	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Injection Volume +25% -12.5%	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Injector Fuel pressure Gas leakage from exhaust system (Air fuel ratio extremely lean or rich)
4	Output Voltage Almost no reaction	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002	Output Voltage Almost no reaction	Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Following the A/F CONTROL procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.
To display the graph, enter the following menus: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL / USER DATA / AFS B1S1 and O2S B1S2 or AFS B2S1 and O2S B2S2, and press the YES button and then the ENTER button followed by the F4 button.

HINT:

Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was LEAN or RICH, and other data from the time the malfunction occurred.
A low A/F sensor voltage could be caused by a rich air-fuel mixture. Check for conditions that would cause the engine to run rich.
A high A/F sensor voltage could be caused by a rich air-fuel mixture. Check for conditions that would cause the engine to run lean.

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

Connect the intelligent tester to the DLC3.
Turn the ignition switch ON and turn the tester ON.
Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.

Read DTCs.

Result

RESULT CHART

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 DIAGNOSTIC TROUBLE CODE 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 INTELLIGENT TESTER (A/F CONTROL)

Connect the intelligent tester to the DLC3.
Put the engine in inspection mode (See INSPECTION MODE PROCEDURE ).
Start the engine and turn the tester ON.
Warm up the engine at an engine speed of 2,500 RPM for approximately 90 seconds.
On the tester, enter the following menus: DIAGNOSIS / ENHANCED OBD II / ACTIVE TEST / A/F CONTROL.
Perform the A/F CONTROL operation with the engine in an idling condition (press the RIGHT or LEFT button to change the fuel injection volume).

Monitor the outputs voltages of A/F and HO2 sensors (AFS B1S1 and O2S B1S2 or AFS B2S1 and O2S B2S2) displayed on the tester.

HINT:

The A/F CONTROL 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

TESTER DISPLAY DIAGNOSIS PROCEDURE

Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS B1S1 or AFS B2S1 (A/F)	+25 %	Rich	Less than 3.0
AFS B1S1 or AFS B2S1 (A/F)	-12.5 %	Lean	More than 3.35
O2S B1S2 or O2S B2S2 (HO2)	+25 %	Rich	More than 0.55
O2S B1S2 or O2S B2S2 (HO2)	-12.5 %	Lean	Less than 0.4

Result

RESULT CHART

Status AFS B1S1 or AFS 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 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 A/F CONTROL, the A/F sensor output voltage (AFS) is consistently more than 3.35 V, and the HO2 sensor output voltage (O2S) is consistently less than 0.4 V.

Rich: During A/F CONTROL, the AFS is consistently less than 3.0 V, and the O2S is consistently more than 0.55 V.

B: Go to step 10

C: Go to step 14

A: Go to next step

READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)
1. Connect the intelligent tester to the DLC3.
2. Turn the ignition switch ON and turn the tester ON.
3. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / 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 INTELLIGENT TESTER (MAF)
1. Connect the intelligent tester to the DLC3.
2. Turn the tester ON.
3. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / MAF.
4. Read the MAF with the engine stopped.
  Standard:
  
  MAF while engine stopped:
  
  0.54 g/s or less
5. Put the engine in inspection mode (See INSPECTION MODE PROCEDURE ).
6. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / MAF and COOLANT TEMP.
7. Allow the engine to idle until the COOLANT TEMP reaches 75°C (167°F) or more.
8. Read the MAF with the engine in an idling condition and at an engine speed of 2,500 RPM.
  Standard:
  
  MAF while engine idling:
  
  Between 2.0 g/s and 4.3 g/s (shift position: N, A/ C: OFF).
  
  MAF at an engine speed of 2,500 RPM:
  
  Between 12.1 g/s and 18.2 g/s (shift position: N, A/C: OFF).
NG: REPLACE MASS AIR FLOW METER

OK: GO TO NEXT STEP
CHECK FUEL PRESSURE
1. Check the fuel pressure (See ON-VEHICLE INSPECTION ).
  Standard:
  
  304 to 343 kPa (3.1 to 3.5 kgf/cm ² , 44.1 to 49.7 psi)
NG: CHECK AND REPLACE FUEL PUMP, PRESSURE REGULATOR, FUEL PIPE LINE AND FILTER

OK: GO TO NEXT STEP
CHECK FOR EXHAUST GAS LEAKAGE
OK:

No gas leakage.

NG: REPAIR OR REPLACE EXHAUST SYSTEM

OK: GO TO NEXT STEP
CHECK FOR SPARKS AND IGNITION
HINT:

If the spark plugs or ignition system malfunctions, engine misfire may occur. The misfire count can be read using an intelligent tester. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DATA LIST / MISFIRE / CYL #1 (to CYL #6).

NG: REPAIR OR REPLACE IGNITION SYSTEM

OK: GO TO NEXT STEP
INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)
HINT:

If the injectors malfunction, engine misfire may occur. The misfire count can be read using the intelligent tester. Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / CYL #1 (to CYL #6).

NG: REPLACE FUEL INJECTOR ASSEMBLY

OK: GO TO NEXT STEP

INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Disconnect the A3 or A4 A/F sensor connector.

Measure the resistance between the terminals of the A/F sensor connector.

Standard resistance

TESTER CONNECTION SPECIFIED CONDITION CHART

Tester Connection	Specified Condition
HA1A, HA2A - +B	1.8 Ω to 3.4 Ω at 20°C (68°F)
HA1A, HA2A - A1A-, A2A-	10 kΩ or higher

Reconnect the A/F sensor connector.

Fig 1: Inspecting Air Fuel Ratio Sensor (Heater Resistance)
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NG: REPLACE AIR FUEL RATIO SENSOR

OK: GO TO NEXT STEP

INSPECT A/F RELAY

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

Measure the A/F relay resistance.

Standard resistance

TESTER CONNECTION SPECIFIED CONDITION CHART

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.

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

NG: REPLACE A/F RELAY

OK: GO TO NEXT STEP

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

Disconnect the A3 and A4 A/F sensor connector.
Turn the ignition switch ON.

Measure the voltage between the +B terminal of the A/F sensor connector and body ground.

Standard voltage

TESTER CONNECTION SPECIFIED CONDITION CHART

Tester Connection	Specified Condition
+B - Body ground	9 to 14 V

Turn the engine switch off.
Disconnect the H33 HV Control ECU connector.

Measure the resistance between the terminals of the A/F sensor and HV Control ECU.

Standard resistance (Check for open)

TESTER CONNECTION SPECIFIED CONDITION CHART

Tester Connection	Specified Condition
HA1A ( A4-1) - HA1A (H33-4)	Below 1 Ω
A1A+ (A4-3) - A1A+ (H33-22)	Below 1 Ω
A1A- (A4-4) - A1A- (H33-30)	Below 1 Ω
HA2A (A3-1) - HA2A (H33-3)	Below 1 Ω
A2A+ (A3-3) - A2A+ (H33-23)	Below 1 Ω
A2A- (A3-4) - A2A- (H33-31)	Below 1 Ω

Standard resistance (Check for short)

TESTER CONNECTION SPECIFIED CONDITION CHART

Tester Connection	Specified Condition
HA1A ( A4-1) or HA1A (H33-4) - Body ground	10 kΩ or higher
A1A+ (A4-3) or A1A+ (H33-22) - Body ground	10 kΩ or higher
A1A- (A4-4) or A1A- (H33-30) - Body ground	10 kΩ or higher
HA2A (A3-1) or HA2A (H33-3) - Body ground	10 kΩ or higher
A2A+ (A3-3) or A2A+ (H33-23) - Body ground	10 kΩ or higher
A2A- (A3-4) or A2A- (H33-31) - Body ground	10 kΩ or higher

Fig 3: Identifying H33 HV Control ECU Connector

Reconnect the HV Control ECU connector.

NG: REPAIR OR REPLACE HARNESS AND CONNECTOR

OK: GO TO NEXT STEP

REPLACE AIR FUEL RATIO SENSOR
PERFORM CONFIRMATION DRIVING PATTERN
1. Connect the intelligent tester to the DLC3.
  
  Fig 5: Vehicle Speed Graph
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Turn the ignition switch ON and turn the tester ON.
3. Clear DTCs (See DTC CHECK / CLEAR ).
4. Switch the ECM from normal mode to check mode using the tester (See DTC CHECK / CLEAR ).
5. Start the engine and warm it up with all the accessories switched OFF.
6. Drive the vehicle at between 47 mph and 75 mph (75 km/h and 120 km/h) and at an engine speed of between 1,400 RPM and 3,200 RPM for 3 to 5 minutes.
  HINT:
  
  If the system is still malfunctioning, the MIL will be illuminated during step (f).
  
  NOTE: If the conditions in this test are not strictly followed, no malfunction will be detected.

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

On the intelligent tester, enter the following menus: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.

Read DTCS.

Result

RESULT CHART

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

B: Go to step 5

A: END