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

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.
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 (SENSOR)

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.

A/F SENSOR (SENSOR 1) OUTPUT VOLTAGE

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.