The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim consists of both the short-term and the long-term fuel trims.

The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at stoichiometric levels. The signal from the Air-Fuel Ratio (A/F) sensor indicates whether the air-fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel ratio is rich and an increase in the fuel injection volume if it is lean.

factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-term fuel trim compensation.

If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.

DTC No.	DTC Detection Condition	Trouble Area
P0171 P0174	With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to lean side (2 trip detection logic)	Air induction system Injector blockage Mass Air Flow (MAF) meter Engine Coolant Temperature (ECT) sensor Fuel pressure Gas leakage from exhaust system Open or short in A/F sensor (bank 1, 2 sensor 1) circuit A/F sensor (bank 1, 2 sensor 1) A/F sensor heater (bank 1, 2 sensor 1) A/F HTR relay A/F sensor heater and A/F HTR relay circuits PCV valve and hose PCV hose connections ECM
P0172 P0175	With warm engine and stable air-fuel ratio feedback, fuel trim considerably in error to rich side (2 trip detection logic)	Injector leakage or blockage MAF meter ECT sensor Ignition system Fuel pressure Gas leakage from exhaust system Open or short in A/F sensor (bank 1, 2 sensor 1) circuit A/F sensor (bank 1, 2 sensor 1) A/F sensor heater (bank 1, 2 sensor 1) A/F HTR relay A/F sensor heater and A/F HTR relay circuits ECM

HINT:

When DTC P0171 or P0174 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 or P0175 is set, the actual air-fuel ratio is on the rich side.

If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 or P0174 may be set. The MIL is then illuminated.

When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and the engine coolant temperature is more than 75°C [167°F]), the system is functioning normally.

WIRING DIAGRAM

Refer to DTC P2195

INSPECTION PROCEDURE

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: Power train / Engine / Active Test / Control the Injection Volume for A/F Sensor.

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.

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

NOTICE:

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.

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

Following the A/F CONTROL procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.

The following A/F Control procedure enables the technician to check and graph the voltage output of both the heated oxygen sensors. To display the graph, select the following menu items on the tester: View / Line Graph.

HINT:

Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when malfunctions are detected. 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.

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

Connect the intelligent tester to the DLC3.

Turn the engine switch on (IG) and turn the tester ON.

Enter the following menus: Power train / Engine / DTC.

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.

Go to step 12

Go to step 16

A

5.READ VALUE OF ENGINE COOLANT TEMPERATURE SENSOR (COOLANT TEMP)

Connect the intelligent tester to the DLC3.

Turn the engine switch on (IG) and turn the tester ON.

Enter the following menus: Power train / Engine / Data List / Coolant Temp.

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)

Go to step 5

END

LEXUS IS250, IS220d / GSE20 ALE20

4GR-FSE ENGINE CONTROL SYSTEM

Lexus IS250 IS220d GSE20 ALE20

SFI SYSTEM