1Az-Fe Engine Control System. Dtc P0171 System Too Lean (Bank 1)

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 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 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.

DTC No.	DTC Detection Condition	Trouble Area
P0171	With a warm engine and stable air-fuel ratio feedback, the fuel trim is considerably in error to the lean side (2 trip detection logic).	Air induction system Fuel injector blockage Mass air flow meter assembly Engine coolant temperature sensor Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor circuit Air fuel ratio sensor Air fuel ratio sensor heater No. 1 integration relay Air fuel ratio sensor heater and No. 1 integration relay circuits PCV valve and hose PCV hose connections ECM Wire harness or connector
P0172	With a warm engine and stable air-fuel ratio feedback, the fuel trim is considerably in error to the rich side (2 trip detection logic).	Fuel injector leak or blockage Mass air flow meter assembly Engine coolant temperature sensor Ignition system Fuel pressure Gas leak from exhaust system Open or short in air fuel ratio sensor circuit Air fuel ratio sensor Air fuel ratio sensor heater No. 1 integration relay Air fuel ratio sensor heater and No. 1 integration relay circuits ECM Wire harness or connector

HINT:

When DTC P0171 is stored, the actual air-fuel ratio is on the lean side. When DTC P0172 is stored, 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 may be stored. 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 higher than 75°C [167°F]), the system is functioning normally.

MONITOR DESCRIPTION

Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the ECM estimated fuel injection volumes also affect the average fuel trim learning value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learning value of the air-fuel ratio). If the average fuel trim learning value exceeds the malfunction threshold, the ECM interprets this as a fault in the fuel system and stores a DTC.
Example:
If the average fuel trim learning value is +35% or more, or -35% or less, the ECM interprets this as a fuel system malfunction.

Toyota Rav4. Aca30, 33, 38 Gsa33 Zsa30, 35.1Az-Fe Engine Control System.Sfi System.
Dtc
P0171 System Too Lean (Bank 1)

WIRING DIAGRAM

Refer to DTC P2195 (RAV4_ACA30 RM000000WC40NAX_07.html).

INSPECTION PROCEDURE

HINT:

Read freeze frame data using the intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, 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 air fuel ratio sensor voltage could be caused by a rich air-fuel mixture. Check for conditions that would cause the engine to run rich.
A high air fuel ratio sensor voltage could be caused by a lean air-fuel mixture. Check for conditions that would cause the engine to run lean.

1.CHECK FOR 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 (IG).

Turn the tester on.

Enter the following menus: Powertrain / Engine and ECT / DTC.

Read DTCs.
Result
Result
Proceed to
DTC P0171 or P0172 is output
A
DTC P0171 or P0172 and other DTCs are output
B

Result
Result	Proceed to
DTC P0171 or P0172 is output	A
DTC P0171 or P0172 and other DTCs are output	B

HINT:

If any DTCs other than P0171 or P0172 are output, troubleshoot those DTCs first.

GO TO DTC CHART (RAV4_ACA30 RM000000PDF0FLX.html)

A

2.CHECK PCV HOSE CONNECTIONS

Check the PCV hose connections.
OK:
PCV hose is connected correctly and is not damaged.

REPAIR OR REPLACE PCV HOSE

OK

3.CHECK AIR INDUCTION SYSTEM

Check the air induction system for vacuum leaks (RAV4_ACA30 RM000001RLS00FX_01_0002.html).
OK:
No leaks in air induction system.

REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK

4.PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE INJECTION VOLUME)

Connect the intelligent tester to the DLC3.

Start the engine.

Turn the tester on.

Warm up the engine and run the engine at an engine speed of 2500 rpm for approximately 90 seconds.

Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume.

Perform the Control the Injection Volume operation with the engine idling.

Monitor the output voltages of the air fuel ratio and heated oxygen sensors (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.

HINT:

Change the fuel injection volume within the range of -12.0% to +12.0%. The injection volume can be changed in fine gradations.
The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.

Tester Display (Sensor)	Injection Volume	Status	Voltage
AFS Voltage B1S1 (Air fuel ratio)	+12%	Rich	Below 3.1 V
AFS Voltage B1S1 (Air fuel ratio)	-12%	Lean	Higher than 3.4 V
O2S B1S2 (Heated oxygen)	+12%	Rich	Higher than 0.55 V
O2S B1S2 (Heated oxygen)	-12%	Lean	Below 0.4 V

Result:

Status of AFS Voltage B1S1	Status of O2S B1S2	Air Fuel Ratio Condition and Air Fuel Ratio Sensor Condition	Misfire	Suspected Trouble Area	Proceed to
Lean/Rich	Lean/Rich	Normal	-	-	A
Lean	Lean	Actual air fuel ratio lean	May occur	PCV valve and hose PCV hose connections Fuel injector assembly blockage Gas leaks from exhaust system Intake system Fuel pressure Mass air flow meter assembly Engine coolant temperature sensor	A
Rich	Rich	Actual air fuel ratio rich	-	Fuel injector assembly leakage or blockage Gas leaks from exhaust system Ignition system Fuel pressure Mass air flow meter assembly Engine coolant temperature sensor	A
Lean	Lean/Rich	Air fuel ratio sensor malfunction	-	Air fuel ratio sensor	B
Rich	Lean/Rich	Air fuel ratio sensor malfunction	-	Air fuel ratio sensor	B

Lean: During the Control the Injection Volume Active Test, the air fuel ratio sensor output voltage (AFS Voltage) is consistently higher than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently below 0.4 V.
Rich: During the Control the Injection Volume Active Test, the AFS Voltage is consistently below 3.1 V, and the O2S is consistently higher than 0.55 V.
Lean/Rich: During the Control the Injection Volume Active Test, the output voltage of the heated oxygen sensor alternates correctly.

HINT:

Refer to "Data List / Active Test" [AFS Voltage B1S1, O2S B1S2] (RAV4_ACA30 RM000000PDN0GZX.html).

Go to step 11

A

5.READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)

Connect the intelligent tester to the DLC3.

Turn the ignition switch on (IG).

Turn the tester on.

Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp.

Read 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°C and 100°C (167°F and 212°F).

REPLACE ENGINE COOLANT TEMPERATURE SENSOR (RAV4_ACA30 RM0000017U900UX.html)

OK

6.READ VALUE USING INTELLIGENT TESTER (MAF)

Connect the intelligent tester to the DLC3.

Turn the ignition switch on (IG).

Turn the tester on.

Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / MAF and Coolant Temp.

Allow the engine to idle until Coolant Temp reaches 75°C (167°F) or higher.

Read MAF with the engine speed at 3000 rpm.
Standard:
Between 7 gm/s and 12 gm/s (shift position: N; A/C: OFF).

Go to step 16

OK

7.CHECK FUEL PRESSURE

Check the fuel pressure (RAV4_ACA30 RM000000QE3013X_02_0005.html).

REPAIR OR REPLACE FUEL SYSTEM

OK

8.CHECK FOR EXHAUST GAS LEAK

Check for exhaust gas leaks.
OK:
No gas leaks.

REPAIR OR REPLACE EXHAUST SYSTEM

OK

9.CHECK FOR SPARKS AND IGNITION

Check for the sparks and ignition (RAV4_ACA30 RM000001QVP01KX_01_0001.html).

REPAIR OR REPLACE IGNITION SYSTEM

OK

10.INSPECT FUEL INJECTOR ASSEMBLY (INJECTION AND VOLUME)

Check the injection and volume (RAV4_ACA30 RM000000VZW010X_01_0001.html).

Go to step 15

REPLACE FUEL INJECTOR ASSEMBLY (RAV4_ACA30 RM0000017R800PX.html)

11.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)

Inspect the air fuel ratio sensor (RAV4_ACA30 RM000001Z1P00UX_01_0001.html).

REPLACE AIR FUEL RATIO SENSOR (RAV4_ACA30 RM000001RO300SX.html)

OK

12.CHECK TERMINAL VOLTAGE (+B OF AIR FUEL RATIO SENSOR)

Disconnect the air fuel ratio sensor connector.

Measure the voltage according to the value(s) in the table below.
Standard Voltage:
Tester Connection
Condition
Specified Condition
B7-2 (+B) - Body ground
Ignition switch on (IG)
11 to 14 V

Reconnect the air fuel ratio sensor connector.

Go to step 21

OK

13.CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - ECM)

Disconnect the air fuel ratio sensor connector.

Disconnect the ECM connector.

Measure the resistance according to the value(s) in the table below.

Standard Resistance (Check for Open):

Tester Connection	Condition	Specified Condition
B7-1 (HA1A) - B32-109 (HA1A)	Always	Below 1 Ω
B7-3 (A1A+) - B32-112 (A1A+)	Always	Below 1 Ω
B7-4 (A1A-) - B32-113 (A1A-)	Always	Below 1 Ω

Standard Resistance (Check for Short):

Tester Connection	Condition	Specified Condition
B7-1 (HA1A) or B32-109 (HA1A) - Body ground	Always	10 kΩ or higher
B7-3 (A1A+) or B32-112 (A1A+) - Body ground	Always	10 kΩ or higher
B7-4 (A1A-) or B32-113 (A1A-) - Body ground	Always	10 kΩ or higher

Reconnect the ECM connector.

Reconnect the air fuel ratio sensor connector.

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

14.REPLACE AIR FUEL RATIO SENSOR

Replace the air fuel ratio sensor (RAV4_ACA30 RM000001RO300SX.html).

NEXT

15.PERFORM CONFIRMATION DRIVING PATTERN

Connect the intelligent tester to the DLC3.

Turn the ignition switch on (IG).

Turn the tester on.

Clear the DTCs (RAV4_ACA30 RM000000PDK0VSX.html).

Turn the ignition switch off.

Turn the ignition switch on (IG) and turn the tester on.

Start the engine and warm it up.

Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

Enter the following menus: Powertrain / Engine and ECT / DTC.

Read DTCs.

Result
Result
Proceed to
DTC P0171 or P0172 is output
A
DTC is not output
B

END

A

16.CHECK HARNESS AND CONNECTOR

Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM (RAV4_ACA30 RM000000UZ306OX.html).
HINT:
Repair any problems.

NEXT

17.CHECK WHETHER DTC OUTPUT RECURS

Connect the intelligent tester to the DLC3.

Turn the ignition switch on (IG).

Turn the tester on.

Clear the DTCs (RAV4_ACA30 RM000000PDK0VSX.html).

Turn the ignition switch off.

Turn the ignition switch on (IG) and turn the tester on.

Start the engine and warm it up.

Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

Enter the following menus: Powertrain / Engine and ECT / DTC.

Read DTCs.

Result
Result
Proceed to
DTC P0171 or P0172 is output
A
DTC is not output
B

END

A

18.CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER - ECM)

Disconnect the mass air flow meter connector.

Disconnect the ECM connector.

Measure the resistance according to the value(s) in the table below.
Standard Resistance (Check for Open):
Tester Connection
Condition
Specified Condition
B1-5 (VG) - B32-118 (VG)
Always
Below 1 Ω
B1-4 (E2G) - B32-116 (E2G)
Always
Below 1 Ω
Standard Resistance (Check for Short):
Tester Connection
Condition
Specified Condition
B1-5 (VG) or B32-118 (VG) - Body ground
Always
10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

19.REPLACE MASS AIR FLOW METER ASSEMBLY

Replace the mass air flow meter assembly (RAV4_ACA30 RM0000017TY00UX.html).
HINT:
If the result of the inspection performed in step 6 indicated no problem, proceed to the next step without replacing the mass air flow meter assembly.

NEXT

20.CONFIRM WHETHER MALFUNCTION HAS BEEN SUCCESSFULLY REPAIRED

Connect the intelligent tester to the DLC3.

Turn the ignition switch on (IG).

Turn the tester on.

Clear the DTCs (RAV4_ACA30 RM000000PDK0VSX.html).

Turn the ignition switch off.

Turn the ignition switch on (IG) and turn the tester on.

Start the engine and warm it up.

Drive the vehicle in accordance with the driving pattern described in Confirmation Driving Pattern.

Enter the following menus: Powertrain / Engine and ECT / DTC.

Read DTCs.

Result
Result
Proceed to
DTC is not output
A
DTC P0171 or P0172 is output
B

REPLACE ECM (RAV4_ACA30 RM0000017UO01FX.html)

END

21.CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - NO. 1 INTEGRATION RELAY)

Disconnect the air fuel ratio sensor connector.

Remove the integration relay from the engine room No. 1 relay block.

Measure the resistance according to the value(s) in the table below.
Standard resistance (Check for open):
Tester Connection
Condition
Specified Condition
B7-2 (+B) - 1A-4
Always
Below 1 Ω
Standard resistance (Check for short):
Tester Connection
Condition
Specified Condition
B7-2 (+B) or 1A-4 - Body ground
Always
10 kΩ or higher

Reconnect the air fuel ratio sensor connector.

Reinstall the integration relay.

REPAIR OR REPLACE HARNESS OR CONNECTOR

CHECK ECM POWER SOURCE CIRCUIT (RAV4_ACA30 RM000001DN807EX.html)

Result	Proceed to
DTC is not output	A
DTC P0171 or P0172 is output	B