Diagnostic Trouble Code (DTC) P0171 P0172 1AZ-FE

DTC P0171 System Too Lean (Bank 1)

DTC P0172 System Too Rich (Bank 1)

1. Description

2. Monitor description

3. Wiring diagram

4. Inspection procedure

Description. DTC P0171 P0172

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.

Toyota fault codes list

DTC No.	DTC Detection Condition	Trouble Area
P0171	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 (sensor 1) circuit A/F sensor (sensor 1) A/F sensor heater (sensor 1) Integration relay (EFI MAIN relay) A/F sensor heater and EFI MAIN relay circuits Ventilation valve and hose Ventilation hose connections ECM
P0172	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 (sensor 1) circuit A/F sensor (sensor 1) A/F sensor heater (sensor 1) Integration relay (EFI MAIN relay) A/F sensor heater and EFI MAIN relay circuits ECM

HINT:

1. When DTC P0171 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 is set, the actual air-fuel ratio is on the rich side.
2. If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 may be set. The MIL is then illuminated.
3. When the total of the short-term and long-term fuel trim values is within 20% (and the engine coolant temperature is more than 75°C [167°F]), the system is functioning normally.

Monitor description. DTC P0171 P0172

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's 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 sets a DTC. Example: The average fuel trim learning value is +38% or more or -32% or less, the ECM interprets this as a fuel system malfunction.

Wiring diagram. DTC P0171 P0172

Refer to DTC P2195.

Inspection procedure. DTC P0171 P0172

HINT:

1. 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.
2. 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.
3. A high A/F sensor voltage could be caused by a lean air-fuel mixture. Check for conditions that would cause the engine to run lean.

1. Connect the intelligent tester to the DLC3.

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

3. Select the following menu items: Powertrain / Engine and ECT / DTC.

4. Read DTCs.

Result:

Display (DTC Output)	Proceed to
P0171 or P0172	A
P0171 or P0172 and other DTCs	B

HINT:

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

B	GO TO DTC CHART

A

1. Connect the intelligent tester to the DLC3.

2. Start the engine and turn the tester ON.

3. Warm up the engine at an engine speed of 2,500 rpm for approximately 90 seconds.

4. On the tester, select the following menu items: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

5. 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).

6. Monitor the output voltages of A/F and HO2 sensors (AFS B1 S1 and O2S B1 S2) displayed on the tester.

Result:

The A/F sensor reacts in accordance with increases and decreases in the fuel injection volume:

+25% = Rich output:

Less than 3.0 V

-12.5% = Lean output:

More than 3.35 V

NOTICE:

The A/F sensor has an output delay of a few seconds and the 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%		-
	Output Voltage More than 3.35 V Less than 3.0 V		Output Voltage More than 0.5 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
	Output Voltage Almost no reaction		Output Voltage More than 0.5 V Less than 0.4 V
3	Injection volume +25% -12.5%		Injection Volume +25% -12.5%		Extremely rich or lean actual air-fuel ratio Injector leakage or blockage Gas leakage from exhaust system Fuel pressure MAF meter ECT sensor Air induction system Ventilation hose connections
	Output Voltage Almost no reaction		Output Voltage Almost no reaction

1. Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the A/F and HO2 sensors.
2. To display the graph, select the following menu items on the tester: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / Enter / View / AFS B1 S1 and O2S B1 S2.

Result:

Result	Proceed to
Case 1	C
Case 2	B
Case 3	A

B	Перейдите к шагу 11
C	Перейдите к шагу 15

A

1. Connect the intelligent tester to the DLC3.

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

3. Select the following menu items: Powertrain / Engine and ECT / Data List / Primary / MAF and Coolant Temp.

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

5. 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 0.54 g/sec. and 4.33 g/sec. (M/T), Between 0.58 g/sec. and 4.67 g/sec. (A/T), (shift position: N, A/C: OFF). MAF at engine speed of 2,500 rpm: Between 3.33 g/sec. and 9.17 g/sec. (shift position: N, A/C: OFF).

NG	REPLACE MASS AIR FLOW METER

OK

1. Connect the intelligent tester to the DLC3.

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

3. Select the following menu items: Powertrain / Engine and ECT / 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°C and 100°C (167°F and 212°F).

NG	REPLACE ENGINE COOLANT TEMPERATURE SENSOR

OK

1. Check for Ventilation hose connections.

   OK:

   Ventilation hose is connected correctly and is not damaged.

NG	REPAIR OR REPLACE VENTILATION HOSE

OK

1. Check the air induction system for vacuum leakage.

   OK:

   No leakage from air induction system.

NG	REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK

1. Remove the ignition coil from the cylinder head.

2. Install the spark plug onto the ignition coil.

3. Connect the intelligent tester to the DLC3.

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

5. Select the following menu items: Powertrain / Engine and ECT / Active Test / Control the All Cylinder Fuel Cut.

6. Attach the spark plug assembly to the cylinder head.

7. Perform the Control the All Cylinder Fuel Cut operation (press the RIGHT or LEFT button to change the ON).

   NOTICE:

   When Control the All Cylinder Fuel Cut is OFF and the engine is cranked, fuel injection will occur.

8. Crank the engine for the less than 2 seconds and check the spark.

   OK:

   Sparks jump across electrode gap.

9. Install the ignition coil.

NG	REPAIR OR REPLACE IGNITION SYSTEM

OK

1. Check for exhaust gas leakage.

   OK:

   No gas leakage.

NG	REPAIR OR REPLACE EXHAUST SYSTEM

OK

1. Check the fuel pressure.

   Standard pressure:

   304 to 343 kPa (3.1 to 3.5 kgf/cm², 44.1 to 49.7 psi)

NG	REPAIR OR REPLACE FUEL SYSTEM

OK

1. Check the injection volume.

   Standard injection volume:

   76 to 92 cm³(4.6 to 5.6 cu in.) per 15 seconds

NG	REPLACE FUEL INJECTOR ASSEMBLY

OK

1. Disconnect the B7 A/F sensor connector.

2. Measure the resistance of the A/F sensor connector.

   Standard resistance:

   Tester Connection	Specified Condition
   HA1A (1) - +B (2)	1.8 ? to 3.4 ? at 20°C (68°F)
   HA1A (1) - A1A- (4)	10 k? or higher

3. Reconnect the A/F sensor connector.

NG	REPLACE AIR FUEL RATIO SENSOR

OK

1. Remove the integration relay from the engine room relay block.

2. Inspect the EFI MAIN fuse.

   

   1. Remove the EFI MAIN fuse from the integration relay.

   2. Measure the EFI MAIN fuse resistance.

      Standard resistance:

      Below 1 ?

   3. Reinstall the EFI MAIN fuse.

3. Inspect the EFI MAIN relay.

   1. Measure the EFI MAIN relay resistance.

      Standard resistance:

      Tester Connection	Specified Condition
      1C-1 - 1A-4	10 k? or higher
      	Below 1 ? (Apply battery voltage between terminals 1A-2 and 1A-3)

4. Reinstall the integration relay.

NG	REPLACE INTEGRATION RELAY

OK

1. Disconnect the B7 A/F sensor connector.

2. Turn the ignition switch on (IG).

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

   Standard voltage:

   Tester Connection	Specified Condition
   +B (B7-2) - Body ground	9 to 14 V

4. Turn the ignition switch off.

5. Disconnect the B32 ECM connector.

6. Measure the resistance.

   Standard resistance (Check for open):

   Tester Connections	Specified Conditions
   HA1A (B7-1) - HA1A (B32-109)	Below 1 ?
   A1A+ (B7-3) - A1A+ (B32-112)	Below 1 ?
   A1A- (B7-4) - A1A- (B32-113)	Below 1 ?

   Standard resistance (Check for short):

   Tester Connections	Specified Conditions
   HA1A (B7-1) or HA1A (B32-109) - Body ground	10 k? or higher
   A1A+ (B7-3) or A1A+ (B32-112) - Body ground	10 k? or higher
   A1A- (B7-4) or A1A- (B32-113) - Body ground	10 k? or higher

7. Reconnect the ECM connector.

8. Reconnect the A/F sensor connector.

   

NG	REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

NEXT

1. (a) Connect the intelligent tester to the DLC3.
2. (b) Turn the ignition switch on (IG) and turn the tester ON.
3. (c) Clear DTCs.
4. (d) Switch the ECM from normal mode to check mode using the tester.
5. (e) Start the engine and warm it up with all the accessories switched OFF.
6. (f) Drive the vehicle at between 38 mph and 75 mph (60 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).

   NOTICE:

   If the conditions in this test are not strictly followed, no malfunction will be detected.

NEXT

1. On the intelligent tester, select the following menu items: Powertrain / Engine and ECT / DTC.

2. Read DTCs.

Result:

Display (DTC Output)	Proceed to
No output	A
P0171 or P0172	B

B	Перейдите к шагу 3

A
END