DTC    P0171    System Too Lean (Bank 1)

DTC    P0172    System Too Rich (Bank 1)

for Preparation Click here


DESCRIPTION

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 trim.
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 warm engine and stable air fuel ratio feedback, fuel trim considerably in error to lean side
(2 trip detection logic)
  1. Intake system
  2. Fuel injector assembly
  3. Mass air flow meter
  4. Manifold absolute pressure sensor
  5. Engine coolant temperature sensor
  6. Fuel pressure
  7. Gas leaks from exhaust system
  8. Open or short in air fuel ratio sensor (bank 1 sensor 1) circuit
  9. Air fuel ratio sensor (bank 1 sensor 1)
  10. Air fuel ratio sensor heater (bank 1 sensor 1)
  11. Air fuel ratio sensor heater (bank 1 sensor 1) circuit
  12. PCV valve and hose
  13. PCV hose connections
  14. EGR valve assembly
  15. ECM
P0172
With warm engine and stable air fuel ratio feedback, fuel trim considerably in error to rich side
(2 trip detection logic)
  1. Fuel injector assembly
  2. Mass air flow meter
  3. Manifold absolute pressure sensor
  4. Engine coolant temperature sensor
  5. Ignition system
  6. Fuel pressure
  7. Gas leaks from exhaust system
  8. Open or short in air fuel ratio sensor (bank 1 sensor 1) circuit
  9. Air fuel ratio sensor (bank 1 sensor 1)
  10. Air fuel ratio sensor heater (bank 1 sensor 1)
  11. Air fuel ratio sensor heater (bank 1 sensor 1) circuit
  12. EGR valve assembly
  13. 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 the malfunction threshold (and the engine coolant temperature is more than 75°C [167°F]), the system is functioning normally.


MONITOR DESCRIPTION

Under closed-loop fuel control, a fuel injection volume that deviates from that estimated by the ECM causes 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 value. Deviations from the ECM's estimated fuel injection volume also affects 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 a malfunction threshold, the ECM interprets this as a fault in the fuel system and sets a DTC.
Example:
When the average fuel trim learning value is more than +35% or less than -35%, the ECM interprets this as a fuel system malfunction.

A121607E27


CONFIRMATION DRIVING PATTERN


A199233E01

  1. Connect the intelligent tester to the DLC3.
  2. Turn the ignition switch to ON.
  3. Turn the tester on.
  4. Clear the DTCs (Click here).
  5. Turn the ignition switch off and wait for at least 30 seconds.
  6. Turn the ignition switch to ON and turn the tester on. [A]
  7. Start the engine and warm it up (until the engine coolant temperature 75°C (167°F) or higher) with all the accessories switched off. [B]
  8. With the engine warmed up, idle the engine for 2 minutes or more. [C]
  9. Drive the vehicle at between 60 and 120 km/h (38 and 75 mph) and at an engine speed of between 1400 and 3200 rpm for 5 minutes. [D]

    CAUTION:
    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

  10. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes. [E]
  11. Read the pending DTC.

    HINT:
    If a pending DTC is output, the system is malfunctioning.


WIRING DIAGRAM

Refer to DTC P0136 (Click here).
Refer to DTC P0102 for the mass air flow meter circuit (Click here).

INSPECTION PROCEDURE

HINT:
Malfunctioning areas can be identified by performing the Control the Injection Volume for A/F Sensor function provided in the Active Test. The Control the Injection Volume for A/F Sensor function can help to determine whether the air fuel ratio sensor, heated oxygen sensor and other potential trouble areas are malfunctioning.
The following instructions describe how to conduct the Control the Injection Volume for A/F Sensor operation using the intelligent tester.
  1. Connect the intelligent tester to the DLC3.
  2. Start the engine.
  3. Turn the tester on.
  4. Warm up the engine at an engine speed of 2500 rpm for approximately 90 seconds.
  5. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.
  6. Perform the Active Test operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).
  7. Monitor the voltage outputs of the air fuel ratio and heated oxygen sensors (AFS Voltage B1 S1 and O2S B1 S2) displayed on the tester.

HINT:
  1. The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
  2. Each sensor reacts in accordance with increases and decreases in the fuel injection volume.


Tester Display (Sensor)
Injection Volume
Status
Voltage
AFS Voltage B1 S1
(Air fuel ratio)
+25%
Rich
Less than 3.1 V
-12.5%
Lean
More than 3.4 V
O2S B1 S2
(Heated oxygen)
+25%
Rich
 More than 0.55 V
-12.5%
Lean
Less than 0.4 V

NOTICE:
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.


Case
Air Fuel Ratio Sensor (Sensor 1) Output Voltage
Heated Oxygen Sensor (Sensor 2) Output Voltage
Main Suspected Trouble Area
1
A150787E01
A151324E04
A150787E01
A150788E01
-
2
A150787E01
A150790E01
A150787E01
A150788E01
  1. Air fuel ratio sensor
  2. Air fuel ratio sensor heater
  3. Air fuel ratio sensor circuit
3
A150787E01
A151324E04
A150787E01
A150790E01
  1. Heated oxygen sensor
  2. Heated oxygen sensor heater
  3. Heated oxygen sensor circuit
  4. Gas leakage from exhaust system
4
A150787E01
A150790E01
A150787E01
A150790E01
  1. Fuel pressure
  2. Gas leakage from exhaust system (Air fuel ratio extremely lean or rich)
  1. Following the Control the Injection Volume for A/F Sensor procedure enables technicians to check and graph the voltage outputs of both the air fuel ratio and heated oxygen sensors.
  2. To display the graph, enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / AFS Voltage B1S1 and O2S B1S2; then press the view button on the Data List screen.

NOTICE:
Inspect the fuses for circuits related to this system before performing the following inspection procedure.

HINT:
  1. Sensor 1 refers to the sensor closest to the engine assembly.
  2. Sensor 2 refers to the sensor farthest away from the engine assembly.
  3. 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 be helpful in determining whether the vehicle was moving or stationary, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
  4. 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.
  5. 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 ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0171 OR P0172)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the ignition switch to ON.

  1. Turn the tester on.

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

  1. Read the DTCs.
    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.



B
GO TO DTC CHART (Click here)
A


2.CHECK PCV HOSE CONNECTIONS

  1. Check the PCV hose connections (Click here).

    OK:
    PCV hose is connected correctly and is not damaged.



NG
REPAIR OR REPLACE PCV HOSE
OK


3.CHECK INTAKE SYSTEM

  1. Check the intake system for vacuum leaks (Click here).

    OK:
    No leaks in intake system.



NG
REPAIR OR REPLACE INTAKE SYSTEM
OK


4.PERFORM ACTIVE TEST USING INTELLIGENT TESTER (AIR FUEL RATIO CONTROL)

  1. Connect the intelligent tester to the DLC3.

  1. Start the engine.

  1. Turn the tester on.

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

  1. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

  1. Perform the Control the Injection Volume for A/F Sensor operation with the engine idling (press the RIGHT or LEFT button to change the fuel injection volume).

  1. Monitor the voltage outputs of the air fuel ratio sensor and the heated oxygen sensor (AFS Voltage B1S1 and O2S B1S2) displayed on the tester.

    HINT:
    1. The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 25%.
    2. Each sensor reacts in accordance with increases and decreases in the fuel injection volume.
    3. 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.


    Standard:

    Tester Display
    (Sensor)
    		Injection Volume
    		Status
    		Voltage
    AFS Voltage B1S1
    (air fuel ratio)
    		+25%
    		Rich
    		Less than 3.1 V
    -12.5%
    		Lean
    		More than 3.4 V
    O2S B1S2
    (heated oxygen)
    		+25%
    		Rich
    		 More than 0.55 V
    -12.5%
    		Lean
    		Less than 0.4 V


    Result 
    Status
    AFS Voltage B1S1
    		Status
    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
    1. PCV valve and hose
    2. PCV hose connections
    3. Injector blockage
    4. Gas leak from exhaust system
    5. Intake system
    6. Fuel pressure
    7. Mass air flow meter
    8. Manifold absolute pressure sensor
    9. Engine coolant temperature sensor
    Rich
    		Rich
    		Actual air fuel ratio rich
    		-
    1. Injector blockage
    2. Gas leak from exhaust system
    3. Ignition system
    4. Fuel pressure
    5. Mass air flow meter
    6. Manifold absolute pressure sensor
    7. Engine coolant temperature sensor
    Lean
    		Lean/Rich
    		Air fuel ratio sensor malfunction
    		-
    1. Air fuel ratio sensor
    2. EGR valve
    		B
    Rich
    		Lean/Rich
    		Air fuel ratio sensor malfunction
    		-
    1. Air fuel ratio sensor
    Lean: During the Control the Injection Volume for A/F Sensor Active Test, the air fuel ratio sensor output voltage (AFS) is consistently more than 3.4 V, and the heated oxygen sensor output voltage (O2S) is consistently less than 0.4 V.
    Rich: During Control the Injection Volume for A/F Sensor of the Active Test, the AFS Voltage B1S1 is consistently less than 3.1 V, and the O2S B1S1 is consistently more than 0.55 V.
    Lean/Rich: During the Control the Injection Volume for A/F Sensor Active Test, the output voltage of the heated oxygen sensor alternates correctly.



B
Go to step 12
A


5.READ VALUE USING INTELLIGENT TESTER (COOLANT TEMP)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the ignition switch to ON.

  1. Turn the tester on.

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

  1. Read the Data List twice, when the engine is both cold and warmed up.

    Standard value:
    With cold engine:
    Same as ambient air temperature.
    With warm engine:
    80 to 100°C (176 to 212°F).



NG
REPLACE ENGINE COOLANT TEMPERATURE SENSOR (Click here)
OK


6.READ VALUE USING INTELLIGENT TESTER (MAP)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the ignition switch ON and turn the intelligent tester on.

  1. Enter the following menus: Powertrain / Engine and ECT / Data List / MAP.

  1. Read the MAP value.

    OK:
    Same value as the actual atmospheric pressure.

    HINT:
    1. Standard atmospheric pressure is 101 kPa (758 mmHg). For every 100 m increase in altitude, pressure drops by 1 kPa (7.50 mmHg).
      Varies by weather (high atmospheric pressure, low atmospheric pressure).
    2. Also, check "Atmospheric Pressure" in the Data List.



NG
REPLACE MANIFOLD ABSOLUTE PRESSURE SENSOR (Click here)
OK


7.READ VALUE USING INTELLIGENT TESTER (MAF)

  1. Connect the intelligent tester to the DLC3.

  1. Start the engine.

  1. Turn the tester on.

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

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

  1. Read MAF with the engine speed at 2500 rpm.

    Standard:
    Between 2.3 gm/sec and 6.0 gm/sec (shift lever: neutral; A/C: Off).



NG
Go to step 19
OK


8.CHECK FUEL PRESSURE

  1. Check the fuel pressure (Click here).



NG
REPAIR OR REPLACE FUEL SYSTEM
OK


9.CHECK FOR EXHAUST GAS LEAK

  1. Check for exhaust gas leaks from the exhaust manifold sub-assembly and exhaust pipes.

OK:
No gas leaks.



NG
REPAIR OR REPLACE EXHAUST GAS LEAKAGE POINT
OK


10.CHECK FOR SPARK AND IGNITION

  1. Check the ignition system (Click here).



NG
REPAIR OR REPLACE IGNITION SYSTEM (Click here)
OK


11.INSPECT FUEL INJECTOR ASSEMBLY (INJECTION VOLUME)

  1. Inspect the fuel injection volume (Click here).



OK
Go to step 16

NG
REPLACE FUEL INJECTOR ASSEMBLY (Click here)

12.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)


    A170689E24

  1. Disconnect the air fuel ratio sensor connector.

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

    Standard Resistance:
    Tester Connection
    		Condition
    		Specified Condition
    1 (HA1A) - 2 (+B)
    		20°C (68°F)
    		1.8 to 3.4 Ω
    1 (HA1A) - 4 (A1A-)
    		Always
    		10 kΩ or higher

    Text in Illustration 
    *a
    		Component without harness connected
    (Air Fuel Ratio Sensor)

  1. Reconnect the air fuel ratio sensor connector.



NG
REPLACE AIR FUEL RATIO SENSOR (Click here)
OK


13.CHECK TERMINAL VOLTAGE (POWER SOURCE OF AIR FUEL RATIO SENSOR)


    A079114E39

  1. Disconnect the air fuel ratio sensor connector.

  1. Turn the ignition switch to ON.

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

    Standard Voltage:
    Tester Connection
    		Switch Condition
    		Specified Condition
    B34-2 (+B) - Body ground
    		Ignition switch ON
    		11 to 14 V

    Text in Illustration 
    *a
    		Front view of wire harness connector
    (to Air Fuel Ratio Sensor)

  1. Reconnect the air fuel ratio sensor connector.



NG
Go to step 24
OK


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

  1. Disconnect the air fuel ratio sensor connector.

  1. Disconnect the ECM connector.

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

    Standard Resistance (Check for Open):
    Tester Connection
    		Condition
    		Specified Condition
    C34-1 (HA1A) - B8-104 (HA1A)
    		Always
    		Below 1 Ω
    C34-3 (A1A+) - B8-103 (A1A+)
    		Always
    		Below 1 Ω
    C34-4 (A1A-) - B8-126 (A1A-)
    		Always
    		Below 1 Ω

    Standard Resistance (Check for Short):
    Tester Connection
    		Condition
    		Specified Condition
    C34-1 (HA1A) or B8-104 (HA1A) - Body ground
    		Always
    		10 kΩ or higher
    C34-3 (A1A+) or B8-103 (A1A+) - Body ground
    		Always
    		10 kΩ or higher
    C34-4 (A1A-) or B8-126 (A1A-) - Body ground
    		Always
    		10 kΩ or higher

  1. Reconnect the air fuel ratio sensor connector.

  1. Reconnect the ECM connector.



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK


15.REPLACE AIR FUEL RATIO SENSOR

  1. Replace the air fuel ratio sensor (Click here).


NEXT


16.CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

  1. Perform the confirmation driving pattern.

    HINT:
    Refer to the CONFIRMATION DRIVING PATTERN.

Result 
Result
Proceed to
No DTCs output
(No pending DTCs output)
A
DTC P0171 or P0172
B


B
Go to step 17
A

END 

17.PERFORM ACTIVE TEST USING INTELLIGENT TESTER (CONTROL THE EGR STEP POSITION)

  1. Connect the intelligent tester to the DLC3.

  1. Turn the ignition switch to ON.

  1. Turn the tester on.

  1. Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or more.

    HINT:
    The A/C switch and all accessory switches should be off.

  1. Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position.

  1. Check the MAP and Engine Speed in Date List at the idling condition while performing Active Test.

    OK:
    MAP and idling condition change in response to EGR step position.


    Standard:

    -
    		EGR Step Position (Active Test)
    0 Steps
    		0 to 30 Steps
    Idling condition
    		Steady idling
    		Idling changes from steady to rough idling
    MAP
    (Data List)
    		MAP value is 20 to 40 kPa (150 to 300 mmHg)
    (EGR valve is fully closed)
    		MAP value is at least +10 kPa (75 mmHg) higher than when EGR valve is fully closed

    HINT:
    1. Do not leave the EGR valve open for 10 seconds or more during the Active Test.
    2. Be sure to return the EGR valve to step 0 when Active Test is completed.

    Result 
    Result
    		Proceed to
    NG
    		A
    OK
    		B



B
Go to step 19
A


18.INSPECT EGR VALVE ASSEMBLY

  1. Remove the EGR valve assembly (Click here).

  1. Check if the EGR valve is stuck open.

    OK:
    EGR valve is tightly closed (It is not stuck open).

  1. Reinstall the EGR valve assembly (Click here).



NG
REPLACE EGR VALVE ASSEMBLY (Click here)
OK


19.CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER CONNECTOR CONNECTION)

  1. Check the connection and terminal contact pressure of connectors and wire harnesses between the mass air flow meter and ECM (Click here).


NEXT


20.CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

  1. Perform the confirmation driving pattern.

    HINT:
    Refer to the CONFIRMATION DRIVING PATTERN.

Result 
Result
Proceed to
DTC P0171 or P0172
A
No DTCs output
(No pending DTCs output)
B


B
END
A


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

  1. Disconnect the mass air flow meter connector.

  1. Disconnect the ECM connector.

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

    Standard Resistance (Check for Open):
    Tester Connection
    		Condition
    		Specified Condition
    B53-5 (VG) - B8-69 (VG)
    		Always
    		Below 1 Ω
    B53-4 (E2G) - B8-92 (E2G)

    Standard Resistance (Check for Short):
    Tester Connection
    		Condition
    		Specified Condition
    B53-5 (VG) or B8-69 (VG) - Body ground
    		Always
    		10 kΩ or higher

  1. Reconnect the mass air flow meter connector.

  1. Reconnect the ECM connector.



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK


22.REPLACE MASS AIR FLOW METER

  1. Replace the mass air flow meter (Click here).

    HINT:
    If the result of the inspection performed in step 7 indicated no problem, proceed to the next step without replacing the mass air flow meter.


NEXT


23.CHECK WHETHER DTC OUTPUT RECURS (DTC P0171 OR P0172)

  1. Perform the confirmation driving pattern.

    HINT:
    Refer to the CONFIRMATION DRIVING PATTERN.

Result 
Result
Proceed to
No DTCs output
(No pending DTCs output)
A
DTC P0171 or P0172
B


B
REPLACE ECM (Click here)
A

END 

24.CHECK HARNESS AND CONNECTOR (AIR FUEL RATIO SENSOR - INTEGRATION RELAY)

  1. Disconnect the air fuel ratio sensor connector.

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

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

    Standard Resistance (Check for Open):
    Tester Connection
    		Condition
    		Specified Condition
    B34-2 (+B) - 1E-1
    		Always
    		Below 1 Ω

    Standard Resistance (Check for Short):
    Tester Connection
    		Condition
    		Specified Condition
    B34-2 (+B) or 1E-1 - Body ground
    		Always
    		10 kΩ or higher

  1. Reconnect the air fuel ratio sensor connector.

  1. Reinstall the integration relay.



NG
REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

REPAIR OR REPLACE ECM POWER SOURCE CIRCUIT (Click here)