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)

for Preparation Click here


DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim includes the short-term fuel trim and the long-term fuel trim.
The short-term fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at the stoichiometric air-fuel ratio. The signal from the heated oxygen sensor indicates whether the air-fuel ratio is RICH or LEAN compared to the stoichiometric air-fuel ratio. This variance triggers a reduction in the fuel volume if the air-fuel ratio is RICH, and an increase in the fuel volume if it is LEAN.
The short-term fuel trim varies from the central value due to individual engine differences, wear over time and changes in the operating environment. The long-term fuel trim, which controls overall fuel compensation, steadies long-term deviations of the short-term fuel trim from the central value.
If both the short-term fuel trim and the long-term fuel trim are LEAN or RICH beyond a certain value, the ECM determines this as a malfunction, illuminates the MIL and sets a DTC.

DTC No.
DTC Detection Condition
Trouble Area
P0171
P0174
When air-fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on LEAN side (2 trip detection logic)
  1. Air induction system
  2. Injector blockage
  3. MAF meter
  4. ECT sensor
  5. Fuel pressure
  6. Gas leakage in exhaust system
  7. Heated oxygen sensor (sensor 1)
  8. Heated oxygen sensor (sensor 1) heater
  9. EFI MAIN relay
  10. PCV valve and hose
  11. ECM
P0172
P0175
When air-fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on RICH side (2 trip detection logic)
  1. Injector leak or blockage
  2. MAF meter
  3. ECT sensor
  4. Ignition system
  5. Fuel pressure
  6. Gas leakage in exhaust system
  7. Heated oxygen sensor (sensor 1)
  8. Heated oxygen sensor (sensor 1) heater
  9. EFI MAIN relay
  10. ECM

HINT:
  1. When DTC P0171 or P0174 is recorded, the actual air-fuel ratio is on the LEAN side. When DTC P0172 or P0175 is recorded, 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 or P0174 may be recorded. The MIL is then illuminated.
  3. If the total of the short-term fuel trim value and long-term fuel trim value is within the malfunction threshold (and ECT is more than 75°C (167°F)), the system is functioning normally.


MONITOR DESCRIPTION

Under closed-loop fuel control, fuel injection amounts that deviate from the ECM's estimated fuel amount will cause a change in the long-term fuel trim compensation value. Long-term fuel trim value is adjusted when persistent deviations in the short-term fuel trim's value are present. Also, the smoothed fuel trim learning value is adjusted when deviations from the ECM's simulated fuel injection value are present. The smoothed fuel trim learning value is a combination of smoothed short-term fuel trim (fuel feedback compensation value) and smoothed long-term fuel trim (learning value of the air-fuel ratio). When the smoothed 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 smoothed fuel trim learning value is above 40% or below -35%. The ECM interprets this as a fault in the fuel system.

A082386E12


WIRING DIAGRAM


A105223E02


A105224E04


INSPECTION PROCEDURE

HINT:
It is possible that the malfunctioning area can be found using the Active Test Control operation. The Active Test can determine if the heated oxygen sensor or other potential trouble areas are malfunctioning or not.
The injection volume can be switched to -12.5% (decrease) or +25% (increase) by the Active Test.
The Active Test procedure enables a technician to check and graph the output voltage of the heated oxygen sensors.

  1. Procedure:
    1. Connect the intelligent tester to the DLC3.
    2. Turn the engine switch on (IG).
    3. Warm up the engine by running the engine at 2,500 rpm for approximately 90 seconds.
    4. Enter the following menus: Powertrain / Engine / Active Test / Control the Injection Volume.
    5. Perform the Active Test while the engine is idling.

Standard:
The heated oxygen sensor reacts in accordance with the increase and decrease of injection volume:
+25% → RICH output: More than 0.55 V
-12.5% → LEAN output: Less than 0.4 V

NOTICE:
The heated oxygen sensor (sensor 1) output has a few seconds of delay and the heated oxygen sensor (sensor 2) output has a maximum of 20 seconds of delay.
If the vehicle is short on fuel, the air-fuel ratio becomes LEAN and the DTCs will be recorded.


Case
Heated Oxygen Sensor (sensor 1) Voltage
Heated Oxygen Sensor (sensor 2) Voltage
Main Suspected Trouble Area
1
Injection Volume
+25%
-12.5%
A103184
Injection Volume
+25%
-12.5%
A103184
-
Heated Oxygen Sensor Voltage
0.55 V or more
Below 0.4 V
A103187
Heated Oxygen Sensor Voltage
0.5 V or more
Below 0.4 V
A103186
2
Injection Volume
+25%
-12.5%
A103184
Injection Volume
+25%
-12.5%
A103184
Heated oxygen sensor (sensor 1)
Heated oxygen sensor heater (sensor 1)
Heated Oxygen Sensor Voltage
Almost
no reaction
A103185
Heated Oxygen Sensor Voltage
0.5 V or more
Below 0.4 V
A103186
3
Injection Volume
+25%
-12.5%
A103184
Injection Volume
+25%
-12.5%
A103184
Heated oxygen sensor (sensor 2)
Heated oxygen sensor heater (sensor 2)
Heated Oxygen Sensor Voltage
0.55 V or more
Below 0.4 V
A103187
Heated Oxygen Sensor Voltage
Almost
no reaction
A103185
4
Injection volume
+25%
-12.5%
A103184
Injection Volume
+25%
-12.5%
A103184
Injector fuel pressure, Exhaust gas leak, etc.
(air-fuel ratio is extremely LEAN or RICH)
Heated Oxygen Sensor Voltage
Almost
no reaction
A103185
Heated Oxygen Sensor Voltage
Almost
no reaction
A103185

HINT:
Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when a malfunction is 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 high heated oxygen sensor (sensor 1) voltage (0.55 V or more) indicates a RICH air-fuel ratio.
A low heated oxygen sensor (sensor 1) voltage (0.4 V or less) indicates a LEAN air-fuel ratio.

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

  1. Connect the intelligent tester to the DLC3.

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

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

  1. Read the DTCs.


Result:

Display (DTC output)
Proceed to
P0171, P0172, P0174 or P0175
A
P0171, P0172, P0174 or P0175 and other DTCs
B



B
GO TO RELEVANT DTC CHART
A


2.CHECK CONNECTION OF PCV HOSE

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



NG
REPAIR OR REPLACE PCV HOSE
OK


3.CHECK AIR INDUCTION SYSTEM

  1. Check the air induction system for vacuum leaks.



NG
REPAIR OR REPLACE AIR INDUCTION SYSTEM
OK


4.PERFORM ACTIVE TEST (CONTROL)

  1. Perform the Active Test Control with the intelligent tester and check the heated oxygen sensor status.

    Standard voltage:
    Heated oxygen sensor reacts in accordance with the increase and decrease of injection volume:
    +25% → RICH output: More than 0.55 V
    -12.5% → LEAN output: Less than 0.4 V


Related DTCs
Heated Oxygen Sensor Status
Condition and Heated Oxygen Sensor Condition
Misfire
Main Suspected Trouble Area
Go to Step
B1 S1
B1 S2
B2 S1
B2 S2
N/A
L/R
L/R
L/R
L/R
Normal
None
None
N/A
P0171
P0174
L
L
L
L
Actual is LEAN at all cylinders
May occur
PCV hose, air induction system, fuel pressure, MAF or ECT
A
P0172
P0175
R
R
R
R
Actual is RICH at all cylinders
None
Fuel pressure, MAF or ECT
P0171
L
L
L/R
L/R
Actual is LEAN at bank 1
May occur
Spark plug, ignition system, injector or exhaust gas leak
B
P0174
L/R
L/R
L
L
Actual is LEAN at bank 2
P0172
R
R
L/R
L/R
Actual is RICH at bank 1
None
Spark plug, ignition system or injector
C
P0175
L/R
L/R
R
R
Actual is RICH at bank 2
P0171
L
R
L/R
L/R
Heated oxygen sensor (bank 1 sensor 1) malfunction
None
Heated oxygen sensor (bank 1 sensor 1)
D
P0174
L/R
L/R
L
R
Heated oxygen sensor (bank 2 sensor 1) malfunction
None
Heated oxygen sensor (bank 2 sensor 1)
P0172
R
L
L/R
L/R
Heated oxygen sensor (bank 1 sensor 1) malfunction
None
Heated oxygen sensor (bank 1 sensor 1)
P0175
L/R
L/R
R
L
Heated oxygen sensor (bank 2 sensor 1) malfunction
None
Heated oxygen sensor (bank 2 sensor 1)

HINT:
L: During control of the Active Test, the output voltage of the heated oxygen sensor almost always indicates 0.4 V or less (LEAN).
R: During control of the Active Test, the output voltage of the heated oxygen sensor almost always indicates 0.5 V or more (RICH).



A
Go to step 5

B
Go to step 8

C
Go to step 10

D
Go to step 11

5.READ DATA LIST (COOLANT TEMP)

  1. Connect the intelligent tester to the DLC3.

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

  1. Read the Coolant Temp value when the engine is cold and warmed-up.

    Standard:
    ECT when the engine is cold: Same as ambient temperature
    ECT when the engine is warmed up: 75 to 95°C (167 to 203°F)



NG
REPLACE ENGINE COOLANT TEMPERATURE SENSOR
OK


6.READ DATA LIST (MAF)

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

  1. Allow the engine to idle until the ECT reaches 75°C (167°F).

  1. Read the MAF value at idle rpm and 3,000 rpm.

    Standard:
    MAF at idle rpm: 3 to 6 g/s (shift lever is in N position and A/C is OFF)
    MAF at 3,000 rpm: 11 to 23 g/s (shift lever is in N position and A/C is OFF)



NG
REPLACE MASS AIR FLOW METER
OK


7.CHECK FUEL PRESSURE

  1. Check the fuel pressure (Click here).



NG
REPAIR OR REPLACE FUEL SYSTEM
OK


8.CHECK FOR EXHAUST GAS LEAKAGE

OK:
No gas leakage.



NG
REPAIR OR REPLACE EXHAUST SYSTEM
OK


9.CHECK FOR SPARK AND IGNITION

HINT:
If the spark plugs or ignition system malfunction, engine misfire may occur. The misfire counter can be read with the intelligent tester. Enter the following menus: Powertrain / Engine / Data List / Primary / Cylinder #1 (to #8) Misfire Rate.



NG
REPAIR OR REPLACE IGNITION SYSTEM
OK


10.INSPECT FUEL INJECTOR

HINT:
If the injectors are malfunctioning, engine misfire may occur. The misfire counter can be read with the intelligent tester. Enter the following menus: Powertrain / Engine / Data List / Primary.



NG
REPLACE FUEL INJECTOR
OK


11.INSPECT HEATED OXYGEN SENSOR
A107602E03

  1. Disconnect the E23 and E44 sensor connectors.

  1. Measure the resistance of the sensor.

    Standard resistance:
    Tester Connection
    		Specified Condition
    E23-1 (HT1A) - E23-2 (+B)
    		11 to 16 Ω
    E44-1 (HT2A) - E44-2 (+B)
    		11 to 16 Ω
    E23-1 (HT1A) - E23-4 (E2)
    		10 kΩ or higher
    E44-1 (HT2A) - E44-4 (E2)
    		10 kΩ or higher



NG
REPLACE HEATED OXYGEN SENSOR
OK


12.INSPECT INTEGRATION RELAY (EFI MAIN)
A107685E03

  1. Remove the integration relay from the engine room No. 2 junction block.

  1. Measure the resistance of the EFI MAIN relay.

    Standard resistance:
    Terminal Connections
    		Specified Condition
    2A-8 - 2C-1
    		10 kΩ or higher
    2A-8 - 2C-1
    		Below 1 Ω
    (when battery voltage is applied to terminals 2A-6 and 2A-7)



NG
REPLACE INTEGRATION RELAY
OK


13.CHECK WIRE HARNESS (HEATED OXYGEN SENSOR (SENSOR 1) - ECM)
A107603E02

  1. Disconnect the E23 and E44 sensor connectors.

  1. Disconnect the E6 and E8 ECM connectors.

  1. Measure the resistance of the wire harness side connectors.

    Standard resistance:
    Tester Connection
    		Specified Condition
    E23-1 (HT1A) - E8-24 (HT1A)
    		Below 1 Ω
    E23-3 (OX1A) - E8-30 (OX1A)
    		Below 1 Ω
    E44-1 (HT2A) - E6-5 (HT2A)
    		Below 1 Ω
    E44-3 (OX2A) - E6-28 (OX2A)
    		Below 1 Ω
    E23-1 (HT1A) or E8-24 (HT1A) - Body ground
    		10 kΩ or higher
    E23-3 (OX1A) or E8-30 (OX1A) - Body ground
    		10 kΩ or higher
    E44-1 (HT2A) or E6-5 (HT2A) - Body ground
    		10 kΩ or higher
    E44-3 (OX2A) or E6-28 (OX2A) - Body ground
    		10 kΩ or higher



NG
REPAIR OR REPLACE HARNESS AND CONNECTOR
OK


14.REPLACE HEATED OXYGEN SENSOR

NEXT


15.PERFORM CONFIRMATION DRIVING PATTERN

A106748E01

(a) Connect the intelligent tester to the DLC3.
(b) Switch from normal mode to check mode.
(c) Warm up the engine until the ECT reaches 75°C (167°F).
(d) Drive the vehicle at 50 km/h (31 mph) or more for 3 to 5 minutes.
(e) Allow the engine to idle for 2 minutes.
(f) Perform steps "d" and "e" at least 3 times.
If a malfunction exists, the MIL is illuminated during step "f".

NOTICE:
If the conditions in this test are not strictly followed, detection of a malfunction will not occur. If you do not have the intelligent tester, turn the engine switch off after performing steps "c" to "f", and then perform steps "c" to "f" again.

(g) Confirm that no DTC is output.

NEXT

END