Code No. P0171: Abnormal Fuel System (lean)


OPERATION



  • Check code No. P0261: No. 1 injector circuit low input (Refer to ).
  • Check code No. P0262: No. 1 injector circuit high input (Refer to ).
  • Check code No. P0264: No. 2 injector circuit low input (Refer to ).
  • Check code No. P0265: No. 2 injector circuit high input (Refer to ).
  • Check code No. P0267: No. 3 injector circuit low input (Refer to ).
  • Check code No. P0268: No. 3 injector circuit high input (Refer to ).
  • Check code No. P0270: No. 4 injector circuit low input (Refer to ).
  • Check code No. P0271: No. 4 injector circuit high input (Refer to ).

FUNCTION



  • If the fuel system goes out of order, the fuel correction value will become larger.
  • The engine-ECU checks whether the fuel trim value is within a specified range.

TROUBLE JUDGMENT


Check Conditions
  • Engine coolant temperature is less than 100°C when the engine is started.
  • Intake air temperature is less than 60°C when the engine is started.
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is more than 76°C.
  • Air flow sensor output is more than 6.4 g/sec.
Judgement Criterion
  • Long-term fuel trim is more than +12.5 % for 5 seconds.


  • Short-term fuel trim is more than +7.0 % for 5 seconds. <4B11>
  • Short-term fuel trim is more than +10.0 % for 5 seconds. <4B12>
Check Conditions
  • Engine coolant temperature is more than 100°C when the engine is started.
  • Intake air temperature is more than 60°C when the engine is started.
  • Under the closed loop air/fuel ratio control.
  • Engine coolant temperature is more than 76°C.
  • Air flow sensor output is more than 6.4 g/sec.
Judgement Criterion
  • Long-term fuel trim is more than +12.5 % for 5 seconds.


  • Short-term fuel trim is more than +17.2 % for 5 seconds. <4B11>
  • Short-term fuel trim is more than +19.9 % for 5 seconds. <4B12>
Check Conditions
  • Engine coolant temperature is more than 76°C.
  • Under the closed loop air/fuel ratio control.
Judgement Criterion
  • Long-term fuel trim is +12.5 % for 2 seconds.


  • Short-term fuel trim is +25.0 % for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION



  • None

PROBABLE CAUSES



  • Failed intake air temperature sensor
  • Failed air flow sensor
  • Failed injector
  • Air drawn in from gaps in gasket, seals, etc.
  • Failed engine coolant temperature sensor
  • Failed manifold absolute pressure sensor
  • Failed barometric pressure sensor
  • Exhaust leak
  • Incorrect fuel pressure
  • Use of incorrect or contaminated fuel
  • Harness damage in injector circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III diagnosis code

Q. Is any other diagnosis code than P0171 set?
Inspection chart for diagnosis code (Refer to ).
Go to Step 2.

STEP 2. M.U.T.-III data list

  • Data list reference table (Refer to ).

  1. Item 5: Intake air temperature sensor
  2. Item 6: Engine coolant temperature sensor
  3. Item 8: Manifold absolute pressure sensor
  4. Item 10: Air flow sensor
  5. Item BB: Barometric pressure sensor

Q. Are the check results normal?
YES : Go to Step 3.
Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value. Inspection chart for diagnosis code (Refer to ).

STEP 3. Check for exhaust leaks

Q. Is the check result normal?
Go to Step 4.
Repair.

STEP 4. Check for intake system vacuum leaks.

Q. Is the check result normal?
Go to Step 5.
Repair.

STEP 5. Check injector itself.

  • No. 1 injector connector.
  • No. 2 injector connector.
  • No. 3 injector connector.
  • No. 4 injector connector.
  • Injector check (Refer to ).

Q. Is the check result normal?
Go to Step 6.
Repair or replace the connector or replace the injector.

STEP 6. Check harness between injector connector and engine-ECU connector.

  1. Check and repair harness between No. 1 injector connector terminal and engine-ECU connector terminal INJ1.
  2. Check and repair harness between No. 2 injector connector terminal and engine-ECU connector terminal INJ2.
  3. Check and repair harness between No. 3 injector connector terminal and engine-ECU connector terminal INJ3.
  4. Check and repair harness between No. 4 injector connector terminal and engine-ECU connector terminal INJ4.

  • Check output line for damage.

Q. Are the check results normal?
Go to Step 7.
Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Fuel pressure measurement.

  • Fuel pressure test (Refer to ).

Q. Is the check result normal?
Go to Step 8.
Repair.

STEP 8. Check fuel.

  • Check for entry of foreign matter (water, diesel fuel, etc.) into fuel.

Q. Is the check result normal?
Go to Step 9.
Replace the fuel.

STEP 9. Replace the injector.

  • After replacing the injector, reconfirm whether the diagnosis code is set.

Q. Is the diagnosis code set?
Replace the engine-ECU.
Check end.