Code No. P0171: Abnormal Fuel System (lean)






OPERATION



  • Refer to Code No. P0201: No. 1 Injector System .
  • Refer to Code No. P0202: No. 2 Injector System .
  • Refer to Code No. P0203: No. 3 Injector System .
  • Refer to Code No. P0204: No. 4 Injector System .

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 10 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.
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 10 g/sec.
Judgement Criterion
  • Long-term fuel trim is more than +12.5 % for 5 seconds.


  • Short-term fuel trim is more than +12.1 % for 5 seconds.
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 10 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.
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 less than 10 g/sec.
Judgement Criterion
  • Long-term fuel trim is more than +12.5 % for 5 seconds.


  • Short-term fuel trim is more than +22.3 % for 5 seconds.
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. Check for exhaust leaks

Q. Is the check result normal?
Go to Step 2 .
Repair.

STEP 2. Check for intake system vacuum leaks.

Q. Is the check result normal?
Go to Step 3 .
Repair.

STEP 3. M.U.T.-III data list

  • Refer to Data List Reference Table .

  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?
Go to Step 4 .
Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value (Refer to Inspection Chart for Diagnosis Code ).

STEP 4. Connector Check: Injector connectors

  1. B-101 (No. 1 injector connector).
  2. B-102 (No. 2 injector connector).
  3. B-103 (No. 3 injector connector).
  4. B-104 (No. 4 injector connector).

Q. Are the check results normal?
Go to Step 5 .
Repair or replace the connector.

STEP 5. Check injector itself.

  • Check injector itself (Refer to ).

Q. Is the check result normal?
Go to Step 6 .
Replace the injector.

STEP 6. Connector check: B-08 engine-ECU connector

Q. Is the check result normal?
Go to Step 7 .
Repair or replace the connector.

STEP 7. Check harness between injector connector and engine-ECU connector.

  1. Check and repair harness between B-101 (terminal No. 2) No. 1 injector connector and B-08 (terminal No. 2) engine-ECU connector.
  2. Check and repair harness between B-102 (terminal No. 2) No. 2 injector connector and B-08 (terminal No. 3) engine-ECU connector.
  3. Check and repair harness between B-103 (terminal No. 2) No. 3 injector connector and B-08 (terminal No. 18) engine-ECU connector.
  4. Check and repair harness between B-104 (terminal No. 2) No. 4 injector connector and B-08 (terminal No. 19) engine-ECU connector.

  • Check output line for damage.

Q. Are the check result normal?
Go to Step 8 .
Repair the damaged harness wire.

STEP 8. Fuel pressure measurement.

  • Fuel pressure measurement (Refer to ).

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

STEP 9. Check fuel.

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

Q. Is the check result normal?
Go to Step 10 .
Replace the fuel.

STEP 10. 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.