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 ).

Item 5: Intake air temperature sensor
Item 6: Engine coolant temperature sensor
Item 8: Manifold absolute pressure sensor
Item 10: Air flow sensor
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.

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