Code No. P0171: Abnormal Fuel System (lean)

OPERATION

Check code No. P0261: No. 1 injector circuit low input (Refer to ).
Check code No. P0264: No. 2 injector circuit low input (Refer to ).
Check code No. P0267: No. 3 injector circuit low 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 JUDGEMENT

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 79°C.

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 79°C.

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 79°C.

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 79°C.

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 79°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 engine coolant temperature sensor
Failed manifold absolute pressure sensor
Air intake from intake hose and intake manifold
Air intake around brake booster (such as failed check valve)
Exhaust gas leakage from exhaust manifold
Failed purge control solenoid valve
Harness damage in injector circuit, or connector damage
Failed injector
Failed fuel supply system (such as failed fuel pressure)
Entry of foreign material to fuel (such as water, diesel fuel, water removers and additive)
Harness damage in oxygen sensor circuit, or connector damage
Failed oxygen sensor (front)
Failed installation of oxygen sensor (front)
Failed engine-ECU

DIAGNOSIS PROCEDURE

*: Preparation to carry out troubleshooting

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

Q. Is any other diagnosis code than P0171 stored?

	Inspection Chart for Diagnosis Code

	Go to Step 2.

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

Refer to Data List Reference Table .

Item No. 5: Intake air temperature sensor
Item No. 6: Engine coolant temperature sensor
Item No. 8: Manifold absolute pressure sensor

Q. Are the check results normal?

	Go to Step 3.

	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 3. Check air intake from intake hose and intake manifold.

Q. Is the check result normal?

	Go to Step 4.

	Repair.

STEP 4. Check for emission leakage from exhaust manifold.

Q. Is the check result normal?

	Go to Step 5.

	Repair.

STEP 5. Check installation status of oxygen sensor (front).

Q. Is the check result normal?

	Go to Step 6.

	Repair.

STEP 6. Check of damage in O2FL, OFLE line between oxygen sensor (front) connector and engine-ECU connector

Q. Is the check result normal?

	Go to Step 7.

	Repair the connector(s) or wiring harness.

STEP 7. Check brake booster check valve.

Check valve operation check (Refer to GROUP 35A - Basic Brake System - On-Vehicle Service ).

Q. Is the check result normal?

	Go to Step 8.

	Replace the check valve.

STEP 8. Check purge control solenoid valve itself.

Check purge control solenoid valve itself (Refer to GROUP 17 - Emission Control System - Evaporative Emission Control System - Purge Control Solenoid Valve Check ).

Q. Is the check result normal?

	Go to Step 9.

	Replace the purge control solenoid valve.

STEP 9. Measure fuel pressure.

Measure fuel pressure (Refer to Fuel Pressure Test ).

Q. Is the check result normal?

	Go to Step 10.

	Repair the fuel pressure.

STEP 10. Check of damage in INJ1, INJ2, INJ3 line between injector connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 11.

	Repair the connector(s) or wiring harness.

STEP 11. Check of damage in power supply line between engine control relay connector and injector connector.

Q. Is the check result normal?

	Go to Step 12.

	Repair the connector(s) or wiring harness.

STEP 12. Check injector itself.

Check injector itself (Refer to ).

Q. Is the check result normal?

	Go to Step 13.

	Replace the injector.

STEP 13. Check fuel.

Check whether foreign materials enter into fuel such as water, diesel fuel, water removers and additives.

Q. Is the check result normal?

	Go to Step 14.

	Replace the fuel.

STEP 14. M.U.T.-III data list

Refer to Data List Reference Table .

Item No. AC: Oxygen sensor (front)

Q. Is the check result normal?

	Go to Step 15.

	Replace the oxygen sensor.

STEP 15. After checking stored freeze frame data, check diagnosis codes again.

If diagnosis code P0171 is stored while the vehicle is idling, let the vehicle idle for more than 20 minutes.
If diagnosis code P0171 is stored while the vehicle is running, let the vehicle run with the same conditions of the freeze frame data, such as the vehicle speed, the crank angle sensor and the coolant temperature sensor, for more than 10 minutes.

Q. Is diagnosis code P0171 stored?

	After replacing the oxygen sensor (front), go to Step 16.

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).

STEP 16. After checking stored freeze frame data, check diagnosis codes again.

If diagnosis code P0171 is stored while the vehicle is idling, let the vehicle idle for more than 20 minutes.
If diagnosis code P0171 is stored while the vehicle is running, let the vehicle run with the same conditions of the freeze frame data, such as the vehicle speed, the crank angle sensor and the coolant temperature sensor, for more than 10 minutes.

Q. Is diagnosis code P0171 stored?

	Replace the engine-ECU.

	Check end.