P0171
P0171, P0174 FUEL INJECTION SYSTEM FUNCTION
DTC Logic
DTC DETECTION LOGIC
With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from air fuel ratio (A/F) sensor 1. The ECM calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.
In case the amount of the compensation value is extremely large (the actual mixture ratio is too lean), the
ECM judges the condition as the fuel injection system malfunction and illuminates the MIL (2 trip detection logic).
DTC Detection Logic:
DTC CONFIRMATION PROCEDURE
1.PRECONDITIONING
If DTC Confirmation Procedure has been previously conducted, always perform the following procedure before conducting the next test.
1. Turn ignition switch OFF and wait at least 10 seconds.
2. Turn ignition switch ON.
3. Turn ignition switch OFF and wait at least 10 seconds.
- GO TO 2.
2.PERFORM DTC CONFIRMATION PROCEDURE-I
1. Clear the mixture ratio self-learning value. Refer to Description Special Repair Requirement
2. Start engine.
Is it difficult to start engine?
YES - GO TO 3.
NO - GO TO 4.
3.RESTART ENGINE
If it is difficult to start engine, the fuel injection system has a malfunction, too.
Crank engine while depressing accelerator pedal.
Does engine start?
YES - Go to P0171.
NO - Check exhaust and intake air leak visually.
4.PERFORM DTC CONFIRMATION PROCEDURE-II
1. Keep engine idle for at least 5 minutes.
2. Check 1st trip DTC.
Is 1st trip DTC detected?
YES - Go to P0171.
NO - GO TO 5.
5.PERFORM DTC CONFIRMATION PROCEDURE-III
1. Turn ignition switch OFF and wait at least 10 seconds.
2. Turn ignition switch ON.
3. Turn ignition switch OFF and wait at least 10 seconds.
4. Start engine.
5. Maintain the following conditions for at least 10 consecutive minutes. Hold the accelerator pedal as steady as possible.
CAUTION:
Always drive vehicle at a safe speed.
6. Check 1st trip DTC.
Is 1st trip DTC detected?
YES - Go to P0171.
NO - INSPECTION END
Diagnosis Procedure
1.CHECK EXHAUST GAS LEAK
1. Start engine and run it at idle.
2. Listen for an exhaust gas leak before three way catalyst 1.
Is exhaust gas leak detected?
YES - Repair or replace malfunctioning part.
NO - GO TO 2.
2.CHECK FOR INTAKE AIR LEAK
1. Listen for an intake air leak after the mass air flow sensor.
2. Check PCV hose connection.
Is intake air leak detected?
YES - Repair or replace malfunctioning part.
NO - GO TO 3.
3.CHECK AIR FUEL RATIO (A/F) SENSOR 1 INPUT SIGNAL CIRCUIT
1. Turn ignition switch OFF.
2. Disconnect corresponding A/F sensor 1 harness connector.
3. Disconnect ECM harness connector.
4. Check the continuity between A/F sensor 1 harness connector and ECM harness connector.
5. Check the continuity between A/F sensor 1 harness connector or ECM harness connector and ground.
6. Also check harness for short to power.
Is the inspection result normal?
YES - GO TO 4.
NO - Repair open circuit, short to ground or short to power in harness or connectors.
4.CHECK FUEL PRESSURE
Check fuel pressure. Refer to Testing and Inspection.
Is the inspection result normal?
YES - GO TO 6.
NO - GO TO 5.
5. DETECT MALFUNCTIONING PART
Check fuel hoses and fuel tubes for clogging.
Is the inspection result normal?
YES - Replace "fuel filter and fuel pump assembly".
NO - Repair or replace malfunctioning part.
6.CHECK MASS AIR FLOW SENSOR
With CONSULT-III
1. Install all removed parts.
2. Check "MASS AIR FLOW" in "DATA MONITOR" mode with CONSULT-III.
For specification, refer to [1][2]Air Temperature Sensor ( Ambient / Intake ).
With GST
1. Install all removed parts.
2. Check mass air flow sensor signal in Service $01 with GST.
For specification, refer to [1][2]Air Temperature Sensor ( Ambient / Intake ).
Is the measurement value within the specification?
YES - GO TO 7.
NO - Check connectors for rusted terminals or loose connections in the mass air flow sensor circuit or grounds. Refer to P0102.
7.CHECK FUNCTION OF FUEL INJECTOR
With CONSULT-III
1. Start engine.
2. Perform "POWER BALANCE" in "ACTIVE TEST" mode with CONSULT-III.
3. Check that each circuit produces a momentary engine speed drop.
Without CONSULT-III
1. Start engine and let it idle.
2. Listen to each fuel injector operating sound.
Clicking sounds should be heard.
Is the inspection result normal?
YES - GO TO 8.
NO - Perform trouble diagnosis for FUEL INJECTOR, refer to EC-472, "Diagnosis Procedure".
8.CHECK FUEL INJECTOR
1. Turn ignition switch OFF.
2. Confirm that the engine is cooled down and there are no fire hazards near the vehicle.
3. Disconnect all fuel injector harness connectors.
4. Remove fuel tube assembly. Refer to Removal and Installation.
Keep fuel hose and all fuel injectors connected to fuel tube.
5. For DTC P0171, reconnect fuel injector harness connectors on bank 1.
For DTC P0174, reconnect fuel injector harness connectors on bank 2.
6. Disconnect all ignition coil harness connectors.
7. Prepare pans or saucers under each fuel injector.
8. Crank engine for approximately 3 seconds.
For DTC P0171, check that fuel sprays out from fuel injectors on bank 1.
For DTC P0174, check that fuel sprays out from fuel injectors on bank 2.
Fuel should be sprayed evenly for each fuel injector.
Is the inspection result normal?
YES - GO TO 9.
NO - Replace fuel injectors from which fuel does not spray out. Always replace O-ring with new ones.
9.CHECK INTERMITTENT INCIDENT
Refer to Intermittent Incident.
- INSPECTION END