P0174
DTC P0171 SYSTEM TOO LEAN (BANK 1)DTC P0174 SYSTEM TOO LEAN (BANK 2)
GENERAL DESCRIPTION
In order to provide the best possible combination of driveablity, fuel economy and emission control, the PCM uses a closed loop air/fuel metering system. The PCM monitors the HO2S signal voltage and adjusts fuel delivery based it in closed loop fuel control. Changes in fuel delivery will be indicated by the long-term and the short-term fuel trim values. The ideal fuel trim value is around 0%. The PCM will add fuel when the HO2S signal is indicating a lean condition. Additional fuel is indicated by fuel trim values that are above 0%. The PCM will reduce fuel when the HO2S signal is indicating a rich condition. Reduction in fuel is indicated by fuel trim values that are below 0%. The DTC relevant to fuel trim will be set when the amount reaches excessive levels because of a lean or rich condition.
DTC DESCRIPTION
Checking air4uel ratio correction value every 0.75 sec. under detecting condition, if an value is within detecting condition for more than 0.3 sec., PCM sets P0171/P0174. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
DTC Detecting Condition:
MONITOR SCANTOOL DATA
1. IG "OFF" & connect Scantool.
2. Warm-up the engine to normal operating temperature.
3. Monitor "Sensor/actuator related to fuel system(HO2S, MAFS, MAPS, TPS, ECTS, PSCA, Injector, and so on)" items on the service data.
4. Is the service data displayed correctly?
YES: Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, ending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
NO: Go to "Terminal and Connector Inspection" procedure
TERMINAL AND CONNECTOR INSPECTION
1. Many malfunctions in the electrical system are caused by poor harness and terminals. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.
2. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.
3. Has a problem been found?
YES: Repair as necessary and go to "Verification of Vehicle Repair" procedure
NO: Go to "System Inspection" procedure.
SYSTEM INSPECTION
1. Check air leakage
1. Visually/physically inspect the air leakage in intake/exhaust system for following items
Vacuum hoses for splits, kinks and improper connections.
Throttle body gasket
Gasket between intake manifold and cylinder head
Seals between intake manifold and fuel injectors
Exhaust system between HO2S and three way catalyst for air leakage
2. Has a problem found in this procedure?
YES: Repair or replace it which has a problem, and go to "Verification of Vehicle Repair" procedure.
NO: Go to "Check the fuel line" as follows
2. Check the fuel line
1. Check the fuel line for following items
Connector connection state
Damage/ connection state for vacuum hoses connected to fuel line
Bent/ pressed/ twisted fuel line or fuel leakage
2. Has a problem found in this procedure?
YES: Repair or replace it which has a problem, and go to "Verification of Vehicle Repair" procedure.
NO: Go to "Check fuel pressure" as follows
3. Check fuel pressure
NOTE:
- Be cautious that Fuel is explosive and an empty fuel tank can still contain explosive gases. when working on fuel system make sure to supply adequate ventilation to the work area. Do not smoke, and keep sparks and open flames away.
- The fuel system remains under pressure when the engine is not running. Release fuel system pressure before disconnecting any fuel tine to reduce the chance of personal injury or fire damage to vehicle components.
1. IG "OFF" and disconnect Fuel Pump Relay in Junction Box.
2. Start-up and wait until it stops itself.
3. IG "OFF" and connect Fuel Pump Relay.
4. Install the fuel pressure gauge to the delivery pipe with the fuel pressure gauge adaptor.
5. Activate the fuel pump, and with fuel pressure applied, check that there is no fuel leakage from the pressure gauge or connection part.
6. Disconnect the vacuum hose from the pressure regulator, and plug the hose end.
7. Measure the fuel pressure at idle.
Specification : 374.6-384.4 kpa(3.82-3.92 kg/sq.cm, 54.3 - 55.8 psi)
8. Is the measured fuel pressure within specifications?
YES: Go to "Component Inspection" procedure.
NO: Repair or replace according to the below table. And then, go to "Verification of Vehicle Repair"procedure.
COMPONENT INSPECTION
1. Check PCV
1. IG "OFF" and remove PCV valve from cylinder head
2. With engine idling, block PCV valve and confirm that vacuum is felt.
3. Insert thin stick into the screwed PCV valve and verify that the plunger is moving.
4. Is the PCV valve normally moving?
YES: Go to "Check PCSV as follows.
NO: Replace it, and go to "Verification of Vehicle Repair" procedure.
2. Check PCSV
1. IG "OFF" and disconnect PCSV and vacuum hose.
2. Connect hand-vacuum gage with PCSV and supply vacuum to it.
3. Is the vacuum maintained ?
YES: Go to "Check injector" as follows.
NO: Repair or replace it, and go to "Verification of Vehicle Repair" procedure.
3. Check injector
1. IG "OFF" and disconnect injector.
2. Check it for blocking caused by any foreign substance.
Specification:
3. Measure resistance between terminals 1 and 2 of Injector connector.(Component side)
4. Is the measured resistance within specification?
YES: Go to "Check sensor/actuator related to fuel system" as follows
NO: Repair or replace it, and go to "Verification of Vehicle Repair" procedure.
4. Check sensor/actuator related to fuel system
1. Check the signal of sensor/actuator related to fuel system(HO2S, MAFS,MAPS, TPS, ECTS, PCSV, Injector and so on) (Refer to each DTC diagnostic procedure)
2. Are all of these items normal?
YES: Substitute with a known - good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
NO: Repair it, and go to "Verification of Vehicle Repair" procedure.
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verify that the fault has been corrected.
1. Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code(DTC) which has been diagnosed.
2. Using a Scantool, Clear the DTCs
3. Operate the vehicle within conditions noted in the freeze frame data or enable conditions
4. Monitor that all readiness tests have been verified as "Complete"
5. Are any DTCs present?
YES: Go to the applicable trouble shooting procedure.
NO: System is performing to specification at this time.