P0171
DTC P0171 SYSTEM TOO LEAN (BANK 1)GENERAL DESCRIPTION
In order to provide the best possible combination to 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%.
DTC DESCRIPTION
If long-term and short-term values are out of threshold value, the PCM determines that a fault exists and a DTC is stored.
DTC Detecting Condition:
MONITOR SCANTOOL DATA
1. Ignition "OFF
2. Connect Scantool and Engine "ON"
3. Monitor HO2S parameter and parameters related to Fuel System Too Lean on CURRENT DATA.
4. Are the parameters related to Fuel System Too Lean displayed within specifications?
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, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.
NO: Check Sensors and Injectors related to this Fuel System Too Lean according to the troubleshoting Guide. Repair or replace as necessary and Go to "System Inspection" procedure.
SYSTEM INSPECTION
1. Check Air Leakage
1. Visually/physically inspect the air leakage in intake/exhaust system as following items.
A. If OK, go to "Check for air leakage in EVAP Purge control valve" as below.
B. If NG, repair as necessary and go to "Verification of Vehicle Repair" procedure.
- 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. Check for air leakage in EVAP Purge control valve.
A. With engine idling disconnect hose from EVAP purge valve side of hose.
B. Check no vacuum at EVAP purge solenoid valve.
C. Is vacuum available at purge valve when EVAP. purge valve is not in operating?
YES: Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.
NO: Go to "Check for air leakage in Positive Crankcase Ventilation Valve(PCV)" as below.
3. Check for air leakage in Positive Crankcase Ventilation Valve(PCV).
A. Remove PCV valve from cylinder head cover by pulling ventilation hose.
B. With engine idling block PCV valve opening.
C. Confirm that vacuum is felt.
D. Remove PCV valve.
E. Blow through valve from port "A" and verify that air comes out of port "B"
F. Blow through valve from port "B" and verify that no air comes out of port "A"
G. Has a problem been found?
YES: Repair or replace as necessary and go to "Verification Vehicle Repair" procedure.
NO: Go to "Check Fuel Pressure" as below.
2. Fuel Pressure Test
NOTE:
1. 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
2. The fuel system remains under pressure when the engine is not running. Release fuel system pressure before disconnecting any fuel line to reduce the chance of personal injury or fire damage to vehicle components.
1. Check the fuel for excessive water, alcohol, or other contaminants. Replace contaminated fuel as necessary.
2. Install the fuel pressure gauge to the fuel pressure gauge adaptor.
3. Apply battery voltage to the terminal for the pump drive and activate the fuel pump: then, with fuel pressure applied, check that there is no fuel leakage from the pressure gauge or connection part.
4. Disconnect the vacuum hose from the pressure regulator, and plug the hose end. Measure the fuel pressure at idle.
Specification: 320 - 340 kPa(3.26 - 3.47 kg/sq.cm, 46 - 49 psi)
5. Measure the fuel presure when the vacuum hose is connected to the pressure regulator.
Specification: Approx. 255 kPa (2.57 kg/sq.cm, 37 psi)
6. Are the measured fuel pressure within specifications?
YES: Go to "Check injector leakage" as below.
NO: Repair or replace according to the below table. And then, go to "Verification of Vehicle Repair" procedure.
3. Check Injector Leakage
1. Ignition "OFF" after checking the Fuel Pressure Test.
2. Stop the engine and check for a change in the fuel pressure gauge reading for 5 minutes.
3. Does fuel pressure drop after engine is stopped?
YES: Go to "Component Inspection" procedure.
NO: Repair or replace according to the below table. And then, 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 troubleshooting procedure.
NO: System is performing to specification at this time.