P0171
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 drivability, fuel economy and emission control, the ECM uses a closed loop air/fuel metering system. The ECM 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 ECM 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 ECM 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
Breaking lambda adaptation and lambda controller limits for a an extended period, which initially may have been caused by failures in the fuel or intake system, will involve emission rise, and therefore shall be diagnosed by fuel system monitoring. If same error code is set in the next driving cycle, the ECM illuminates the MIL. The lambda controller deviations, including adaptive terms, are used for fuel system monitoring. The time counter is increased if lambda controller deviations exceed a specific threshold and the ECM will then set DTC P0171/P0174 or P0172/P0175 respectively depending on the direction of the deviation. P0171/P0174 is set with positive deviation and P0172/P0175 is set with negative deviation.
DTC Detecting Condition:
MONITOR DTC STATUS
NOTE: If any codes relating to injectors, HO2S, ECT(Engine Coolant Temperature)Sensor, Throttle Position sensor or Mass Air Flow Sensor are stored, do ALL REPAIRS associated with those codes be fore proceeding with this troubleshooting tree.
1. Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode.
2. Press F4(DTAL) to select DTC information from the DTCs menu.
3. Confirm that "DTC Readiness Flag" indicates "Complete". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions.
4. Read "DTC Status" parameter.
5. Is parameter displayed "History(Not Present) fault"?
NOTE:
- History (Not Present) fault: DTC occurred but has been cleared.
- Present fault: DTC is occurring at present time.
YES: Fault is intermittent caused by poor contact in the sensor's and/or ECM's connector or was repaired and ECM memory was not cleared. Thoroughly check connectors for loose or poor connections, bending, corrosion, contamination, deterioration, or damage. Repair or replace or necessary and go to "Verification of Vehicle Repair" procedure.
NO: Go to "Monitor Actuation Test" procedure.
MONITOR ACTUATION TEST
The main purpose of this test is to identify potential engine mechanical condition problems and fuel and ignition systems problems that are not common to all cylinders. For best results, perform this test while maintaining as steady an rpm reading as possible.
CAUTION: Before beginning tests; set the parking brake, place gear selector In P or N and block drive wheels for safety.
1. Warm up the engine to normal operating temperature and let it idle.
2. Using a Scan Tool and select "INJECTOR #1" parameter on the Actuation Test mode shown in the figure.
3. Monitor engine rpm and shut off the injector #1 by pressing "STRT(F1)" key.
4. Repeat procedure on all injectors and record the engine rpm.
Specification : All cylinders should show an even RPM drop.
5. Was each cylinder's rpm drop within the same value?
YES: Go to "Air Leakage Inspection" procedure.
NO: Cylinders with the least amount of RPM drop are not contributing their share of power. Go to "Fuel Injector Inspection" procedure and check the suspect cylinders.
NOTE: If the RPM loss between cylinders is quite large(200 RPM or more) and engine has high mileage, there is possible of engine wear. Perform compression test with pressure gauge to check the engine wear.
AIR LEAKAGE INSPECTION
1. Visually/physically inspect the air leakage in intake/exhaust system as following items,
If OK, go to next step.
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.
1. Remove the manifold side vacuum hose from the EVAP canister purge valve.
2. Using a hand vacuum pump apply specified vacuum(Approx. 15 in, Hg) to the manifold side of the valve.
3. Does the valve hold vacuum?
YES: Go to "Fuel System Inspection" procedure.
NO: Repair air leakage and go to "Verification of Vehicle Repair" procedure.
FUEL SYSTEM INSPECTION
1. Check the fuel for excessive water, alcohol, or other contaminants. Replace contaminated fuel as necessary.
2. Disconnect the vacuum hose from the fuel pressure regulator and inspect the hose for the presence of fuel. If any fuel is present in the vacuum hose, replace the fuel pressure regulator. Go to next step.
3. Install a fuel pressure gauge.
4. Start engine and let it idle. With the vacuum hose from the fuel pressure regulator disconnected, inspect fuel pressure.
Specification : 320-340 kPa (3.26-3.47 kg/sq.cm, 46-49 psi)
5. Is fuel pressure within the specification?
YES: Go to "Fuel Injector Inspection" procedure as below
NO: Repair as necessary refer to inspection note as below and go to "Verification of Vehicle Repair" procedure.(Inspection Note)
FUEL INJECTOR INSPECTION
1. Check the fuel injectors for clogging or any restrictions.
- Test Condition Ignition "OFF".
- Specification : No clogging and restriction.
2. Is the fuel injector OK?
YES: Visually/physically inspect the engine mechanical problem. Repair as necessary and go to "Verification of Vehicle Repair" procedure.
NO: Check injector for contamination, deterioration, or damage. Substitute with a known-good injector and check for proper operation. If the problem is corrected, replace injector and then go to "Verification of Vehicle Repair" procedure.
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verity that the fault has been corrected.
1. Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode.
2. Press F4(DTAL) and confirm that "DTC Readiness Flag" indicates "Complete". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions.
3. Read "DTC Status" parameter.
4. Is parameter displayed "History(Not Present) fault"?
YES: System performing to specification at this time. Clear the DTC
NO: Go to the applicable troubleshooting procedure.