P0174
P0174General Description
In order to provide the best possible combination of drivability, 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 the fuel trim value under detecting condition, if its average exceeds the limit over certain period, PCM sets P0174. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
DTC Detecting Condition:
Monitor DTC Status
1. Monitor DTCs related to MAFS, MAPS, ECTS, Injector or CVVT items with scantool.
2. Are DTCs present for the systems indicated above?
YES
a. Do all repairs associated with those codes before proceeding with this procedure.
NO
a. 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. Is a problem present?
YES - Repair or replace as necessary 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. Is a problem present?
YES - Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.
NO - Go to "Check fuel pressure" as follows
3. Check fuel pressure
CAUTION
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. IG "OFF" and disconnect Fuel Pump Relay in Junction Box.
2. Start the engine and wait for the engine to stall.
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. Measure the fuel pressure at idle.
Specifications : 374.6 - 384.4 kPa(3.82 - 3.92 kg/sq.cm, 54.3 - 55.8 psi)
7. Is the measured fuel pressure within specifications ?
YES - Go to "Component Inspection" procedure.
NO - Repair or replace according to the table indicated below. And then, go to "Verification of Vehicle Repair" procedure.
Component Inspection
1. Check PCV
1. IG "OFF" and remove PCV valve from rocker cover.
2. Insert a thin stick into the PCV valve from the threaded side and verify that the plunger is moving.
3. Is the PCV valve moving normally?
YES - Go to "Check injector" as follows
NO - Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.
2. Check injector for normal operation
1. Start engine.
2. Check its RPM decrease when doing the injector's actuation test.
3. Is there any cylinder with no change in RPM or only a small change in RPM ?
YES - Clear DTC and Test-drive under enable conditions above-mentioned. After the test, If this DTC is set, go to "Inspection & Repair" procedure. If not, troubleshooting is completed.
NO - Replace injector, 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. Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode
2. Press F5(INFO) 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.