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DTC P0171: System Too Lean: Procedure

NOTE: If any fuel injector, HO2S, Engine Coolant Temperature (ECT) sensor or Mass Airflow (MAF) sensor codes are present, repair those first. Using scan tool, clear DTCs. Drive vehicle with Kia Data Pro connected to OBD-II Data Link Connector (OBD-II DLC) and monitor for pending codes. If DTC P0171 returns, perform following procedure.
  1. Check vacuum hoses for leaks. Check PCV valve operation. Check for vacuum at EVAP canister when purge is not operating. Check purge solenoid valve for proper installation and operation. See DTC P0443: EVAP SYSTEM PURGE CONTROL CIRCUIT MALFUNCTION  . If problem exists, repair as necessary. If problem does not exist, go to next step.
  2. Perform fuel pressure test. Perform maximum fuel pressure test. Perform fuel pressure hold test. See appropriate tests under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If all tests are within specifications, go to next step. If any test is not within specifications, repair fuel system as necessary.
  3. Perform fuel injector inspection and volume test. See appropriate test under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If problem exists, clean or replace fuel injectors as necessary. If problem does not exist, go to next step.
    CAUTION: DO NOT spray carburetor cleaner on or near coils or plug wires. Allow enough time between checking areas for carburetor spray to dissipate.
  4. Start engine and bring to operating temperature. Backprobe and monitor voltage between front HO2S harness connector terminal No. 4 (Green/Brown wire) and ground. See Figure . With engine idling, spray short bursts of aerosol carburetor cleaner in following areas while observing voltage changes:
    • Throttle body gasket.
    • Gasket between intake manifold and cylinder head.
    • Gasket between intake manifold and surge tank.
    • Gasket between intake manifold and cylinder head.
    • Seals between intake manifold and fuel injectors.
    • Seal between surge tank and PCV pipe.
    A rise in voltage that lasts about as long as duration of carburetor cleaner spray indicates an intake leak. If leak is indicated, repair as necessary. If no leak is indicated, go to next step.
  5. With engine idling, have helper hold wadded rag against tailpipe. Listen for exhaust leaks between main catalytic converter and cylinder head. If exhaust leak is detected, repair as necessary. If exhaust leak is not detected, go to next step.
  6. With engine at idle, remove one injector harness connector measure decrease in engine RPM. Perform in sequence remaining injectors. Any cylinder with little or no change in RPM, inspect for faulty injector, repair as necessary.
  7. Engine off remove spark plugs (note location) inspect spark plugs for abnormality. If any spark plug with abnormal color is found, inspect engine for mechanical failure. Perform compression test, repair as necessary.
  8. Turn ignition off. Check Mass Airflow (MAF) sensor for contamination, deterioration or damage. If problem exists, clean or replace MAF sensor as necessary. For testing of MAF, see DTC P0101: MASS AIRFLOW (MAF) SENSOR RANGE/PERFORMANCE PROBLEM  . If problem does not exist, go to next step.
  9. Disconnect TP sensor 3-pin connector. Measure resistance between TP sensor harness connector terminals No. 2 and 3 (Blue/White wire and Blue/Orange wire - component side) with throttle valve closed and while smoothly opening throttle valve. See Figure . When throttle valve is closed, resistance should be 1.6-2.4 k/ohms. As throttle valve is opened, resistance should increase linearly. Replace TP sensor as necessary. If TP sensor is okay, go to next step.
  10. Start and idle engine. Backprobe and measure voltage between ECM harness connector terminal No. 41 (Red/White wire) and ground. See Figure . With engine at idle verify voltage is about .8 - 1.1 volts. If voltage is within specifications, go to next step. If voltage is not within specifications, check MAF sensor connector, ECM connector and wiring between MAF sensor and ECM. If problem exists, repair connector or wiring as necessary. If problem does not exist, replace MAF sensor.
  11. Turn ignition off. Disconnect TP sensor 3-pin connector and ECM 88-pin connector. Measure resistance of Black/Green wire between TP sensor harness connector terminal No. 1 and ECM harness connector terminal No. 71. See Figure and Figure . Also, measure resistance of Blue/White wire between TP sensor harness connector terminal No. 2 and ECM harness connector terminal No. 59. And measure resistance of Blue/Orange wire between TP sensor harness connector terminal No. 3 and ECM harness connector terminal No. 73. If each resistance is less than one ohm, go to next step. If any resistance is one ohm or more, repair open in appropriate wire between TP sensor and ECM.
  12. Disconnect MAF sensor 4-pin connector. Measure resistance of Red/Blue wire between MAF sensor harness connector terminal No. 2 and ECM harness connector terminal No. 14. See Figure and Figure . Also, measure resistance of Red/White wire between MAF sensor harness connector terminal No. 4 and ECM harness connector terminal No. 41. And measure resistance of Black/Yellow wire between MAF sensor harness connector terminal No. 1 and ground. Ground point is located behind left side of instrument panel. If each resistance is less than one ohm, check TP sensor connector, MAF sensor connector and ECM connector for loose, damaged or corroded terminals. If problem exists, repair as necessary appropriate connector. If any resistance is one ohm or more, repair open in appropriate wire between MAF sensor and ECM.
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