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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 Hi-Scan Pro/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 purge solenoid valve for proper installation and operation. If problem exists, repair as necessary. If problem does not exist, go to next step.
  2. Start engine and let idle, disconnect hose between EVAP valve and canister, with valve not operating check for vacuum at EVAP valve. If vacuum is present repair according to DTC P0443. See DTC P0443: EVAP SYSTEM PURGE CONTROL CIRCUIT MALFUNCTION  .
  3. 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.
  4. 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.
  5. Start engine and bring to operating temperature. Backprobe and monitor voltage between front HO2S connector terminal No. 4 (Red/Black 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.
  6. 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.
  7. Turn ignition off. Check Mass Airflow (MAF) sensor for contamination, deterioration or damage. If problem exists, clean or replace MAF sensor as necessary. If problem does not exist, go to next step.
  8. Disconnect TP sensor 3-pin connector. Measure resistance between TP sensor connector terminals No. 1 and 3 (White/Green 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.
  9. Start and idle engine. Backprobe and measure MAF signal voltage between ECM connector terminal No. 36 (Green/Blue wire) and ground. See Figure . At idle voltage should be .6-.8 volts. Open throttle slowly and verify voltage increases with air flow. See MAF SENSOR OUTPUT SPECIFICATIONS  table. If voltages are within specifications, go to next step. If voltages are not within specifications, check MAF sensor connector, ECM connector and wiring (Green/Blue wire) between MAF sensor and ECM. See Figure . If problem exists, repair connector or wiring as necessary. If problem does not exist, replace MAF sensor with a good known unit. If problem is corrected, replace MAF sensor.
  10. Turn ignition off. Disconnect TP sensor 3-pin connector and ECM connector B04. Measure resistance of White/Green wire between TP sensor connector terminal No. 1 and ECM connector B04 terminal No. 7. See Figure and Figure . Also measure resistance of Blue/Green wire between TP sensor connector terminal No. 2 and ECM connector B03 terminal No. 15. And measure resistance of Blue/Orange wire between TP sensor connector terminal No. 3 and ECM connector B04 terminal No. 17. If each resistance is less than one ohm, go to next step. If any resistance is one ohm or more, check for open circuit in appropriate wire between TP sensor and ECM. Repair wiring as necessary.
  11. Disconnect MAF sensor 3-pin connector. Measure resistance of Yellow wire between MAF sensor connector terminal No. 1 and ECM connector B03 terminal No. 23. See Figure and Figure . Also, measure resistance of Green/Blue wire between MAF sensor connector terminal No. 2 and ECM connector B03 terminal No. 36. And measure resistance of Red/Yellow wire between MAF sensor connector terminal No. 3 and connector X03 of engine compartment fuse/relay box. See Figure . If each resistance is less than one ohm, check MAF sensor connector and ECM connector for loose, damaged or corroded terminals. If problem exists, repair appropriate connector. If any resistance is one ohm or more, repair open in appropriate wire between MAF sensor and ECM.
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