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Home >> Kia >> 2003 >> Spectra Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0420: Main Catalyst Efficiency Below Threshold >> Test Procedure
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Test Procedure

  1. Turn ignition off. Connect Hi-Scan Pro/Kia Data Pro Scan tool or equivalent to OBD-II Data Link Connector. See Figure . Turn ignition on. Monitor for other DTCs. If DTCs P0115, P0116, P0030-P0032, P0036-P0038, P0130-P0134, P0136-P0138, P0140 and/or P0170-P0172 are set, do all repairs associated with those DTCs before continuing with this procedure. If no other DTCs are set, go to next step.
  2. Start engine. Allow engine to idle until reaches normal operating temperature for more than 10 minutes. Using Hi-Scan Pro/Kia Data Pro Scan tool or equivalent, monitor front and rear HO2S voltage signal. If front and rear HO2S voltage signal switches from lean to rich or rich to lean, replace catalytic converter and go to step  10 . If voltage signal is not as specified, go to next step.
  3. Turn ignition off. Release fuel pressure from fuel system. Install fuel pressure gauge at fuel rail. For proper fuel pressure test. See FUEL PRESSURE (SPECTRA) under FUEL SYSTEM - DELIVERY in SYSTEM & COMPONENT TESTING article. Fuel pressure should be 46-51 psi (320-350 kPa) at idle. If fuel pressure is as specified, go to step  6 . If fuel pressure is too high: go to next step. If fuel pressure is too low: go to step  5 .
  4. Turn ignition off. Release fuel pressure from fuel system. Disconnect fuel return line hose from fuel rail and blow through line towards fuel tank. If fuel return line is restricted, repair or replace as necessary and go to step  10 . If return fuel line is okay, replace fuel pressure regulator and go to step 10 .
  5. With engine running, clamp fuel delivery line before fuel rail and check for fuel pressure to rise. If fuel pressure rises, replace fuel pump and go to step  10 . If fuel pressure does not rises, check on-line fuel filter and fuel pump pick-up screen for restriction. If filters are okay replace fuel pump and go to step  10 . If fuel filters are faulty, repair or replace as necessary, and go to step  10 .
  6. With engine running. Check exhaust system for leaks, cracks or loose connection (specially at exhaust manifold, catalytic converter around rear HO2S etc.). If exhaust leak is not found, go to next step. If exhaust leak is found, repair exhaust leak as necessary and go to step  10 .
  7. Check Positive Crankcase Ventilation (PCV) valve operation. Also check vacuum hoses for splits and proper connections to engine (especially at PCV system, Idle Air Control (IAC) valve, throttle body, intake manifold and brake booster). If PCV valve operation, vacuum hoses and hose connections are okay, go to next step. If PCV valve and vacuum hoses are found split, damaged or disconnected, repair or replace as necessary and go to step  10 .
  8. Check fuel injectors for proper operation and volume test. See appropriate FUEL INJECTOR TEST under FUEL SYSTEM - CONTROL in SYSTEM & COMPONENT TESTING article. If fuel injectors are okay, go to next step. If fuel injectors are faulty, repair or replace as necessary and go to step  10 .
  9. Visually and physically inspect the following items:
    • Throttle body gasket.
    • Gasket between intake manifold and surge tank.
    • Seals between intake manifold and fuel injectors.
    • Seals between surge tank PCV valve.

    If the above items are okay, replace catalytic converter and go to next step. If above items are faulty, repair or replace as necessary and go to next step.

  10. After repair, return vehicle to original condition. Clear codes using Hi-Scan Pro/Kia Data Pro Scan tool or equivalent. Verify repairs by driving vehicle and monitoring for pending codes. If DTC is set during test drive, follow appropriate DTC test procedure.
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