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HOMESERVICE MANUALSPONTIAC2003VIBE BASE, FWD, STANDARDREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - SELF-DIAGNOSTICSDIAGNOSTIC TESTSDTC P0420: CATALYST SYSTEM LOW EFFICIENCYDIAGNOSTIC AIDS
2003 Pontiac Vibe Base, FWD, Standard

Diagnostic Aids

2003 Pontiac Vibe Base, FWD, StandardSECTION Diagnostic Aids

Check for any of the following conditions:

  • A contaminated or malfunctioning HO2S can cause inaccurate sensor readings. For checks of HO2S, see DIAGNOSTIC AIDS  in DTC P0130.
  • Observe HO2S 1 voltage and fuel trim readings with a scan tool. If HO2S 1 voltage is fixed low, while fuel trim is constantly high, check Mass Air Flow (MAF) sensor signal circuit for resistance. High circuit resistance can cause sensor to read a lower volume of air than actual, resulting in a lean fueling condition. This lean fueling condition can cause HO2S 2 voltage to be fixed low, causing DTC P0420 diagnostic to fail.
  • A damaged HO2S wiring harness. Check HO2S wiring harnesses for damage and repair as necessary.
  • If a DTC P0420 is intermittent, driving vehicle under conditions outlined in Inspection/Maintenance (I/M) section can verify whether fault is present. See INSPECTION/MAINTENANCE CATALYST SYSTEM SET PROCEDURE  under INSPECTION/MAINTENANCE PROCEDURES.
  • After returning to an idle, the HO2S 1 signal may stay rich or lean for several seconds, causing the test to be delayed.

A catalytic converter failure may be caused by any of the following conditions:

  • An engine misfire.
  • An inadequate secondary ignition voltage.
  • Any excessive engine oil or engine coolant consumption.
  • A rich engine fueling.
An intermittent malfunction may be caused by faults in HO2S electrical circuits. Check wiring harness and components for an intermittent condition. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 1.8L VIBE article. The information included in freeze frame data can be useful in determining vehicle operating conditions when DTC first set.

RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.