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Home >> Toyota >> 1998 >> Tercel Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes >> Self-Diagnostic Tests >> DTC P0420: Catalyst System Efficiency Below Threshold >> Diagnosis & Repair
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Diagnosis & Repair

  1. Connect scan tool. See Figure. Start and warm engine to normal operating temperature. Drive vehicle at 31-40 MPH for 5-10 minutes. Stop vehicle. Retrieve codes. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.
  2. If codes other than P0420 are present, diagnose and repair those codes first. If only DTC P0420 is displayed, check sensor No. 1 circuits. See DTC P0130 : HEATED OXYGEN SENSOR FAULT (SENSOR NO. 1) test. Repair wiring as necessary. If oxygen circuits are okay, go to next step.
  3. Check sensor No. 2 circuits. See DTC P0136 : HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 2) test. Repair wiring as necessary. If oxygen circuits are okay, replace catalytic converter.
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