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Home >> Toyota >> 1997 >> Avalon XLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes >> Circuit 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 .
  2. If codes other than P0420 are present, diagnose and repair those codes first. If only DTC P0420 is displayed, check bank No. 1, sensor No. 1 and bank No. 2, sensor No. 1 circuits. See DTC P0130:  HEATED OXYGEN SENSOR FAULT (BANK NO. 1, SENSOR NO. 1), DTC P0150: HEATED OXYGEN SENSOR FAULT (BANK NO. 2, SENSOR NO. 1) circuit test. Repair as necessary. If oxygen circuits are okay, go to next step.
  3. Check bank No. 1, sensor No. 2 circuits. See DTC P0136:  HEATED OXYGEN SENSOR CIRCUIT (BANK NO. 1, SENSOR NO. 2) circuit test. Repair as necessary. If oxygen circuits are okay, replace catalytic converter and retest.
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