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Home › Lexus › 1997 › GS 300 › Repair and Diagnosis › Engine Performance › System › Engine Controls - Tests W/Codes › Circuit Tests › DTC P0420 - Catalyst System Efficiency Below Threshold › Diagnosis & Repair

Diagnosis & Repair

  1. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Start and run engine until normal operating temperature is reached. Ensure all accessories are off. Drive vehicle for 5-10 minutes at 31-40 MPH. Check for codes. If only DTC P0420 is displayed, go to next step. If other codes are displayed, diagnose and repair those codes first and retest.
  2. Check heated oxygen sensor 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 no problems are indicated, go to next step.
  3. Check bank No. 1, sensor No. 2 resistance. See SYSTEM/COMPONENT TESTS article. Replace oxygen sensor as necessary. If oxygen sensor is okay, replace catalytic converter and retest.
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