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Home >> Lexus >> 2000 >> ES 300 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0420: Catalyst System Efficiency Below Threshold >> Diagnosis & Repair

Diagnosis & Repair

  1. If other DTCs are displayed, diagnose and repair those DTCs first and retest system. If only DTC P0420 is displayed, go to next step.
  2. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step.
  3. Disconnect suspect A/F sensor harness connector. One A/F sensor is located in each exhaust manifold. Measure resistance between terminal B+ (Black wire) and HT (Black/White wire on bank No. 1 or Black/Red wire on bank No. 2) at A/F sensor connector (component side). Measure resistance at both A/F sensors. Resistance should be .8-1.4 ohms at 68°F (20°C) or 1.8-3.2 ohms at 1472°F (800°C). If resistance is not as specified, replace appropriate A/F sensor. If resistance is as specified, go to next step.
  4. Check heated oxygen sensor No. 2 circuits. See DTC P0136: HEATED OXYGEN SENSOR CIRCUIT . If problem exists, repair as necessary. If problem does not exist, replace catalytic converter.
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