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Home >> Geo >> 1996 >> Metro Base, 2D Hatchback, 1.3 9 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0420 - Three-Way Catalyst System Efficiency Low >> Diagnosis & Repair

Diagnosis & Repair

  1. Check TWC for severe discoloration caused by excessive temperatures. Inspect for dents, holes or an internal rattle, indicating damaged catalyst. Ensure TWC meets manufacturer specifications. If any problems are found, replace TWC. If no problems are found, go to next step.
  2. Inspect exhaust system for leaks or damage. Repair as necessary. If exhaust system is okay, go to next step.
  3. Inspect HO2S2 for proper installation. Ensure HO2S2 wire harness is not in contact with exhaust pipes. Repair as necessary. If HO2S2 is okay, replace TWC and go to next step.
  4. Connect scan tool to DLC. Turn ignition on. Select CLEAR INFORMATION function. Start engine and run at 2000 RPM for 2 minutes. Monitor HO2S2 on scan tool. If HO2S2 remains somewhat inactive after several minutes at 1500 RPM, go to next step. If HO2S2 remains active, check for fuel system or engine mechanical problems. See BASIC TESTING article.
  5. Select CLEAR INFORMATION function on scan tool. Road test vehicle within FREEZE FRAME conditions that set DTC P0420. If any DTCs set, see appropriate DTC test. If no DTCs set, system is okay.
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