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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 60 (Engine Controls [Self-Diagnostics 2.3L]) >> Diagnostic Tests >> DTC P0420: Catalyst System Efficiency - Below Threshold >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
  1. If FREEZE FRAME DATA has been recorded, go to next step. If FREEZE FRAME DATA has not been recorded, record FREEZE FRAME DATA. Go to next step.
  2. Verify Related Repair Information Availability -  Check for related Service Bulletins and/or on-line repair information availability. If any related repair information is available, perform repair or diagnosis according to available repair information. If vehicle is not repaired, go to next step. If related repair information is not available, go to next step.
  3. Verify Related Pending Code Or Stored DTCs -  Turn ignition off, then on (engine off). Verify related PENDING CODE or stored DTCs. If no other DTCs are present, go to next step. If any other DTC is present, go to appropriate DTC trouble shooting procedure. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  4. Inspect Gas Leakage Of Exhaust System -  Visually inspect exhaust gas leakage in exhaust system. If exhaust leakage is not present, go to next step. If any exhaust gas leakage is present, repair or replace faulty exhaust component. After repair, go to step  7.
  5. Inspect Installation Of Front & Rear HO2Ss -  Inspect for looseness of front and rear HO2Ss. If front and rear HO2Ss are tight, go to next step. If any front or rear HO2S is loose, retighten loose HO2S. After repair, go to step  7.
  6. Inspect TWC -  Clear DTC using WDS or equivalent. Cycle ignition off then back on. Inspect TWC. Refer to WARM UP THREE-WAY CATALYTIC CONVERTER under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If TWC is okay, replace suspected HO2S. After repair, go to next step. If TWC is faulty, replace TWC. After repair, go to next step.
  7. Verify Trouble Shooting Of DTC P0420 Completed -  Make sure to reconnect all disconnected connectors. Turn ignition on, engine off. Clear DTC from PCM memory using WDS or equivalent. Perform MODE 1 - PCM ADAPTIVE MEMORY PRODUCE DRIVE MODE  and MODE 3 - HO2S HEATER, HO2S & TWC REPAIR VERIFICATION DRIVE MODE  under DRIVE CYCLES. If PENDING CODE of same DTC is not present, go to next step. If PENDING CODE of same DTC is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION article. After repair, go to next step.
  8. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If any DTCs are present, go to appropriate DTC inspection. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are present, trouble shooting is complete.
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