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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 61 (Engine Controls [Self-Diagnostics 3.0L]) >> Diagnostic Tests >> DTC P0421 Or DTC P0431 >> 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 pending code or stored DTCs using WDS or equivalent. If any other DTC is present, go to appropriate DTC trouble shooting procedure. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are present, go to next step.
  4. Inspect Gas Leakage From Exhaust System -  Visually check if any exhaust gas leakage is found in exhaust system. If no exhaust gas leakage is present, go to next step. If any exhaust leak is present, repair or replace faulty exhaust part. After repair, go to step  7.
  5. Inspect Installation Of HO2Ss -  Check if HO2S (RF, LF, RR, LR) are loosely installed. If HO2S installation is okay, go to next step. If any HO2Ss are loose, retighten suspected HO2S. After repair, go to step  7.
  6. Inspect WU-TWCs -  Clear DTC from PCM memory using WDS or equivalent. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Cycle ignition off, then back on. Inspect WU-TWCs for each bank. Refer to WARM UP THREE-WAY CATALYTIC CONVERTER under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If WU-TWCs are okay, go to next step. If any WU-TWC is faulty, replace faulty WU-TWC. After repair, go to next step.
  7. Verify Trouble Shooting Of DTC P0421 Or P0431 Is Completed -  Make sure to reconnect all disconnected connectors. Turn ignition on, engine off. Clear DTC from memory using WDS or equivalent. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine and perform MODE 1 - PCM ADAPTIVE MEMORY PRODUCE DRIVE MODE , MODE 2 - EGR SYSTEM REPAIR VERIFICATION DRIVE MODE  and MODE 3 - HO2S HEATER, HO2S & TWC REPAIR VERIFICATION DRIVE MODE  . 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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