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Home › Mazda › 2002 › MPV ES › Repair and Diagnosis › Engine Performance › System › Engine Controls - Self-Diagnostics › Diagnostic Tests › DTC P0421 Or DTC P0431 › Diagnostic Procedures

Diagnostic Procedures

  1. Record freeze frame data. Check for service bulletins and on-line information. Repair as necessary. After repair, go to next step.
  2. Verify Related Pending Code Or Stored DTCs -  Turn ignition on, engine off. Check for other related DTCs. If no other DTCs are present, go to next step. If any other DTCs are present, diagnose and repair those first. Refer to DIAGNOSTIC TROUBLE CODE IDENTIFICATION .
  3. Inspect Gas Leakage Of Exhaust System -  Inspect exhaust system for any leakage. If exhaust system is okay, go to next step. If leaks are present, repair or replace exhaust components as necessary. After repair, go to step  7.
  4. Inspect Installation Of Front And Rear Heated Oxygen Sensors -  Inspect front and rear HO2Ss. If both HO2Ss are tight, go to next step. If either HO2S is loose, tighten as necessary. After repair, go to step  7.
  5. Inspect Front HO2S Voltage -  Using scan tool, access PID O2S11 for P0421 or PID O2S21 for P0431. Monitor PID while racing engine (in park or neutral). If PID reading is more than 0.45 volt when accelerator is suddenly depressed (rich condition) or less than 0.45 volt just after releasing accelerator pedal (lean condition), replace WU-TWC converter. After repair, go to next step. If PID reading is not as specified, replace suspected HO2S. After repair, go to next step.
  6. Verify Trouble Shooting Of DTC P0421 Or P0431 Completed -  Reconnect all components. Turn ignition on, engine off. Using scan tool, clear DTC. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine and perform MODE 1 - PCM ADAPTIVE MEMORY PRODUCE DRIVE MODE  and MODE 3 - HO2S HEATER, HO2S & TWC REPAIR VERIFICATION DRIVE MODE  under DRIVE MODES. Using scan tool, recheck DTCs. If DTC P0421 or P0431 is present, replace PCM. After repair, go to next step. If DTC P0421 or P0431 is not present, go to next step.
  7. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If no other DTCs are present, testing is complete. If any other DTC is present, go to applicable test and repair.
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