DTC P0421/P0431: Warm Up Catalytic Converter Efficiency Below Limit (CALIFORNIA): Testing

NOTE: Ensure freeze frame data has been recorded. Check for service bulletins and on-line information.

Check for DTCs. If any other DTCs are present, inspect and repair first. If no other DTCs are present, go to next step.
Inspect exhaust system for any leakage. If exhaust system is okay, go to next step. If leaks are present, repair as necessary. Go to step 5 .
Inspect front and rear oxygen sensors. If both sensors are tight, go to next step. If either sensor is loose, tighten as necessary. Go to step 5 .
Erase DTC. See CLEARING CODES in SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Start engine. Check converter operation. See applicable test in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE & 626 article. If converter is faulty, replace converter. If converter is okay, replace rear oxygen sensor. After repair, go to next step.
Reconnect all components. Erase DTC. See CLEARING CODES in SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Conduct Drive Mode No. 4 under DRIVE CYCLE PROCEDURE. See SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Using scan tool, check DTCs. If DTC P0420 is pending, replace PCM and go to next step. PCM is mounted to passenger floor, behind glove box. If DTC P0420 is not pending, go to next step.
Perform after repair procedure. See AFTER REPAIR PROCEDURE . If no DTC is present, testing is complete. If any DTC is present, go to appropriate test for diagnosis and repair.