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Mazda Protege 2000 ES P0421 Code: How to Pass Inspection Without a $700 Converter?

Model: Mazda Protege Fault Code: P0421 Posted: 2008-10-10 21:43

Hi everyone, I've had the Engine Check Light on for about a year. The day before my state inspection, I had someone else reset the codes. The next day, I failed the inspection due to 'system not ready' status — three sensors were flagged: Catalyst, Evaporative System, and EGR. After driving approximately 80 miles, the ECL (Engine Control Light) came back on. I recently purchased my own OBD-II scanner and reset the codes manually while keeping it connected during driving. After 32 miles, the Catalyst Monitoring sensor became active, but the Check Engine Light returned. The Evaporative System Monitoring sensor is still not ready. My vehicle is a 2000 Mazda Protege ES. I've heard that vehicles from model years 1996–2000 may be allowed to pass inspections even if two sensors are not ready. Is this true for New Jersey? Are state-specific rules different, and where can I find official guidelines? The inspection report lists eight sensors as failing. What low-cost solutions exist to fix the P042 or P0421 issue and successfully pass the inspection? I cannot afford a $700 converter. DTC Details: - Stored Code: P0421 (Warmup Catalyst Efficiency Below Normal - Bank 1) - Freeze Frame Data: - Fuel System 1 Status: Closed Loop - Fuel System 2 Status: Not Supported - Calculated LOAD Value: 38.04% - Engine Coolant Temperature: 185.00 °F - Short Term Fuel Trim - Bank 1: -3.91% - Long Term Fuel Trim - Bank 1: 8.59% - Engine RPM: 2,074.00 rpm - Vehicle Speed Sensor: 47.85 mph Any advice on fixing this issue affordably and reliably? Thanks in advance!

Related fault codes
P0421
Comments (2)
Anonymous 2008-10-11 09:52

The number of active monitors allowed during emissions inspections varies by state. However, if the Check Engine Light is illuminated, the vehicle will fail inspection regardless of how many sensors are not ready. The P0421 code indicates a failing catalyst converter — it's not just a minor issue. If the light turns on immediately after the monitor sets, this suggests the converter is worn out rather than simply malfunctioning.

Anonymous 2008-10-30 21:13

The catalytic converter is one of the most critical components for emissions control — it filters harmful exhaust gases and significantly reduces pollution. While some states may overlook minor codes during inspections, P0421 is a major issue that cannot be ignored. There are no truly affordable or reliable 'cheap' replacements available; used converters can sometimes be found at salvage yards, but their quality is unpredictable. A full replacement is recommended, and the engine must also be properly tuned to prevent further damage to the converter. Poor fuel trim values may indicate underlying engine issues that need addressing before installing a new converter.