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Mazda OBD2 Fault Codes Directory

Common diagnostic trouble codes for Mazda vehicles including Mazda 3, Mazda 6, CX-5, CX-9, CX-30, Miata MX-5. Select a code below to view model-specific symptoms, causes, and DIY fix tutorials.

Mazda P0420 Moderate

Catalyst System Efficiency Below Threshold (Bank 1)

Diagnose Mazda P0420 error. Learn symptoms, safe driving radius, and recommended replacement parts.

Exhaust & Emissions System Repair Steps β†’
Mazda P0171 Moderate to High

System Too Lean (Bank 1)

Diagnose Mazda P0171 error. Learn symptoms, safe driving radius, and recommended replacement parts.

Fuel & Air Metering System Repair Steps β†’
Mazda P0300 Critical (Flashing CEL = Stop Immediately)

Random or Multiple Cylinder Misfire Detected

Diagnose Mazda P0300 error. Learn symptoms, safe driving radius, and recommended replacement parts.

Ignition & Combustion System Repair Steps β†’
Mazda P0128 Moderate

Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Diagnose Mazda P0128 error. Learn symptoms, safe driving radius, and recommended replacement parts.

Engine Cooling System Repair Steps β†’
Mazda P0455 Minor to Moderate

Evaporative Emission System Leak Detected (Gross Leak / Large Leak)

Diagnose Mazda P0455 error. Learn symptoms, safe driving radius, and recommended replacement parts.

EVAP Emissions System Repair Steps β†’
Mazda P0135 Moderate

O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

Diagnose Mazda P0135 error. Learn symptoms, safe driving radius, and recommended replacement parts.

Exhaust & Emissions (Upstream O2) Repair Steps β†’
Mazda P0507 Minor to Moderate

Idle Air Control System RPM Higher Than Expected

Diagnose Mazda P0507 error. Learn symptoms, safe driving radius, and recommended replacement parts.

Air Intake & Throttle Control Repair Steps β†’