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Emission Controls Trouble Codes: List & Fixes

P04xx codes cover auxiliary emission controls: exhaust gas recirculation (EGR), secondary air injection, catalytic converter efficiency and the evaporative emission (EVAP) system. They seldom affect how the car drives, but they will usually fail a smog check or emissions test. For small EVAP leak codes, start with the simplest check – a loose, damaged or wrong gas cap – before a smoke test of the system.

97Codes
2.2Average severity
2%High or critical
20%DIY-friendly
Severity distributionSeverity distribution

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P0420 Powertrain The bank 1 catalytic converter no longer stores enough oxygen to clean the exhaust properly. Low P0430 Powertrain The bank 2 converter on a V6, V8 or split-exhaust engine isn't cleaning the exhaust well enough. Low P0442 Powertrain The EVAP system leaks through an opening of about 0.040 inch — a cracked hose, loose joint… Minor P0446 Powertrain The canister vent valve isn't doing what the ECU commands — electrically or because the vent… Minor P0456 Powertrain The EVAP system has a tiny leak, about 0.020 inch — the hardest EVAP leak to find, and often… Minor P0457 Powertrain The EVAP leak test found the system wide open — almost always a loose, missing or worn gas cap. Minor

All codes (97)

All Severity 3+ Severity 4+
P2457 Powertrain The EGR cooler isn't cooling the recirculated exhaust enough – it's clogged, bypassed or low… Moderate P2458 Powertrain A DPF regen took too long or never finished, usually from short trips or exhaust that won't get… Moderate P2459 Powertrain The DPF is regenerating far more often than it should for the miles driven. Moderate P2463 Powertrain The DPF is loaded with more soot than the ECU allows; it needs a regen or cleaning before it… High P246C Powertrain The DPF is so restricted that the ECM has cut engine power to protect the turbo, EGR system… High P2BAC Powertrain EGR has been shut off because of a fault, so NOx is above the limit; fix the EGR code stored… Moderate P3081 Volkswagen · Powertrain The engine didn't warm up as fast as the ECU expected – most often a thermostat stuck open. Low

Subsystems

Fuel & Air Metering 193Ignition & Misfire 66Speed & Idle Control 57Transmission 57ECU & Outputs 54Module Communication 43Brakes, ABS & Chassis 36Body Systems 31Hybrid / EV 14