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Browse codes by system

The third character of a P0 code names the subsystem it belongs to. Codes grouped here share a system, which usually means they share causes and diagnostic steps too — a useful thing to know when you have more than one code stored.

Auxiliary emission controls 1

Exhaust Gas Recirculation Flow Insufficient

Carbon-blocked EGR passages — 45% of cases

Cooling 1

Coolant Thermostat Below Regulating Temperature

Thermostat stuck open — 64% of cases

Evaporative emissions 1

Evaporative Emission System Leak Detected (Large Leak)

Fuel cap loose, cross-threaded or with a perished seal — 45% of cases

Exhaust / emissions 1

Catalyst System Efficiency Below Threshold (Bank 1)

Catalytic converter genuinely worn out — 40% of cases

Fuel and air metering 1

System Too Lean (Bank 1)

Unmetered air leak — vacuum hose, intake boot or gasket — 42% of cases

Ignition, fuel and compression 1

Random / Multiple Cylinder Misfire Detected

Worn spark plugs, coils or leads — 38% of cases