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Check engine codes

OBD2 P Code Lookup

Look up common check engine codes. Start with the code, then use the AI diagnostic to add symptoms, mileage, vehicle details, and driving conditions before you book a repair.

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Most Searched Codes

P0300Stop driving if it runs poorly
Random/Multiple Cylinder MisfireP0300 is a generic OBD2 powertrain code for random or multiple cylinder misfire. Unlike P0301 through P0308, it does not point to one specific cylinder, so the cause can be ignition, fuel, air, sensor, or mechanical.
P0301Stop driving if it runs poorly
Cylinder 1 MisfireP0301 means the engine computer detected repeated misfires on cylinder 1. Because it names one cylinder, diagnosis usually starts by comparing cylinder 1 ignition, fuel, and compression against the other cylinders.
P0302Stop driving if it runs poorly
Cylinder 2 MisfireP0302 is a cylinder-specific misfire code. The computer sees cylinder 2 slowing down compared with the rest of the engine.
P0303Stop driving if it runs poorly
Cylinder 3 MisfireP0303 identifies a misfire on cylinder 3. Diagnosis should prove whether the fault follows the coil, plug, injector, or stays with the cylinder.
P0304Stop driving if it runs poorly
Cylinder 4 MisfireP0304 means the powertrain computer detected a misfire on cylinder 4. It is a symptom code, not proof that one specific part failed.
P0171Diagnose soon
System Too Lean Bank 1P0171 means the engine computer is adding more fuel than normal on bank 1 because it sees too much air or not enough fuel.
P0174Diagnose soon
System Too Lean Bank 2P0174 is the bank 2 version of a lean-condition code. On V-style engines, bank 2 is the side opposite bank 1.
P0420Diagnose soon
Catalyst Efficiency Bank 1P0420 means the downstream oxygen sensor pattern suggests the bank 1 catalytic converter is not storing oxygen properly.
P0430Diagnose soon
Catalyst Efficiency Bank 2P0430 is the bank 2 catalyst-efficiency code. It usually appears on V6 or V8 engines with separate bank 1 and bank 2 converters.
P0442Usually not urgent
EVAP Small LeakP0442 means the EVAP system could not hold pressure or vacuum during a leak test, but the leak is small.
P0455Usually not urgent
EVAP Large LeakP0455 means the EVAP system failed a leak check badly enough that the computer sees a large leak or no pressure/vacuum change.
P0456Usually not urgent
EVAP Very Small LeakP0456 is a very small EVAP leak code. The leak may be too small to see without smoke testing.
P0128Diagnose soon
Coolant ThermostatP0128 means the engine warmed up slower than expected or stayed cooler than the computer expected.
P0101Diagnose soon
MAF Range/PerformanceP0101 means the mass air flow reading is outside the expected range for engine speed and load.
P0135Diagnose soon
O2 Sensor Heater Bank 1 Sensor 1P0135 points to the heater circuit for the bank 1 sensor 1 oxygen sensor. The heater helps the sensor reach operating temperature quickly.
P0141Diagnose soon
O2 Sensor Heater Bank 1 Sensor 2P0141 points to the heater circuit for the downstream oxygen sensor after the catalytic converter on bank 1.
P0507Diagnose soon
Idle RPM Higher Than ExpectedP0507 means the engine is idling above the target RPM even though the computer is trying to control idle speed.

All Codes by System

Every code links to its full page — meaning, urgency, symptoms, likely causes, and what to check first. Usually not urgent Diagnose soon Stop driving if it runs poorly

P — Powertrain Codes704 codes

Engine, transmission, fuel and emissions — the codes that turn on the check engine light.

P00xx · Fuel & Air Metering, Auxiliary Emissions56

P01xx · Fuel & Air Metering45

P02xx · Injector Circuit23

P03xx · Ignition System & Misfires45

P04xx · Auxiliary Emission Controls33

P05xx · Vehicle Speed & Idle Control56

P06xx · Computer & Output Circuits37

P07xx · Transmission92

P08xx · Transmission50

P09xx · Transmission100

P0Axx · Hybrid Propulsion16

P20xx · Fuel & Air Metering, Emissions44

P21xx · Fuel & Air Metering, Emissions23

P22xx · Fuel & Air Metering, Emissions19

P24xx · Turbo, EGR & Diesel Aftertreatment31

P34xx · Cylinder Deactivation & Valvetrain34