OBD-II Trouble Code Library
A curated reference of common generic OBD-II codes. These are fault-condition indicators, not a replacement-part diagnosis.
Random or multiple cylinder misfire detected
The engine control unit has detected misfire events distributed across multiple cylinders.
Read explanation →P0301Cylinder 1 misfire detected
Misfire detected on cylinder 1; the cylinder-numbering convention depends on engine design.
Read explanation →P0302Cylinder 2 misfire detected
Misfire detected on cylinder 2; numbering varies by make and engine.
Read explanation →P0420Catalyst system efficiency below threshold (bank 1)
The monitoring system reports catalyst efficiency below its calibrated threshold on bank 1.
Read explanation →P0430Catalyst system efficiency below threshold (bank 2)
Catalyst monitor reports efficiency below its threshold on engine bank 2.
Read explanation →P0171System too lean (bank 1)
Long-term fuel correction indicates an air-fuel mixture leaner than expected on bank 1.
Read explanation →P0174System too lean (bank 2)
The fuel-control system identifies a persistently lean condition on bank 2.
Read explanation →P0101Mass or volume air flow circuit range/performance
Measured air flow falls outside the expected model of engine operating conditions.
Read explanation →P0128Coolant thermostat: temperature below regulating range
Coolant temperature does not reach the calibrated threshold in time.
Read explanation →P0442Evaporative emission system small leak detected
The EVAP system failed a small-leak integrity test.
Read explanation →P0455EVAP system gross leak detected
EVAP integrity test indicates a comparatively large leak or unsealed condition.
Read explanation →P0456EVAP system very small leak detected
EVAP monitor detected a very small vapor leak.
Read explanation →P0500Vehicle speed sensor malfunction
A fault was detected in a vehicle-speed input used by one or more control modules.
Read explanation →P0700Transmission control system malfunction request
A transmission-related control module has requested the malfunction indicator light. The code itself usually does not reveal the underlying fault.
Read explanation →P0335Crankshaft position sensor A circuit malfunction
The ECM detects a problem with the crankshaft position signal or circuit.
Read explanation →P0340Camshaft position sensor A circuit malfunction (bank 1 or single sensor)
The camshaft position signal or its circuit is not behaving as expected.
Read explanation →P0401Exhaust gas recirculation flow insufficient detected
The EGR monitor sees less exhaust gas recirculation than commanded.
Read explanation →P0562System voltage low
The control module detected supply voltage below its expected range.
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