14/10/2026
🔧 Top 20 Most Common OBD2 Codes — Quick Guide
OBD2 trouble codes help technicians identify problems detected by a vehicle’s engine and transmission control systems. However, an OBD2 code does not automatically mean the named component is defective. It tells you which system or circuit needs further diagnosis.
For example, P0300 indicates random or multiple-cylinder misfires. Possible causes include worn spark plugs, ignition coils, fuel-delivery problems, vacuum leaks, low compression, or injector issues. P0171/P0174 indicate a lean condition, which can be caused by vacuum leaks, incorrect MAF readings, low fuel pressure, or exhaust leaks.
Codes such as P0101 relate to MAF sensor range/performance, while P0120 indicates a throttle-position sensor circuit problem. P0340 can point toward a camshaft-position sensor circuit issue. Transmission-related codes such as P0700 indicate that the transmission control system has requested the Check Engine Light.
Other common codes include P0420 for catalyst efficiency, P0455 for a large EVAP leak, P0401 for insufficient EGR flow, and P0562 for low system voltage.
🔍 Important: Always check the wiring, connectors, power supply, grounds, vacuum lines, and related components before replacing parts. Clear the code only after repairing the root cause, then perform a road test to confirm the repair.
