OBD-II Trouble Code Lookup
Type the code from your scan tool or dashboard warning and get a plain-English answer: what the code means, what causes it, how serious it is, and what the repair typically costs.
Most looked-up codes
Catalyst System Efficiency Below Threshold Bank 1
P0171System Too Lean Bank 1
P0300Random/Multiple Cylinder Misfire Detected
P0430Catalyst System Efficiency Below Threshold Bank 2
P0455EVAP System Leak Detected - Large Leak
P0128Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
P0174System Too Lean Bank 2
P0442EVAP System Leak Detected (small leak)
P0446EVAP System Vent Control Circuit
P0172System Too Rich Bank 1
P0011A Camshaft Position - Timing Over-Advanced or System Performance Bank 1
P0340Camshaft Position Sensor A Circuit Bank 1 or Single Sensor
Browse the full list of 9,415 generic codes →
Browse by system
Powertrain codes (P codes)
7,387 generic codes — engine, fuel, ignition, emissions and transmission faults — the check engine light codes.
Chassis codes (C codes)
498 generic codes — ABS, traction control, steering and suspension faults.
Body codes (B codes)
300 generic codes — airbags, seat belts, climate, seats, locks and lighting faults.
Network codes (U codes)
1,230 generic codes — communication faults between the car's control modules.
What is OBD-II?
OBD-II (On-Board Diagnostics, second generation) is the self-diagnosis system built into every car and light truck sold in the United States since 1996. The engine computer and the computers for the transmission, brakes, airbags, and body systems watch their sensors and circuits continuously. When a reading stays outside the expected range, the computer stores a diagnostic trouble code (DTC) and usually turns on the check engine light or another warning lamp.
Every code has five characters. The first letter is the system: P for powertrain (engine and transmission), C for chassis (brakes, steering, suspension), B for body (airbags, seats, climate, locks), and U for the network that lets the modules talk to each other. The second character tells you whether the code is generic (0 or 2 — the same definition on every brand) or manufacturer-specific (1 or 3). The last three characters pinpoint the circuit or system that reported the fault.
A code is a starting point, not a verdict. It names the system that saw a problem, and proper testing decides which part actually failed. That is why each page here lists the common causes in order and the checks a technician runs before replacing anything.