OBD-II FAQ
Common questions about OBD-II codes, diagnostics, and vehicle trouble codes.
What is OBD-II?
OBD-II is the standardized vehicle diagnostic system required in all US cars since 1996 that monitors emissions and engine performance.
What is the difference between OBD-I and OBD-II?
OBD-I (1981-1995) used manufacturer-specific systems, while OBD-II (1996+) standardized connectors, codes, and protocols across all brands.
What does the Check Engine Light mean?
The Check Engine Light means the OBD-II system detected an engine, transmission, or emissions problem. A flashing light means stop driving immediately.
What cars have OBD-II?
All US cars since 1996, all European gasoline cars since 2001, and diesel cars since 2003 have OBD-II.
How do I read OBD-II codes?
Plug a scan tool into the 16-pin OBD-II port under your dash, or visit an auto parts store for free code reading.
How are OBD-II codes formatted?
OBD-II codes use 5 characters: a letter (P/B/C/U for system type), then 4 digits identifying the specific fault.
Can I drive with the Check Engine Light on?
A steady light usually means you can drive briefly but get it checked soon. A flashing light means pull over and seek immediate service.
How do I clear the Check Engine Light?
Use a scan tool to clear codes, or disconnect the battery briefly. But always fix the problem first, or the light will return.
What are the OBD-II communication protocols?
Five protocols: J1850 PWM (Ford), J1850 VPW (GM), ISO 9141, ISO 14230 (KWP2000), and CAN (mandatory since 2008).